ENGINEERING AND CFD

The mitigation of aircraft noise is a major goal of the society to reduce the harmful effects on the human health and cognitive performance when exposed to a pervasive noise level. Although several events in the past have temporarily reduced the air traffic, a long-term constant growing rate if 4- 8%p.a. of passengers has been observed in the recent years. New concepts for on-demand Urban Air Mobility evolve and thus, additionally implying an extension of urban areas. Coping with this trend, the ACARE 1 defined ambitious goals of Europe’s vision for aviation for the year 2050 in the Flightpath 2050.

Reducing drag in engineering type flows is of paramount importance. Various approaches and configurations were tackled in the past, mostly, however, dealing with incompressible flow. In this project, researchers at University of Siegen were investigating a specific oscillation type control method for sub- and supersonic channel flow, a configuration where the fluid domain is restricted by cooled lower and upper walls.

The helicopters & aeroacoustics group of the Insitute of Aerdynamics and Gasdynamics at the University of Stuttgart continues to develop their well-established and validated rotorcraft simulation framework. In addition to vibration prediction, noise reduction, and maneuver flight developments, new application areas like air taxis and distributed propulsion emerge out of industrial needs and fundamental research questions.

A direct numerical simulation (DNS) of a turbulent air/ethylene jet was conducted to further understand soot oxidation at relevant combustion regimes. The DNS computational domain comprised 1.5 billion points, which integrated a detailed soot model and a chemical kinetic mechanism that involved 41 chemical species. Diverging from previous works primarily focused on soot formation, this project investigates the later stages of soot evolution, particularly its oxidation in turbulent flames. The roles of OH radicals and molecular oxygen in oxidizing soot particles, along with their distribution across mixture fraction space, were analyzed. Leveraging the dataset, an assessment of existing subfilter models for soot-gas phase interaction,…

Lattice Boltzmann method (LBM) with phase-field model has been performed to investigate the growth habit of a single ice crystal. Given the multitude of growth habits, pronounced sensitivity to ambient conditions and wide range of scales involved, snowflake crystals are particularly challenging. Only few models are able to reproduce the diversity observed regarding snowflake morphology. It is particularly difficult to perform reliable numerical simulations of snow crystals. Here, we present a modified phase-field model that describes vapor-ice phase transition through anisotropic surface tension, surface diffusion, condensation, and water molecule depletion rate.

A direct numerical simulation (DNS) with finite rate chemistry has been performed to investigate the influence of flame-wall interaction (FWI) on carbon monoxide (CO) emissions in very lean turbulent premixed methane flames. CO emissions are affected by the mean strain rate of the turbulent flow, the FWI, and the interactions of the flame with the recirculation zones of the flow. The CO production and consumption in the turbulent flame differ strongly from the reaction rates in a freely propagating flame.

Using a combination of computational simulations and experiments, researchers at the Ruhr University Bochum are investigating the complex dynamics that govern how cracks propagate in brittle and quasi-brittle materials, such as glass and hard rock. The work has implications both for mining and mineral extraction, as well as designing safer buildings.

A team of researchers led by TU Ilmenau Professor Jörg Schumacher have been using the JUWELS supercomputer at the Jülich Supercomputing Centre to run highly detailed direct numerical simulations (DNS) of turbulent flows at the so-called mesoscale—the intermediate range where both small-scale turbulent fluid interactions and large-scale fluid dynamics converge.

The Scalasca project brings together HPC experts in pursuit of new ways to measure and improve performance for increasingly large, heterogeneous architectures.

This project collates individual applications from the Fluid Dynamics group at Duisburg-Essen University. The subprojects include the investigation of phenomena from the fields of nanoparticle synthesis, supersonic flows and stratified burners using LES, DNS and direct chemistry.

A tremendous variety of physical phenomena involve turbulence, such as the dynamics of the atmosphere or the oceans, avian and airplane flight, fish and boats, sailing, heating and ventilation, and even galaxy formation. Turbulent flow is characterized by chaotic swirling movements that vary widely in size, from sub-millimeter, over the extent of storm clouds, to galactic scales. The interaction of the chaotic movements on different scales makes it challenging to simulate and understand turbulent flows. Turbulent thermal convection plays an important role in a wide range of natural and industrial settings, from astrophysical and geophysical flows to process engineering.

Turbulence has been a topic of research for many decades and finds its applications in many aspects of life. Still, turbulence is not fully understood up until today. The Navier-Stokes equations, which are used to describe the motion of viscous fluids, do not have a general analytical solution. Consequently, many researchers work with specific canonical cases to understand turbulence better. In the recent years as computers became increasingly powerful, more and more direct numerical simulations (DNS) have been conducted to solve turbulent flows. The goal of this project is to validate the scaling laws that have been derived for a turbulent round jet using Lie-symmetry analysis with numerical data.

The recent rise of renewable energy sources is promoting the use of hydrogen as a carbon-free energy carrier. One possibility to harness the energy stored in hydrogen is its usage in thermochemical energy conversion processes such as in gas turbines, industrial burners, or internal combustion engines. However, in contrast to conventional fuels, lean hydrogen/air flames are prone to thermodiffusive instabilities, which can substantially change flame dynamics, heat release rates, and flame speeds. To improve prediction capabilities of Large Eddy Simulations of hydrogen/air flames, detailed data of such flames are needed for model development and validation. However, only rare data of three-dimensional thermodiffusively unstable flames that…

As a carbon-free fuel, hydrogen has the potential of emerging as the leading energy carrier for next-generation, zero-carbon power generation, and hence has received considerable attention. Hydrogen can offer significant benefits over hydrocarbon fuels, such as wide flammability range, low ignition energy, and high diffusivity. However, the use of hydrogen in gas turbines poses considerable challenges, such as the risk of flashback due to its high flame speed, which adversely affects the performance of hydrogen combustion. Flashback, a problem that occurs in premixed combustors, is the upstream propagation of the flame from the combustor into the premixing tube due to the change in mass flow rate, which could change the combustion process…

Today, car manufacturers rely on CFD tools to design and optimise spark-ignition engines. However, current models of turbulent combustion—which are built based on the assumptions of the flamelet regime—lose their predictivity when used to simulate a highly diluted or ultra-lean combustion involving high turbulent intensities. Yet the combustion in a diluted boosted spark-ignition engine shifts from the flamelet to the thin reaction zone (TRZ) regime. This research project performed direct numerical simulations of premixed C₈H₁₈/air statistically flat flame interacting with a turbulent flow field. Results were analysed to develop a combustion model suitable for combustion in the TRZ regime based on the formalism of the coherent flame model.

Deceleration of a supersonic flow in a channel by shocks and interaction with the turbulent boundary layer leads to the formation of a complex array of shocks, subsonic and supersonic regions, and recirculation zones. In this project, high-fidelity and well-resolved large-eddy simulations (LES) of such a fully turbulent (Reδ≈105) pseudo-shock system were performed and compared with experimental data. Particular attention is paid to the occurrence of flow instabilities (such as shock motion, shock-boundary layer interaction, and symmetry breaking of the shock system), mixing behaviour in the transonic shear layer, and a comparison with sophisticated RANS turbulence models.

Micro-scale directional grooves with spanwise heterogeneity can induce large-scale vortices across the boundary layer, which is of great importance to both theoretical research and industrial applications. The direct numerical simulation approach was adopted in this project to explore flow structure and control mechanism of convergent-divergent (C-D) riblets, as well as the impact of their spacing, wavelength and height. The results show that the C-D riblets produce a well-defined secondary flow motion characterised by a pair of weak large-scale counter-rotating vortices. This roll mode can play a key role in supressing separation when the flow undergoes adverse pressure gradients, but it may also lead to the increase of friction drag.

The open-source software framework waLBerla provides a common basis for stencil codes on structured grids with special focus on computational fluid dynamics with the lattice Boltzmann method. Other codes that build upon the waLBerla core are the particle dynamics module MESA-PD and the finite element framework HYTEG. Various contributors have used waLBerla to simulate a multitude of applications, such as multiphase fluid flows, electrokinetic flows, phase-field methods and fluid-particle interaction phenomena. The software design of waLBerla is specifically aimed to exploit massively parallel computing architectures with highest efficiency.

Rotorcraft are regularly operating in ground effect over moving ship decks or on hillsides. However, only a very limited amount of research has been done to investigate the complex three-dimensional flow fields in these flight conditions and the resulting changes in rotor performance. Therefore, a hovering rotor in non-parallel ground effect was simulated in this project. URANS CFD simulations were made using various turbulence models to gain insight into the three-dimensional flow field, the rotor tip vortex evolution and the velocity distribution in the rotor plane. Best agreement with available experimental data was seen with a Reynolds stress model. Overall, the flow field was most affected close to the rotor hub and on the uphill side.

Investigations of different approaches to transition modelling on rotors were undertaken, including comparison to experimental data and results of other European CFD codes. For flows at Reynolds numbers below 500,000 the transition transport models predict unphysically large areas of laminar flow compared to the experimental data. A new boundary layer transition model was developed to improve the transition prediction for a wide range of parameters crucial to external aerodynamics. The new model was implemented into the DLR TAU code and works on either structured or unstructured grids. The agreement of the new model with the experimental data is significantly improved compared to the results of the basic transition transport model.

This project focuses on the modelling and physical understanding of 3D turbulent natural convection of non-Newtonian fluids in enclosures. This topic has wide relevance in engineering applications such as preservation of canned foods, polymer and chemical processing, bio-chemical synthesis, solar and nuclear energy, thermal energy storages. Different aspects of non-Newtonian fluids have been analysed in the course of this work: The behaviour of yield stress fluids in cubical enclosures, 2D and 3D Rayleigh-Bénard convection of power-law fluids in cylindrical and annular enclosures and finally the investigation of Prandtl number (Pr) effects near active walls on the velocity gradient and flow topologies.

In this project the flow in partially-filled pipes is investigated. This flow can be seen as a model flow for rivers and waste-water channels and represents a fundamental flow problem that is not yet fully understood. Nevertheless, there have neither been any high-resolution simulations nor well resolved experiments reported in literature to date for this flow configuration. In this project highly resolved 3D-simulations are performed which help further understanding narrow open-channel and partially-filled pipe flows. The analysis concentrates on the origin of the mean secondary flow and the role of coherent structures as well as on the time-averaged and instantaneous wall shear stress.

Researchers of Koc University, Istanbul, performed extensive large-scale direct numerical simulations of turbulent bubbly channel flows to examine combined effects of surfactant and viscoelasticity by using a fully parallelized 3D finite-difference/front-tracking method. The insights achieved shed light for the first time on the intricate interactions of soluble surfactant and viscoelasticity in complex turbulent bubbly flows and reveal their effects on friction drag in channels. The results are expected to guide practitioners in engineering designs such as heat exchangers and pipelines. 

The quality of surface water typically depends upon a complex interplay between physical, chemical and biological factors which are far from being completely understood. Most practical water quality predictions for rivers or streams rely on various simplifications esp. with regards to the turbulent flow conditions. This project aims at pushing the modeling boundary further by performing massively-parallel computer simulations which resolve all scales of hydrodynamic turbulence in river-like flows, the micro-scale flow around rigid, mobile particles, and the concentration field of suspended bacteria. The data obtained helps quantifying the shortcomings of simpler currently used prediction models and will contribute to their improvement.

While for the design point operation of centrifugal pumps an essentially steady flow field is present, the flow field gets increasingly unsteady towards off-design operation. Particular pump types as e.g. single-blade or positive displace pumps show a high unsteadiness even in the design point operation. Simulation results for the highly unsteady and turbulent flow in a centrifugal pump are presented. For statistical turbulence models an a-priori averaged turbulence spectrum is assumed, and limitations of these state-of-the-art models are discussed. Since the computational effort of a scale-resolving Large-Eddy-Simulation is tremendous, the potential of scale-adaptive turbulence models is highlighted.

Flows over the curved surface of wings, cars, turbine blades in gas turbines and impeller blades in pumps have curved streamlines. The influence of streamline curvature on flows, drag and also heat transfer in flows is substantial to large. However, engineering models have difficulties in correctly predicting flows over curved surfaces and our knowledge on streamline curvature influences on flows is still limited. In this project, turbulent flows in moderately to strongly curved channels are studied by highly accurate, large-scale numerical simulations fully resolving the turbulent fluid motions. These give important insights into streamline curvature influences on flows, and produce data that form the basis for better engineering models.

Impressive progress has recently been made in machine learning where learning capabilities at (super-)human level can now be produced in non-spiking artificial neural networks. A critical challenge for machine learning is the large number of samples required for training. This project investigated new high-throughput methods across various domains for biologically based spiking neuronal networks. Sub-projects explored tools and learning algorithms to study and enhance learning performance in biological neural networks and to equip variants of data driven models with fast learning capabilities. Applications of these learning techniques in neuromorphic hardware and design for their future application in neurorobotics were also included.

The aerodynamics of generic space launch vehicles, in particular the flow field at the bottom of the vehicle, at transonic conditions are investigated  numerically using hybrid RANS-LES methods. The focus of the project is the investigation of the impact of hot plumes and hot walls on the flow field. It is found that both higher plume velocities and higher wall temperatures shift the reattachment location downstream, leading to a stronger interaction of shear layer and plume. An additional contribution in the pressure spectral content is observed that exhibits a symmetric pressure footprint. The increased wall temperature leads to reduced radial forces on the nozzle structure due to a slower development of turbulent structures.

The need to reduce the skin-friction drag of aerodynamic vehicles is of paramount importance. Nominally 50% of the total energy consumption of an aircraft or high-speed train is due to skin-friction drag. Reducing skin-friction drag reduces fuel consumption and transport emissions, leading to vast economic savings and wider health and environmental benefits. In this project, wall-normal blowing is combined with a Bayesian Optimisation framework in order to find the optimal parameters to generate net energy savings over a turbulent boundary layer. It is found that wall-normal blowing with amplitudes of less than 1% of the freestream velocity of the boundary layer can generate a drag reduction of up to 80% with up to 5% of energy saving.

Hydrogen-enriched fuels can reduce the CO2 emissions of gas turbines. However, the presence of hydrogen in fuel mixtures can also lead to undesirable phenomena like flashback. Swirling combustors can take advantage of an axial air injection to increase their resistance against flashback. Such an example is the swirl-stabilized presented in experiments at the TU Berlin. The axial momentum ratio between the fuel jets and the air was found to control flashback resistance. This experimental hypothesis motivates the present study where large-eddy simulations of the combustion system are carried out to study the physics behind flashback phenomena in hydrogen gas turbine combustors.

Data sent over the internet relies on public key cryptographical systems to remain secure. A project under leadership of Dr. Paul Zimmermann of the French National Institute for computer science and applied mathematics (INRIA), run on HPC system JUWELS of the Jülich Supercomputing Centre, has been carrying out record computations of integer factorisation and the discrete logarithm problem, the results of which are used as a benchmark for setting the length of the keys needed to keep such systems secure.

Porous media are everywhere. When Reynolds numbers in pores are large, the unsteady inertial effects become important giving rise to the onset of turbulence, for instance in packed bed catalysis, gas turbine cooling, and pebble-bed high-temperature nuclear reactors. Access to detailed flow measurements is very challenging due to the inherent space constraints of the porous media. Therefore, a research group of the Institute of Aerospace Thermodynamics (ITLR) at University of Stuttgart uses high-fidelity direct numerical simulation (DNS) to investigate the physics of fluids inside porous media which serves for industrial 3D-printed porous media design.

Combustion remains the most important process for power generation and more research is needed to reduce future pollutant emissions. However, combustion is governed by thermo-chemical processes that interact over a wide range of length and time scales. Detailed simulations are of high interest to gain more information about flames. Two examples of large-scale simulations of challenging flame setups are given: The thermo-diffusive instabilities of hydrogen flames as well as the interplay between turbulent flow and flames. A special method for investigating the local dynamics of flames, called flame particle tracking, has been implemented specifically for large parallel clusters for high performance computing to further evaluate these cases.

Using a canonical jet in cross flow (JICF) flame configuration, researchers of TU Darmstadt performed a high-resolution DNS study concerning differential diffusion effects and mixing characteristics during hydrogen combustion. The investigations in the hydrogen JICF configurations were twofold. First, a detailed analysis of the DNS data was to yield a fundamental understanding of mixing characteristics in the JICF configuration and differential diffusion effects. Second, commonly applied tabulated chemistry approaches and their capability of predicting differential diffusion were to be validated against the DNS data. The latter, which is of highly practical interest for a related project, was the final target of this project.

The helicopters & aeroacoustics group of the Institute of Aerodynamics and Gas Dynamics at the University of Stuttgart continues to develop their well-established and validated rotorcraft simulation framework. Vibration prediction and noise reduction are currently the focus of research, and progress into manoeuvre flight situations is on the way. For two decades, high-performance computing leverged within the HELISIM project has enabled improvements for conventional helicopters as much as for the upcoming eVTOLs, commonly known as air taxis, in terms of performance, comfort, and efficiency. Community acceptance will be fostered via noise reduction and safety enhancements, made possible by this research project.

Turbulent convection is one essential process to transport heat in fluid flows. In many of the astrophysical or technological applications of convection the working fluid is characterized by a very low dimensionless Prandtl number which relates the kinematic viscosity of the fluid to its temperature diffusivity. Two important cases are turbulent convection in the Sun and turbulent heat transfer in the cooling blankets of nuclear fusion reactors. Massively parallel simulations of the simplest setting of a turbulent convection flow, Rayleigh-Bénard convection in a layer or a straight duct that is uniformly heated from below and cooled from above, help to understand the basic heat transfer mechanisms that these applications have in common.

This project explores laminar-turbulent transition, turbulence, and flow control in boundary layers at various flow speeds from the subsonic to the hypersonic regime. The physical problems under investigation deal with prediction of laminar-turbulent transition on airfoils for aircraft, prediction of critical roughness heights in laminar boundary layers, turbulent drag reduction, the origins of turbulent superstructures in turbulent flows, the use of roughness patterns for flow control, effusion cooling in laminar and turbulent supersonic boundary-layer flow, DNS of disturbance receptivity on a swept wing at high Reynolds numbers, and plasma actuator design for active control of disturbances in a swept-wing flow.

A large amount of the energy needed to push fluids through pipes worldwide is dissipated by viscous turbulence in the vicinity of solid walls. Therefore the study of wall-bounded turbulent flows is not only of theoretical interest but also of practical importance for many engineering applications. In wall-bounded turbulence the energy of the turbulent fluctuations is distributed among different scales. The largest energetic scales are denoted as superstructures or very-large-scale motions (VLSMs). In our project we carry out direct numerical simulations (DNSs) of turbulent pipe flow aiming at the understanding of the energy exchange between VLSMs and the small-scale coherent.

Large scale simulations are particularly valuable and important for a better understanding of coupled multi physics problems describing a large class of physical phenomena. This research project focuses on the development of new numerical methods for efficiently solving coupled non-linear and time-dependent fluid flow problems on a large scale. In particular, two applications are considered. Namely, the Navier–Stokes equations coupled to a transport equation describing diluted polymers and geodynamical model problems which involve non-linearities in the viscosity. The goal is to develop new methods for solving these problems, evaluating their performance and scalability, and to perform simulations based on these new methods.

Using DLR’s finite-volume solver TAU, researchers of the Institute for Aerodynamics and Flow Technology at DLR Göttingen numerically investigated the vortex system of four rotating and pitching DSA-9A blades. The computations were validated against experimental data gathered using particle image velocimetry (PIV) carried out at the rotor test facility in Göttingen. Algorithms deriving the vortex position, swirl velocity, circulation and core radius were implemented. Hover-like conditions with a fixed blade pitch were analyzed giving a good picture of the static vortex system. These results are used to understand the vortex development for the unsteady pitching conditions, which can be described as a superposition of static vortex states.

As a Lagrangian method, Smoothed Particle Hydrodynamics (SPH) has been explored and demonstrated for a wide range of applications. Several open-source frameworks exist for the large-scale parallel simulation of particle-based methods in which the resolution of simulation is fixed. Some preliminary work has also been published to tackle the difficulties encountered in extending codes with adaptive-resolution capability. However, the support for fully parallelized adaptive-resolution in distributed systems is generally still limited in the aforementioned codes. This research project focuses on an alternative approach by introducing a new multi-resolution parallel framework employing several algorithms from previous work.

The heat transfer in the stagnation region of an impinging jet at given jet to distance ratio, Re-number and Temperature ratio also depend on the turbulent inflow characteristics. Using Direct Numerical Simulations, the Nusselt-number distribution as well as the turbulent statistics close to the heated wall have been investigated. At first a calculation has been done comparing the results with published DNS and experiments from Dairay et al. (2015). Since in their paper not all necessary turbulence values were given, the missing values (e.g. turbulent length scale) had to be adjusted in order to fit their results. A good agreement has been found of our calculations with their DNS and experiments.

In order to simulate compressible multi-phase flows at extreme ambient conditions, researchers from the Institute of Aerodynamics and Gas Dynamics have developed a multi-phase flow solver based on the discontinuous Galerkin spectral element method in conjunction with an efficient tabulation technique for highly accurate equations of state. The aim of this development is the simulation of phase transition, droplet dynamics and large-scale multi-component phenomena at pressures and temperatures near the critical point. Simulations of liquid fuel injections and shock-drop interactions have been performed on the HPC systems installed at the High-Performance Computing Center Stuttgart (HLRS).

The aerodynamic flow field around helicopters is challenging to simulate due to complex configurations in relative motion. In an effort to evolve computational fluid dynamics (CFD) technology to new levels of accuracy, reliability, and parallelization efficiency, the helicopter & aeroacoustics group at the IAG of University of Stuttgart employs advanced, high-order Discontinuous Galerkin (DG) methods to help solve difficult rotorcraft-based engineering applications. Complex geometries, curved surfaces, relative motion with elaborate kinematics, and fluid-structure coupling to blade dynamics call for sophisticated techniques within the simulation tool chain to account for all important physical phenomena relevant to the field of study.

In order to quantify the uncertainty due to stochastic input in computer fluid dynamic simulations, researchers from the Institute of Aerodynamics and Gas Dynamics developed an Uncertainty Quantification framework and applied it to direct noise computations of aeroacoustic cavity flows. Simulations have been performed with the discontinuous Galerkin spectral element method on HPC system Hazel Hen at the High Performance Computing Center Stuttgart (HLRS). The aim of this investigation is to gain insight into the sensitivity of uncertain input with respect to the acoustic results and to get a reliable comparison between numerical and experimental results.

The simulation of turbulent, partially premixed flames constitutes a challenge due to the complex interplay of the mixing process of fuel and oxidizer, chemical reactions and turbulent flow. Therefore, a detailed numerical simulation of an experimentally investigated flame of laboratory scale has been performed, which allows to study these fundamental interactions in great detail. The results have been compiled into a database which aids the improvement of future combustion simulations. The simulation has been performed with an in-house solver based on OpenFOAM, which includes several performance optimizations to maximize the hardware utilization on supercomputers.

Combustion noise is an undesirable, but unavoidable by-product of turbulent combustion in, e.g., stationary gas turbines or aeronautical engines. This project combines Large Eddy Simulation (LES) of turbulent, reacting flow with advanced System Identification (SI) – a form of supervised machine learning –  to infer reduced-order models of combustion noise. Models for the source of noise on the one hand, and the flame dynamic response to acoustic perturbations on the other, are estimated to make possible the flexible and computationally efficient prediction of combustion noise across a wide variety of combustor configurations.

New wind harnessing generators that gather energy through a phenomenon known as vortex-induced vibrations could represent a new frontier for renewable energy. Researchers of the Barcelona Supercomputing Centre have been using high-performance computing system SuperMUC of the Leibniz Supercoputing Centre to help advance this technology.

Recent direct numerical simulations in closed slender Rayleigh-Bénard convection cells advanced to Rayleigh numbers of Ra = 10¹⁵ which were never obtained before and reveal a classical turbulent transport law for the heat transfer from the bottom to the top of the cell which is based on the concept of marginally stable boundary layers. Our simulations were able to resolve the complex dynamics inside the thin boundary layers at the top and bottom plates of the convection cell and to determine a steady increase of the turbulent fluctuations without an abrupt transition near the wall for a range of 8 orders of magnitude in Rayleigh number.

Recent developments in direct injection systems aim at increasing the rail pressures to more than 3000 bar for Diesel and 1000 bar for gasoline, to enhance liquid break-up and mixing which in turn improves combustion and reduces emissions. Higher flow accelerations, however, imply thermo-hydrodynamic effects, e.g. cavitation, which occurs when the pressure locally drops below saturation conditions and the liquid vaporizes. The subsequent collapse of such vapor structures causes the emission of strong shock-waves leading to material erosion. But cavitation can also be beneficial by promoting primary jet break-up, thus the ability to predict cavitation and cavitation erosion during the early stages of design of fuel injectors is desirable.

Aircraft wake vortices pose a potential threat to following aircraft. Highly resolving numerical simulations provide valuable in-sights in the physics of wake vortex behaviour during different flight phases and under various environmental conditions. Hybrid simulation techniques introduce the flowfield around detailed aircraft geometries into an atmospheric environment that controls the vortical aircraft wake until its decay. The vision of virtual flight in a realistic environment is addressed by the two-way coupling of two separate flow solvers. To mitigate the risk of wake encounters and thereby to improve runway capacity, so-called plate lines have been developed and tested at Vienna airport.

In order to analyse the complex flow in rotating turbomachinery components, researchers from the Institute for Aerodynamics and Gas Dynamics performed high fidelity, large-scale turbulent flow computations of stator-rotor interactions using the discontinuous Galerkin spectral element method on the HPC system Hazel Hen at the High Performance Computing Center Stuttgart (HLRS). The aim of this investigation is to gain insight into the intricate time-dependent behaviour of these flows and to inform future design improvements.

With constantly growing fuel prices and toughening of environmental legislation, the vehicle industry is struggling to reduce fuel consumption and decrease emission levels for the new and existing vehicles. One way to achieve this goal is to improve aerodynamic performance by decreasing aerodynamic resistance. Leveraging HPC resources, researchers of the Technical University of Munich conducted a wide range of studies with the aim to improve modeling techniques, develop a profound understanding for flow phenomena, and optimize vehicle shapes.

Recently, European legislative bodies have imposed significant restrictions on the emission level of Diesel injections systems, thus challenging car manufacturers and suppliers to reduce pollution. Improvement of the combustion process and spray quality has become a main objective in fulfilling those policies, which is mainly achieved by increasing injection pressures. Therefore, understanding internal nozzle flows has become a key aspect in designing efficient and durable Diesel injection systems. Since to this date quantitative experimental investigations are challenging, researchers use HPC technologies and computational fluid dynamics to complement experimental findings by providing additional information about the flow topology.

A series of highly resolved direct numerical simulations (DNSs) of temporally evolving turbulent non-premixed jet flames was conducted on the SuperMUC of LRZ. Two promising approaches were used to analyze the databases. The first approach, on-the-fly tracking flamelet structure, helps to understand the effects of neglecting tangential diffusion (TD) on the performance of classical flamelet models. The second approach - dissipation elements – helps to develop possible closure strategies for including flame-tangential effects in the flamelet models. Moreover, TD was used as an important performance indicator to assess tabulation strategies, differential diffusion effects, and Soret effects in turbulent non-premixed combustion.

A high fidelity, high Reynolds number direct numerical simulation (DNS) of a planar temporally evolving non-premixed jet flame was performed on the new supercomputer JUWELS of JSC. The DNS enabled the detailed investigation of combustion conditions with a high level of scale interaction between combustion chemistry and turbulence. Furthermore, the simulation was instrumental in understanding how the structure of scalar fields is affected by heat release in non-premixed flames. The insights gained from the DNS are instrumental in the development of new combustion models with the goal of improving the accuracy of simulations of real-world engineering applications.

An effective cooling of the gas turbine components subject to high thermal stresses is vital for the success of new engine and combustion concepts aiming at achieving further improvements in the energy conversion efficiency of the overall machine. The use of pulsating impinging jets - which enlarge vortex structures naturally occurring in the impinging jet flow when no pulsation is enforced - is a promising approach to develop a substantially more performant cooling system. To gain a deeper understanding of how the vortex system behaves under realistic conditions, researchers performed a DNS of a non-pulsating impinging jet flow with fully turbulent inflow conditions and compared its results with a reference case with a laminar inflow.

Researchers of the Institute of Aerodynamics at RWTH Aachen University used large-eddy simulation and computational aeroacoustics methods to analyze noise sources in turbulent flames and the interaction of the resulting acoustic waves with the flame and the turbulent flow field. To achieve accurate results of the flow and the acoustic field highly resolved large-scale simulations with several hundred million mesh points are necessary. The simulation results have given new insights into fundamental sound-generation mechanisms and their phase-relationship that are important for the prediction and control of thermoacoustic instabilities, and ultimately, the development of more efficient and gas turbines with lower pollutant emissions.

In recent years, hydroelectric power plants have received increased attention for the role they play in integrating volatile renewable energies that contribute to stabilizing the electrical grid. One major issue, though, is rooted in running turbines under conditions they were not originally designed for, leading to undesirable flow phenomena. With the standard modeling approaches that are typically used in industry simulations of hydroelectric turbines, simulation accuracy in scenarios where the turbine is used off-design is rather poor. The goal of this project is to increase simulation accuracy by the selection of suitable modeling approaches and the use of a fine mesh resolution, which is only possible by the use of supercomputers.

A GCS large-scale project under leadership of Dr.-Ing. Cifuentes of the University of Duisburg-Essen aims at understanding the physics of entrainment in turbulent premixed flames. This research characterizes the entrainment processes through the study and comparison of the flame front and the enstrophy interface. This is an essential issue in reactive turbulent flows, because a better understanding of the dynamics of the flame front and the enstrophy interface leads to better predictions of flame instabilities and scalar structures.

Shock-related buffeting is a phenomenon that occurs when air passes over the wing of an aeroplane under extreme conditions and can have profound consequences for how wings are engineered and their durability. Leveraging the computing capacities of HPC system Hazel Hen, researchers at the University of Southampton have been investigating this phenomenon using direct numerical simulations.

Spray painting is the most common application technique in coating technology. Typical atomizers used in spray coating industries are such as High-speed rotary bell and spray guns with compressed air. High-speed rotary bell atomizers provide an excellent paint film quality as well as high transfer efficiencies (approx. 90%) due to electrostatic support. Small and medium-sized enterprises continue, however, to use compressed air atomizers, although they no longer meet today's requirements from an economic and environmental point of view. It is very important to understand the atomization mechanisms of these two kinds of atomizers, in order to improve the paint quality, to reduce the overspray and to optimize the coating process.

Many wall-bounded flows in nature and technology are affected by the surface roughness of the wall. In some cases, this has adverse effects, e.g. drag increase leading to higher fuel costs; in others, it is beneficial for mixing enhancement or transfer properties. Computationally, it is notoriously difficult to simulate these flows because of the vast separation of scales in highly turbulent flows and the challenges involved in handling complex geometries. The studies are carried out in two paradigmatic and complementary systems in turbulence research, Taylor-Couette and Rayleigh-Bénard flow.

Molecular modelling and simulation is an established method for describing and predicting thermodynamic properties of fluids. This project examines interfacial properties of fluids, their contact with solid materials, interfacial fluctuations and finite-size effects, linear transport coefficients in the bulk and at interfaces and surfaces as well as transport processes near and far from equilibrium. These phenomena are investigated by massively-parallel molecular dynamics simulation based on quantitatively reliable classical-mechanical force fields.

Turbulent thermal convection plays an essential role in a wide range of natural and industrial settings, from astrophysical and geophysical flows to process engineering. While heat transfer in industrial applications takes place in confined systems, the aspect ratio in many natural instances of convection is huge. Interestingly, flow organization on enormous scales is observed in, for example, oceanic and atmospheric convection. However, our physical understanding of the formation of turbulent superstructures is limited. In this project, we analyze the flow organization within turbulent superstructures and show that their size increases when the thermal driving is increased.

The efficient mixing of fuel and oxidizer is essential in modern combustion engines. Especially in supersonic combustion the rapid mixing of fuel and oxidizer is of crucial importance as the detention time of the fuel-oxidizer mixture in the combustion chamber is only a few milliseconds. The shock-induced Richtmyer-Meshkov instability (RMI) promotes mixing and thus has the potential to increase the burning efficiency of supersonic combustion engines. To study the interaction between RMI and shock-induced reaction waves, which affects the flow field evolution und the mixing significantly, researchers leveraged HPC system SuperMUC to run 3D simulations of reacting shock-bubble interaction.

Turbulent convection flows in nature and technology often show prominent and nearly regular patterns on their largest scales which we term turbulent superstructures. Their appearance challenges the classical picture of turbulence in which a turbulent flow is considered as a tangle of chaotically moving vortices. Examples for superstructures in nature are cloud streets in the atmosphere or the granulation at the surface of the Sun. In several applications, this structure formation is additionally affected by magnetic fields. Our understanding of the origin of turbulent superstructures and their role for the turbulent transport is presently still incomplete and will be improved by direct numerical simulations of turbulent convection.

Researchers of the Institute of Aerodynamics (AIA) at RWTH Aachen University conducted large-scale benchmark simulations on supercomputer Hazel Hen of the High-Performance Computing Center Stuttgart to analyze the interaction of non-spherical particles with turbulent flows. These simulations provide a unique data base for the development of simple models which can be applied to study complex engineering problems. Such models are required in a larger research framework to improve the efficiency of pulverized coal and biomass combustion to significantly reduce the CO2 emissions.

Transient mixing and ignition play a significant role in many systems, where combustion efficiency and emissions are controlled by ignition and mixing dynamics. In the present work, high fidelity simulations of a pulsed fuel injection system are carried out using state of the art numerical tools and high-performance computing. The results contain all parameters that affect ignition dynamics and are mined and analyzed. The physics of transient reactive turbulent jets are thus identified and presented that partners in industry and academia can improve their understanding of the process and work on the design of better combustion devices.

Shock-tube experiments are a classical technique to provide data for reaction mechanisms and thus help to reduce emissions and increase the efficiency of combustion processes. A shock-tube experiment at critical conditions (low temperature), where the ignition occurs far away from the end wall, is simulated. Understanding the mechanism that leads to such a remote ignition is crucial to improve the quality of future experiments.

In order to support sustainable powertrain concepts, synthetic fuels show significant potential to be a promising solution for future mobility. It was found that the formation of soot and CO2 emissions during the energy transformation process of synthetic fuels can be reduced compared to conventional fuels and that sustainable fuel production pathways exists. Simulations of these multiphase, reactive systems are needed to fully unlock the potential of new powertrain concepts. Due to the large separation of scales, these simulations are only possible with current supercomputers.

Recently there has been a large push in the aircraft industry to reduce its carbon footprint. Laminar flow control and Natural Laminar Flow (NLF) wing design have been proposed as one of the main options for reducing the drag on the airplane and hence its fuel consumption. One of the important aspects of aircraft design concerns dynamic stability and an understanding of the unsteady behavior of NLF airfoils is important for predicting the stability characteristics of the aircraft. Recent experimental studies on NLF airfoils have shown that their dynamic behavior differs from that of turbulent airfoils and that classical linearized models for unsteady airfoils fail to predict the unsteady behavior of NLF airfoils. Most notably, NLF airfoils…

As part of the WindForS project WINSENT two wind turbines and four met masts will be installed in the Swabian Alps in Southern Germany for research proposes. The results of highly resolved numerical simulations of this wind energy test site located in complex terrain are shown. By means of Delayed Detached Eddy Simulations (DDES) the turbulent flow above a forested steep slope is analyzed in order to evaluate the inflow conditions of the planned wind turbine in detail. The complex inflow conditions and production of turbulence due to the shape of the topography and the vegetation are evaluated. The intention of using supercomputers for these applications is to analyze the local atmospheric flow field in as much detail as possible.

The accident management in a generic nuclear power plant containment with a convection flow of high-temparature gases is simulated. An activated spray mixes the turbulent flow and inhibits the formation of a possibly explosive upper region filled with hydrogen. Condensation of the steam is promoted and the maximum pressure, which may also endanger the containment integrity, is limited.

Turbulent thermal convection is ubiquitous in nature and technical applications. Inclined convection, where a fluid is confined between two differently heated parallel surfaces, which are inclined with respect to gravity, is one of the main model systems to study the physics of turbulent thermal convection. In this project, we focus on the investigation of the interaction between shear and buoyancy and want to know, how they influence the development of the flow superstructures and contribute to the mean heat transport enhancement in the system.

In the last decades, hydro power plants have experienced a continual extension of the operating range in order to integrate other renewable energy sources into the electrical grid. When operated at off-design conditions, the turbine experiences cavitation which may reduce the power output and can cause severe damage in the machine. Cavitation simulations are necessary to investigate phenomena like the full load instability. The goal of this project is to understand the physical mechanisms that result in an instability at off-design conditions to identify measures that can avoid the occurrence of instability.

Wind turbine and aircraft design relies on numerical simulation. Current aerodynamic models represent turbulence not directly but model its averaged impact. Such models are only reliable near the design point and require vast experience of the design engineer. Industry wants therefore to enable more accurate methods, such as wall-modeled Large-Eddy Simulation (wmLES) which represents turbulent flow structures directly. R2Wall provides a high-resolution simulation of the NACA4412 airfoil as reference data for the development of wall-models for LES and turbulence models in general. This project has enabled the definition of guidelines for future computations, and the calibration of wall-models.

The focus of this project is the direct numerical simulation (DNS) of an evaporating spray in a turbulent channel flow. The complexity of the phenomenon lies in the nonlinear interaction of phase change thermodynamics and turbulent transport mechanisms at a multitude of scales. The recent availability of larger supercomputing power, together with our novel technique to treat efficiently the interface resolved phase change, enables us to perform the first DNS of more than 14k droplets evaporating in turbulent flow, with full coupling of momentum, heat and mass transfer, both intra- and inter-phase.

In this study, researchers in fluid mechanics at ISAE-SUPAERO investigate possible control of shock boundary layer interaction, a well known flow phenomenon occuring on high speed supersonic devices. In particular, low frequency modes have a significant impact on the device load. High fidelity simulations of turbulent flows are performed to understand the modifications of the flow field induced by the microramp vortex generators located upstream the interaction.

Primary goal of this project, run on HPC system SuperMUC of LRZ, was the establishing of a direct numerical simulation (DNS) data base of primary breakup of a liquid jet injected into stagnant air. Due to the wide range of time and length scales the development of a predictive large eddy simulation (LES) framework is highly desirable. However, the multiscale nature of atomization is challenging, as the presence of the phase interface causes additional subgrid scale terms to appear in the LES formalism. DNS provides fully resolved flow fields and flow statistics for a-priori subgrid scale analysis and a-posteriori LES validation.

Sorting is one of the most fundamental and widely used algorithms. It can be used to build index data structures, e.g., for full text search or for various applications in bioinformatics. Sorting can also rearrange data for further processing. In particular, it is a crucial tool for load balancing in advanced massively simulations. The wide variety of applications means that we need fast sorting algorithms for a wide spectrum of situations. Researchers have developed massively parallel robust sorting algorithms, apply new load balancing techniques, and systematically explore the design space of parallel sorting algorithms.

Direct numerical simulation (DNS) has been applied to study the noise emitted by combustion processes. A highly efficient numerical tool based on the public domain code OpenFOAM has first been developed for DNS of chemically reacting flows, including detailed calculations of transport fluxes and chemical reactions. It has then be used to simulate different turbulent flame configurations to gain an insight into the flame-turbulence interaction, which represents the main noise generation mechanisms. Based on the DNS results, simple correlation models have been developed to predict combustion noise by means of unsteady heat release due to turbulent combustion.

Channel flows are important references for studying turbulent phenomena in a simplified setting. The present project investigates Couette flow, i.e. channel flow driven by a moving wall. Although important to many practical applications, Couette flows have been studied considerably less than other canonical flows, for (a) the experimental setup is very complex, and (b) long and wide structures are present which are characteristic to Couette-type flows. This accounts for long and wide computational domains, which make direct numerical simulations of Couette flow expensive. Even by applying permeable boundary conditions, i.e. blowing from the lower and suction from the upper wall, the Couette-type structures could not be destroyed. Instead,…

A cavity in a turbulent gas flow often leads to an interaction of vortex structures and acoustics. By exploiting this interaction, in some applications sound can be suppressed: silencers for jet engines or exhausts. In other cases, sound can be equally produced: squealing of open wheel-bays, sunroof and window buffeting, noise of pipeline intersection and tones of wind instruments. Typically, in expansive experimental runs, various configurations are tested in order to fulfill the design objectives of the respective application. Based on a 'Direct Numerical Simulation', the aim is to improve the understanding of the interactions between turbulence and acoustics of cavity resonators and to develop standalone sound prediction models, which…

Researchers of the Institute of Aerodynamics and Gas Dynamics (IAG) at the University of Stuttgart investigate the aerodynamic behaviour of modern wind turbines by means of CFD, using the finite volume code FLOWer. The main topics of interest are the effects on the turbine loads caused by turbulent inflow conditions and their control by active trailing edge flaps, and the analysis of the complex flow around the nacelle. Additional studies are currently conducted regarding the effects of aero-elasticity and impact of complex terrain.

The project focuses on the one hand on the improvement of flow physics knowledge related to flow separation at highly swept wing leading-edges resulting in large scale vortical structures. The evolution and development of such leading-edge vortices along with inherent instability mechanisms are still hard to be correctly predicted by numerical simulations. Special attention is needed on turbulence modelling and scale resolving techniques enabling also flow control methodologies for such types of flow. On the other hand, aerodynamic features of elasto-flexible lifting surfaces have been studied.

The coalescence of nano-droplets is investigated using the highly optimized molecular dynamics software ls1 mardyn. Load balancing of the inhomogeneous vapor-liquid system is achieved through k-d trees, augmented by optimal communication patterns. Several solution strategies that are available to compute molecular trajectories on each process are considered, and the best strategy is automatically selected through an auto-tuning approach. Recent simulations that focused on large-scale homogeneous systems were able to leverage the performance of the entire Hazel Hen supercomputer, simulating for the first time more than twenty trillion molecules at a performance of up to 1.33 Petaflops.

Researchers of the Insitute of Aerdynamics and Gasdynamics at the University of Stuttgart leverage high-performance computing to analyse the behaviour of helicopters during various states of flight. Investigations range from deep analyses of fundamental aerodynamic phenomena like dynamic stall on the retreating blade to surveys over a broad spectrum of flight states over the full flight envelope of new configurations, to reduce flight mechanical risks. Recently, the group was able to simulate the first robust representation of the so-called tail-shake phenomenon—an interference between the aerodynamic wake of the rotor and upper fuselage and the tail boom with its elastic behaviour.

Using state-of-the-art simulation technology for highly resolved computational fluid dynamics (CFD) solutions, the helicopter and aeroacoustics group at the Institute of Aerodynamics and Gasdynamics at the University of Stuttgart has simulated the complex aerodynamics, aeromechanics, and aeroacoustics of rotorcraft for years. By advancing the established flow solver FLOWer, which now integrates higher order accuracy and systematic concentration of spatial resolution in targeted regions, the IAG-based group was able to obtain results for complete helicopters at certification-relevant flight states within the variance of individual flight tests for the aerodynamic noise.

The generation of clean, sustainable energy from plasma fusion reactors is currently limited by the presence of microinstabilities that arise during the fusion process, despite international efforts such as the ITER experiment, currently under construction in southern France. Numerical simulations are crucial to understand, predict, and control plasma turbulence with the help of large-scale computations. Due to the high dimensionality of the underlying equations, the fully resolved simulation of the numerical ITER is out of scope with classical discretization schemes, even for the next generation of exascale computers. With five research groups from mathematics, physics, and computer science, the SPPEXA project EXAHD has proposed to use a…

In the quest for efficiency enhancement in energy conversion, supercritical carbon dioxide (sCO2) is an attractive alternative working fluid. However, the heat transfer to sCO2 is much different in the supercritical region than the subcritical region due to the strong variation of thermophysical properties which bring the effects of flow acceleration and buoyancy. The peculiarity in heat transfer and flow characteristics cannot be predicted accurately by using conventional correlations or Reynolds-Averaged Naiver-Stokes (RANS) simulations based on the turbulence models. Therefore, direct numerical simulation (DNS) is used in this ongoing project. In DNS, the Naiver-Stokes equations are numerically solved without any turbulence models. For…

This project was part of the ExaFSA project that investigates the possibility to exploit high-performance computing systems for integrated simulations of all parts contributing to noise generation in flows around obstacles. Such computations are challenging, as they involve the interaction of various physical effects on different scales. In this context, the compute time on SuperMUC granted for this project was used to particularly investigate the coupling of the flow within a large acoustic domain with individual discretization methods.

The dynamic behaviour of fluid motion is driven by processes on a wide range of spatial and temporal scales. In a project run by Heidelberg University scientists, parts of model systems that describe fluid dynamics and temperature evolution were investigated. The models are formulated in terms of velocity, temperature, pressure, and density. The researchers employ a hierarchy of different physical models with an increasing degree of complexity. Additionally, uncertain input parameters are taken into account.

The characteristic patterns seen on the solar surface, on gas giants, in Earth's atmosphere and oceans, and many other geo- and astrophysical settings originate from turbulent convection dynamics flows driven by a density difference caused by, for instance, a temperature gradient. Convection in itself is inherently complex, but often it is the interaction with other forces, such as the Coriolis and Lorentz force due to rotation and magnetic fields, that determines the actual shape and behaviour of the flow structures. Understanding these convective patterns is often essentially tantamount to understanding the underlying physics at play. In this project, surveys through the huge parameter space are conducted, to not only categorise flow…

Researchers at the Chair of Turbomachinery and Flight Propulsion (LTF) at the Technical University Munich numerically investigate flow and combustion in rocket engines using “green” propellants. The current focus involves researching methane/oxygen as a propellant combination, promising to be a good replacement for the commonly used hydrazine, offering good performance, storability, and handling qualities, while also being significantly less toxic. The goal of the project is an improved understanding of the relevant physical processes and a reliable prediction of thermal loads on the combustor.

In many turbulent convection flows in nature and technology the thermal diffusivity is much higher than the kinematic viscosity which means that the Prandtl number is very low. Applications of this regime reach from deep solar convection, via convection in the liquid metal core of the Earth to liquid metal batteries for grid energy storage and nuclear engineering technology. Laboratory experiments in low-Prandtl-number convection for Pr < 0.1 have to be conducted in liquid metals which are inaccessible for laser imaging techniques and require analysis by ultrasound or X-rays. Direct numerical simulations of this regime of turbulent convection at high Rayleigh numbers are the only way to reveal the full three-dimensional structure of…

At the Institute of Combustion Technology for Aerospace Engineering (IVLR) of the University of Stuttgart a team of scientists numerically investigates reacting flows at conditions typical for modern space transportation systems. The goal of the project is the better understanding of the ongoing processes in the combustion chambers and an improvement of the thermal load predictions. The research is integrated into the program "Technological Foundations for the Design of Thermally and Mechanically Highly Loaded Components of Future Space Transportation Systems" funded by the DFG.

A research group from the Institute of Aerodynamics (AIA) of the RWTH Aachen University utilized the computing power of Hazel Hen for large-scale simulations to analyze the intricate wake flow phenomena of space launchers. The objective of the project is the fundamental understanding of the origin of so called buffet loads acting on the nozzle which can lead to critical structural damage and to develop flow control devices to increase the efficiency and reliability of orbital transportation systems necessary for the steadily increasing demand for communication and navigation satellites.

This project has investigated the problem of sediment transport and subaqueous pattern formation by means of high-fidelity direct numerical simulations which resolve all the relevant scales of the flow and the sediment bed. In order to realistically capture the phenomenon, sufficiently large computational domains with up to several billion grid nodes are adopted, while the sediment bed is represented by up to a million mobile spherical particles. The numerical method employed features an immersed boundary technique for the treatment of the moving fluid-solid interfaces and a soft-sphere model to realistically treat the inter-particle contacts. The study provides, first and foremost, a unique set of spatially and temporally resolved…

Open channel flow can be considered as a convenient "laboratory" for investigating the physics of the flow in rivers. One open questions in this field is related to the influence of a rough boundary (i.e. the sediment bed) upon the hydraulic properties, which to date is still unsatisfactorily modelled by common engineering-type formulae. The present project aims to provide the basis for enhanced models by generating high-fidelity data of shallow flow over a bed roughened with spherical elements in the fully rough regime. In particular, the influence of the roughness Reynolds number and of the spatial roughness arrangement upon the turbulent channel flow structure is being studied.

This project aims at the simulation of the influence of a turbulent atmospheric boundary layer flow on a wing. For this purpose the compressible flow solver DLR-TAU is used, which is developed by the German Aerospace Center (DLR). For initialising the simulation with a turbulent wind field a method to generate synthetic turbulence is used. This method uses statistics from measured time series from the atmospheric boundary layer to generate a threedimensional turbulent wind field which can be used as initial field in the flow simulations.

In order to significantly reduce the drag and the environmental impact of future aircraft, considerable effort has to be undertaken in all fields of aircraft design. Besides reducing drag around the cruise condition of typical transport aircraft, it is also of great interest to expand the flight envelope in order to allow for a more flexible design. Understanding the behaviour of a commercial transport aircraft at the limits of its flight envelope, away from its design point, requires either expensive flight testing, tests in sophisticated wind tunnel facilities or advanced computational models. As flight tests are very expensive and take place in a late phase during the development of a new aircraft, when most of the design is already…

The subject of multiphase flows encompasses many processes in nature and a broad range of engineering applications such as weather forecasting, fuel injection, sprays, and the spreading of substances in agriculture. To investigate these processes the Institute of Aerospace Thermodynamics (ITLR) uses the direct numerical simulation (DNS) in-house code Free Surface 3D (FS3D). The code is continually optimized and expanded with new features and has been in use for more than 20 years. Investigations were performed, for instance, for phase transitions like freezing and evaporation, basic drop and bubble dynamics processes, droplet impacts on a thin film (“splashing”), and primary jet breakup as well as spray simulations, studies involving…

The reduction of aeroacoustic noise emissions from technical systems like wind turbines or airplanes is a today’s key research goal. Understanding the intricate interactions between noise generation and flow field requires the full resolution of all flow features in time and space. Thus, very highly resolved unsteady simulations producing large amounts of data are required to get insight into local noise generation mechanisms and to investigate ideas for reduction. These mechanisms have been investigated by researchers at the University of Stuttgart through direct numerical simulation (DNS) of a generic airfoil configuration on Hazel Hen at HLRS. The results help to understand noise generation from turbulent flows and also serve as a…

The Institute of Space Systems (IRS) and the Institute of Aerodynamics and Gas Dynamics (IAG) at the University of Stuttgart cooperatively develop the particle simulation tool "PICLas", a flexible simulation suite for the computation of three-dimensional plasma flows. The tool enables the physically-accurate numerical simulation of non-equilibrium plasma and gas flows. The applications range from the atmospheric entry of spacecraft to laser-plasma interaction in material sciences. The high-fidelity numerical approach allows detailed insights in the physical phenomena and is made feasible by high-performance computing.

Researchers carry out numerical simulations of spray painting processes using a commercial high-speed rotary bell atomizer within the frame of an ongoing project “smart spray painting process”. Using a commercial CFD-code, detailed numerical studies deal with the film formation of the paint liquid on the bell cup, the primary liquid breakup near the bell edge, the paint droplet trajectories, as well as the droplet impact onto solid surface. Simulation results deliver important information for understanding and optimization of the complicated spray painting processes.

Understanding the nature of the turbulent flow mixing behavior in power plants which induce thermal fatigue cracking of components is still an unresolved challenge. Aside from measurements being performed at realistic power plant conditions (e.g. at 8 MPa pressure and temperature difference of 240°C between the mixing fluids) numerical calculations involving high-performance computing could throw more light into the complex fluid flow at any location of interest to investigators. Thus a combination of measurements coupled with numerical calculations could positively contribute towards realistic assessment of thermal fatigue damage induced in power plant components.

Viscosity represents the most important property of turbulent flows, yet its impact of its variation on turbulence dynamics is not yet fully understood. This project addresses how the dissipation mechanism and self-similarity of turbulent flows are affected by fluctuations in viscosity—questions that can help lead to better turbulent mixing models, and, in turn, improved predictions of pollutants in combustion engines. Highly resolved direct numerical simulations of turbulent shear flows on JUQUEEN with up to 231 billion grid points were performed in pursuit of an answer to this question.

Noise reduction is a key goal in European aircraft policy. One of the major noise sources at aircraft take-off is the engine jet noise. Recently, chevron nozzles were introduced which have drawn a lot of attention in research and the aircraft industry. Since the flow structures in the jet depend on the details of the nozzle exit geometry and have a large impact on the noise sources in the jet, scientists of the RWTH Aachen University extensively investigate chevron nozzles by running large-scale simulations based on a highly resolved mesh with up to 1 billion mesh cells.

With the rapidly changing massively parallel computer architectures arising in recent years, it became a huge challenge to make efficient use of contemporary supercomputers. Project ExaStencils addresses this problem by providing an easy-to-use, multi-layered domain-specific language to the application programmer such that problems can be formulated in an intuitive way fitting to different levels of abstraction. The necessary code transformations are performed by a special-purpose compiler framework that is able to produce scalable and efficient code that runs on large supercomputers like JUQUEEN of JSC.

Wind turbines are becoming increasingly efficient and quieter, while turbines operate reliably at high pressures and temperatures, and aircrafts use less fuel. These and other technical advances are made possible in great part because the occurring flow fields can be simulated with great accuracy on modern supercomputers. These machines use one hundred thousand processors and more to perform their calculations. The programs that are to run on such devices must be adapted to this high number of processors. An interdisciplinary team, which includes researchers of several institutes of the University of Stuttgart, has developed such a software package to enable two-phase flow simulations, where gaseous and liquid phases coexist. 

Supersonic impinging jets can be found in different technical applications of aerospace engineering. Depending on the flow conditions, loud tonal noise can be emitted. The so-called impinging tone is investigated by researchers of the chair of computational fluid dynamics at the Technical University of Berlin. Using direct numerical simulations (DNS) carried out on the Cray HPC systems Hermit, Hornet and Hazel Hen of the HLRS, the underlying sound source mechanisms could be identified for a typical configuration.

The flow layer near the surface of a body - the boundary layer - can have a smooth, steady, low-momentum laminar state, but also an unsteady, turbulent, layer-stirring state with increased friction drag and wall heat flux. Wall heating is especially severe with supersonic hot gas flows like, e.g., in a rocket (Laval-) nozzle extension. To protect the walls from thermal failure a cooling gas is injected building a cooling film. Its persistence depends strongly on the layer state of the hot-gas flow, the type of cooling gas, and the form and strength of injection. Fundamental studies are performed using direct numerical simulations, providing also valuable benchmark data for less intricate computational-fluid-dynamics methods using turbulence…

As part of the collaborative research centre CRC 1029, impingement cooling is studied at the chair of computational fluid dynamics at the Technical University of Berlin. The project aims at a more efficient cooling of turbine blades. This is necessary since future combustion concepts within gas turbines bring much higher thermal loads. Large scale direct numerical simulations (DNS) are carried out using the Cray supercomputers Hermit, Hornet and Hazel Hen of the HLRS.

As an integral part of the PRACE SHAPE project HPC Welding, the parallel solvers of the Finite Element Analysis software LS-DYNA were used by Ingenieurbüro Tobias Loose to perform a welding analysis on HLRS HPC system Hazel Hen. A variety of test cases relevant for industrial applications had been set up with DynaWeld, a welding and heat treatment pre-processor for LS-DYNA, and were run on different numbers of compute cores to test its scaling capabilities.

Researchers at the Institute of Combustion Technology at the German Aerospace Center (DLR) use petascale HPC system SuperMUC at LRZ in Munich for the simulation of soot evolution in lifted, turbulent, ethylene-air jet flames. The scope of their work is to develop and analyze simulation techniques for turbulent combustion with focus on soot predictions. The long-term objective is to develop validated high fidelity simulation techniques for soot predictions in turbulent combustion systems such as aeroengines.

The project EXASTEEL is concerned with parallel implicit solvers for multiscale problems in structural mechanics discretized using finite elements. It is focussed on modern high strength steel materials. The higher strength and better ductility of these materials largely stems from the carefully engineered grain structure at the microscale. The computational simulations used therefore take into account the microstructure, but without resorting to a brute force discretization (which will be out of reach for the foreseeable future). The researchers' approach combines a computational multiscale approach well known in engineering (FE) with state-of-the-art parallel scalable iterative implicit solvers developed in mathematics. 

The direct numerical simulation performed in the course of this project – run on SuperMUC at LRZ – investigated a temporally evolving non-premixed syngas jet flame. Results of this simulation were used to validate a recently published set of extended model equations for the reaction zone dynamics in non-premixed combustion. Furthermore, the dataset was used to analyze the importance of curvature induced transport phenomena. Regions could be identified where curvature has a significant impact on the flame structure.

The interaction between a turbulent flow field and light-weight structural systems is the main topic of the present research project aiming at the development of advanced computational methodologies for this kind of multi-physics problem denoted fluid-structure interaction (FSI). This should allow to predict these complex coupled problems more reliably and to get closer to reality. An original computational methodology based on advanced techniques on the fluid and the structure side has been developed especially for thin flexible structures in turbulent flows.

Spray evaporation and burning in a turbulent environment is a configuration found in many practical applications, such as diesel engines, direct-injection gasoline engines, gas turbines, etc. Understanding the physical process involved in this combustion process will help improving the combustion efficiency of these devices and, therefore, reduce their emissions. Direct numerical simulation (DNS) is a very attractive tool to investigate in all details the underlying processes since it is able to capture and resolve all scales in the system. In this project, evaporation, ignition, and mixing are investigated in both temporally- and spatially-evolving jets, using DNS.

In many turbulent convection flows in nature and technology the thermal diffusivity is much higher than the kinematic viscosity which means that the Prandtl number is very low. Laboratory experiments in very low-Prandtl-number convection have to be conducted in liquid metals which are inaccessible for laser imaging techniques and require analysis by ultrasound or X-rays. Researchers of the TU Ilmenau and the Occidental College Los Angeles ran direct numerical simulations of this regime of turbulent convection at high Rayleigh numbers to reveal the full 3D structure of temperature and velocity fields.

The electro-dialysis process is an efficient desalination technique that uses ion exchange membranes to produce clean water from seawater. This process involves different physical phenomena like fluid dynamics, electrodynamics and diffusive mass-transport along with their interactions. Rigorous assessment of those interactions, especially those near the membranes, are only possible through large-scale coupled simulations. The aim of the APAM compute time project is the detailed flow simulation in this application to understand the effect of different spacer structures between the membranes in this process.

A numerical research project, run on Hornet of HLRS, focused on the grid of internal combustion (IC) engines in the vicinity of the intake valve and its effect on the simulation results. The overall goal was to develop a methodology for a quantitative comparison of different results in terms of the intake jet as well as the identification of crucial mesh regions.

In the last decades, hydraulic machines have experienced a continual extension of the operating range in order to integrate other renewable energy sources into the electrical grid. When operated at off-design conditions, the turbine experiences cavitation which may reduce the power output and can cause severe damage in the machine. Cavitation simulations are suitable to give a better understanding of the physical processes acting at off-design conditions. The goal of this project is to give an insight in the capabilities of two-phase simulations for hydraulic machines and determine the range for safe operation.

The operation range of hydraulic turbines is increasing more and more to guarantee the power system stability of the electric grid due to the increased amount of electric power generated by unregulated renewable energy like wind and photovoltaic. Therefore, hydraulic turbines are operated in off-design conditions where highly transient phenomena can occur. Standard approaches which are used for the design process of hydraulic machines are no longer suitable to predict the correct flow field in these operating points. Advanced turbulence models and high mesh resolutions are applied to increase the accuracy of the simulations.

A project carried out by a team of scientists from the Institute of Aerodynamics and Fluid Mechanics at the Technische Universität München focused on the numerical investigation of cavitating flow in the context of ship propellers. A key aspect of this project was to develop the ability to assess local flow aggressiveness and to quantify the potential of material erosion.

Rayleigh-Benard flow (the flow in a box heated from below and cooled from above) and Taylor-Couette flow (the flow between two counter-rotating cylinders) are the two paradigmatic systems in the physics of fluids, and many new concepts have been tested with them. Researchers from the Physics of Fluids group at the University of Twente have been carrying out simulations of these systems on HLRS supercomputers to try and improve our understanding of turbulence.

Researchers leveraged the computing power of SuperMUC for the development of finite volume Lagrangian numerical schemes on multidimensional unstructured meshes for fluid dynamic problems. The numerical algorithms developed in project STiMulUs are designed to be high order accurate in space as well as in time, requiring even more information to be updated and recomputed continuously as the simulation goes on.

Despite the great success of current state-of-the-art fluid flow solvers, the continuing development of computing hardware necessitates new numerical methods for flow simulations. High order methods on unstructured grids like Discontinuous Galerkin discretisations deliver highly accurate results and allow for unprecedented parallelisation efficiency at huge numbers of cores. The project aims to transfer the infrastructure technology (overlapping Chimera grids, mesh movement and deformation, convergence acceleration) from conventional to such advanced solvers to allow application to relevant engineering problems like helicopter simulations in the mid-term future.

The helicopter and aeroacoustics group of IAG runs extensive aerodynamics and aeromechanics simulations of rotorcraft in order to understand not only basic parameters as power requirements or loads on the rotor blades but also to predict acoustic footprints and gain a deeper insight into the interactions between different helicopter components. For this purpose, the group runs simulation setups on HLRS supercomputer Hazel Hen of a magnitude beyond 200 million cells with fifth order accuracy and even up to half a billion cells for selected cases, delivering results directly comparable to real flight test data at unparalleled accuracy.

The project Investigation of Delta Wing Time Dependent Flow Characteristics with Lattice-Boltzmann Method is carried out by the Technische Hochschule Ingolstadt, Faculty of Mechanical Engineering, at the High Performance Computing Center Stuttgart. It focuses on the numerical investigation of the delta wing flow under various aspects such as sweep angle variation, sharp or round leading edges, as well as high and lower Reynolds numbers with a Lattice-Boltzmann PowerFLOW solver provided by Exa.

An international research project aimed at investigating the structure and dynamics of wall-bounded turbulence in adverse pressure gradient environments has resulted in the first Direct Numerical Simulation (DNS) of a self-similar turbulent boundary layers (TBL) in a strong adverse pressure gradient (APG) environment at the verge of separation up to a Reynolds number based on the momentum thickness of 10⁴.

Turbulent flow seeded with solid particles is encountered in a number of natural and man-made systems. Many physical effects occurring when the fluid and the solid phase interact strongly so far have obstinately resisted analytical and experimental approaches – sometimes with far reaching consequences in various practical applications. Using SuperMUC, researchers simulated with unprecedented detail the turbulent flow in an unbounded domain in the presence of suspended, heavy, solid particles in order to understand and describe the dynamics of such particulate flow systems with sufficient accuracy.

Researchers investigated the mechanism of secondary flow formation in open duct flow where rigid/rigid and mixed (rigid/free-surface) corners exist. Employing direct numerical simulations (DNS) on HLRS high performance computing system Hornet, the scientists aimed at generating high-fidelity data in closed and open duct flows by means of pseudo-spectral DNS and at analysing the flow fields with particular emphasis on the dynamics of coherent structures.

Leveraging the petascale computing power of HPC system JUQUEEN of the Jülich Supercomputing Centre, researchers at the Chair of Computational Science at ETH Zurich performed unprecedented large-scale simulations of cloud cavitation collapse with up to 75’000 vapor cavities on resolutions of up to 0.5 trillion mesh cells and 25’000 time steps.

In order to gain a deeper understanding of the aerodynamic noise generation mechanisms and transmission for automotive applications, researchers from the Universität Erlangen leveraged HPC system SuperMUC of LRZ to develop a hybrid aeroacoustic method. The turbulent flow over a forward-facing step served as a test case for the final validation of a hybrid scheme for the computation of broadband noise, as caused typically by turbulent flows.

Researchers of the Technische Universität München conducted large-eddy simulations (LES) on HPC system SuperMUC of LRZ for numerical investigations of a pseudo-shock system. These pseudo-shock systems influence the reliability and performance of a wide range of flow devices, such as ducts and pipelines in the field of process engineering and supersonic aircraft inlets. Thus, the optimization of pseudo-shock systems is of great academic and commercial interest.

Shock-wave/boundary-layer interactions (SBLIs) play an important part in many engineering applications. They are common in internal and external aerodynamic flows. However, numerical treatment of such SBLIs is difficult as the important flow features place competing demands on the applied numerical algorithms. Using the HPC infrastructure provided by the HLRS, scientists of the Technische Universität Berlin performed a detailed direct numerical simulation of a transonic SBLI creating a detailed numerical database this way which is now available for further detailed studies.

Within the framework of a research project which aims at reducing the emission of CO₂ by conventional coal-fired power plants through oxy-fuel combustion, scientists of the RWTH Aachen University simulated the heating processes of coal dust in order to gain a better understanding of the conditions causing carbon dust to ignite in an oxygen-carbon dioxide atmosphere. Since carbon particles are of irregular, non-spherical shape their motion is difficult to predict, thus simulations of large quantities of fully dissolved carbon particles moving freely in a turbulent flow require the availability of petascale HPC systems like Hazel Hen.

Fluid-Structure Interaction is a topic of major interest in many engineering fields. The significant growth of the computational capabilities allows solving more complex coupled problems, whereby the physical models get closer to reality. In order to simulate practically relevant light-weight structural systems in turbulent flows, scientists of the Helmut-Schmidt-University in Hamburg developed and implemented an original computational methodology especially for thin flexible structures in turbulent flows.

This project, for which HPC system Hermit of the High Performance Computing Center Stuttgart served as computing platform, is part of the NURESAFE initiative for nuclear safety. The objective was to develop a global modelling framework for multi-scale core thermal-hydraulics in Pressurized Water Reactors (PWR) as understanding heat transfer phenomena in turbulent bubbly flows is of great interest for the scientist community and for the industry.

In order to analyse aeroacoustic noise generation processes, researchers from the Institute for Aerodynamics and Gas Dynamics performed high fidelity, large-scale flow and acoustic computations using the discontinuous Galerkin spectral element method on the HPC system Hornet at the High Performance Computing Center Stuttgart (HLRS). The aim of this investigation is to gain insight into the tonal noise generation process of a side-view mirror.

A scramjet is an air breathing jet engine for hypersonic flight velocities of about ten to twenty times the speed of sound. Combustion, too, takes place at supersonic flow velocity, which requires a fast mixing of fuel and compressed airflow to enable combustion during the very short residence time of the reactants in the combustion chamber. To analyze the flame stabilization in the combustion chamber through a pilot injection of hydrogen and air at the base of the strut injector, researchers from the Technische Universität München (TUM) performed large-eddy simulations for a generic strut-injector geometry based on an experimental setup at the TUM.

Researchers of the University of Erlangen applied the waLBerla Framework, a widely applicable lattice Boltzmann simulation code, on HPC system SuperMUC of LRZ to test the suitability of the software framework for different Computational Fluid Dynamics applications: One project focused on investigating collective swarming behavior of numerous self-propelled microorganisms at low Reynolds numbers, a second project implemented within waLBerla was the simulation of electron beam melting, while a third simulated the separation of charged macromolecules in electrolyte solutions inside channels of dimensions relevant for lab-on-a-chip (LoC) systems.

Direct numerical simulation (DNS) of turbulent mixing layers has been possible only in relatively recent times. In an ambitious project using HPC system JUQUEEN of JSC, scientists analysed the process of mixing layer formation in a flow configuration with sizeable compressibility effects by numerically reproducing the flow conditions of a well documented flow case with two turbulent streams. Large-scale direct numerical simulation were performed in a wide computational domain which included the two upstream turbulent boundary layers developing on the two sides of a zero-thickness splitter plate and their early merging region. The complexity of the flow, the extent of the computational box and the mesh size made the study extremely…

Scientists of the Institute of Aerodynamics and Gas Dynamics of the University of Stuttgart conducted a Direct Numerical Simulation of a spatially-developing supersonic turbulent boundary layer up to Re_Θ=3878. For this purpose, they used the discontinuous Galerkin spectral element method (DGSEM), a very efficient DG formulation that is specifically tailored to HPC applications. It allowed the researchers to efficiently exploit the entire computational power available on the HLRS Cray XC40 supercomputer Hornet and to run the simulation with 93,840 processors without any performance losses. 

A research team of the Institute of Aerodynamics (AIA) of the RWTH Aachen University leveraged the petascale computing power of the HPC system Hornet for large-scale simulation runs which used the entirety of the system’s available 94,646 compute cores. The project “Large-Eddy Simulation of a Helicopter Engine Jet” aimed at analysing the impact of internal perturbations due to geometric variations on the flow field and the acoustic field of a helicopter engine jet. For this purpose, the researchers conducted highly resolved large-eddy simulations based on hierarchically refined Cartesian meshes up to 1 billion cells over a time span of 300 hours.

Exploiting the available computing capacities of supercomputer Hornet of the High Performance Computing Center Stuttgart, researchers from the Institute of Aerodynamics (AIA) of the RWTH Aachen University conducted a large-scale simulation run in their efforts to tackle the prediction of the acoustic field of a low pressure axial fan using computational aeroacoustics (CAA) methods. Goal of this project, which scaled to 92,000 compute cores of the HPC system Hornet, was to achieve a better understanding of the development of vortical flow structures and the turbulence intensity in the tip-gap of a ducted axial fan.

A research team of the Institute of Simulation Techniques and Scientific Computing of the University of Siegen leveraged the petascale computing power of HPC system Hornet for their research project Ion Transport by Convection and Diffusion. This large-scale simulation project stressed the available capacities of the HLRS supercomputer to its full extent as the simulation involved the simultaneous consideration of multiple effects like flow through a complex geometry, mass transport due to diffusion and electrodynamic forces. Goal of this project was to achieve a better understanding of the electrodialysis desalination process in order to identify methods and possibilities of how to optimize it.

A research project addressed the fundamental mechanisms and processes involved in the dynamics of a large number of rigid particles settling under the influence of gravity in an initially quiescent fluid, as well the characteristics of the particle-induced flow field.

One of the major limiting factors of the flight operational range of transport aircraft is the inlet separation of engine. The overall aim of this project is to provide an efficient numerical method able to compute the large range of spectral scales present in flows during the separation process.

For delta and diamond wing configurations, the flow field is typically dominated by large scale vortex structures, which originate from the wing leading-edges. With increasing angle of attack, the flow structures grow in size and become more and more unsteady. By use of active and passive flow control mechanisms, the vortex characteristics can be manipulated and controlled in some extent.

Scientists of the University of Rome (“Tor Vergata”) and the University of Eindhoven aimed to perform a systematic investigation of multi-component and/or multi-phase flow dynamics in porous matrices adopting a bottom-up, multi-scale approach based on a Lattice Boltzmann Method (LBM).

Scientists of the Technische Universität Braunschweig conduct Direct Navier-Stokes (DNS) and Large Eddy Simulation (LES) computations of turbulent flows which explicitly take into account specific pore scale geometries obtained from computer tomography imaging and do not use any explicit turbulence modeling.

With the projected demand for air transport set to double the world aircraft fleet by 2020 it is becoming urgent to take steps to reduce the environmental impact of take-off noise from aircraft. Scientists from the UK performed highly intensive Large Eddy Simulations (LES) of complex geometry jets with the major emphasis to use the LES CFD approach (Computational Fluid Dynamics) to enable improved prediction and to generate the necessary complex unsteady flow fields needed for acoustic modelling.

Modern Diesel injection systems exceed injection pressures of 2000 bar in order to meet current and future emission regulations. By accelerating the flow through an injection nozzle or throttle valve pressure in the liquid can drop below vapor pressure, initiating local evaporation (hydrodynamic cavitation). The advection of vapor cavities into regions where the static pressure of the surrounding liquid exceeds vapor pressure leads to a sudden re-condensation or collapse of vapor cavities. The surrounding liquid is accelerated towards the center of the cavities and strong shock waves are emitted. The resulting pressure loads can lead to material erosion. For optimization of future fuel injectors the ability to predict cavitation and…

An international team of scientists conducted high-precision spectral element simulations which resolved the fine-scale structure of turbulent Rayleigh-Bénard convection, in particular the statistical fluctuations of the temperature and velocity gradients.

A team of scientists from Germany, UK, US and Spain have developed a multiscale particle methods framework based on Smoothed Particle Hydrodynamics (SPH) and the stochastic Smoothed Dissipative Particle Dynamics (SDPD) to simulate the complex dynamics of submicron-sized colloidal and large non-colloidal particles suspended in Newtonian and non-Newtonian fluids.

Liquid chromatography is an industrially relevant application of mass transport through a porous medium, where a fluid mix of chemical substances is separated into its components by passing through a cylindrical tube densely packed with solid, spherical adsorbent particles (the column). The number of chemical substances that can be separated by a column (its separation efficiency) is determined by how the packing particles are distributed over the column volume. 

A team of scientists of the Institute of Aerodynamics and Fluid Mechanics of the Technische Universität München have developed a smoothed particle hydrodynamics (SPH) method to simulate complex multiphase flows with arbitrary interfaces and included a model for surface active agents (surfactants) [1]. In SPH the computational domain is discretized with particles that are moving in time.

Aircraft engines are equipped with airblast atomizers to assure the liquid fuel injection. During airblast atomization a thin liquid film is passed by coflowing air streams, leading to the disintegration of the liquid sheet. The breakup process is still not well understood, especially a detailed insight into the phenomena of primary breakup is a major limitation in understanding these flow systems. In this project the primary breakup of airblasted liquid sheets is investigated numerically. Highly resolved Direct Numerical Simulations (DNS) of this two-phase flows are performed on the GCS Supercomputer SuperMUC at Leibniz Supercomputing Centre.

The process in which a magnetic field is amplified by the flow of an electrically conducting fluid such as liquid metal or plasma, known as dynamo action, is believed to be the origin of magnetic fields in the universe including the magnetic field of the earth. Laboratory experiments using liquid sodium try to investigate the underlying mechanisms. Especially one setup has been successful in producing a dynamo with a free turbulent flow, the Von Karman Sodium experiment in Cadarache, consisting of a cylindrical vessel filled with liquid sodium, stirred by two counter-rotating soft-iron impellers.

The noise emitted from turbulent combustion belongs, similarly to the pollutant emissions, to the negative effects of combustion processes, i.e. noise pollution. The project’s main objective is to analyse in-depth the formation mechanism of noise generated from turbulent flames and to predict such noise radiations already during the development phase. 

It is well known that in order to fulfil the stringent demands for low emissions of NO_x, the lean premixed combustion concept is commonly used. However, lean premixed combustors are susceptible to thermo acoustic instabilities driven by the combustion process and possibly sustained by a resonant feedback mechanism coupling pressure and heat release. This resonant feed back mechanism creates pulsations typically in the frequency range of several hundred Hz and which reach high amplitudes so that the system has to be shut down or is even damaged. Although the research activities of the recent years have contributed to a better understanding of this phenomenon the underlying mechanisms are still not well enough understood.

The accurate simulation and modeling of turbulent fluid motion is a very important research subject in natural and engineering sciences. Ranging from the application in aircraft design, the aeroacoustic optimization of an automobile and the cooling of modern microprocessor devises, the efficient simulation of turbulence is a key technology in modern engineering and design of technical products and devices.

Turbulence is pervasive in turbomachinery, and predicting its effect on the flow and performance is a major challenge for CFD (Computational Fluid Dynamics) tools. RANS (Reynolds-averaged Navier–Stokes) methods, modelling the averaged impact of turbulence, are currently the industrial standard. Scale-resolving approaches such as DNS (Direct Numerical Simulation) and LES (Large Eddy Simulation) compute either all turbulent structures directly, or only represent the larger, and model the impact of the smallest structures. 

Turbulent thermal convection is of fundamental interest in many fields of physics and engineering. Examples to mention here are the convective flows in the Earth’s atmosphere and oceans, in its core and mantle, but also in the outer layer of stars, in chemical engineering or in aircraft cabins. Frequently, these systems are also strongly influenced by rotation.

Turbulence is a flow regimen which is dominated by a wide range of length and time scales. The largest scale of motion depends on the geometry of the problem and the smallest scale of motion on the material properties of the liquid. In the atmosphere the largest scales of motion can be a few hundred kilometers big while the smallest scale of motion are a few millimeters. In an engineering application the largest scales of motion are much smaller than in the atmosphere but still there is a very big difference between the smallest and largest scale of motion. 

Understanding the mechanisms involved in the turbulent transition in boundary layers is crucial for many engineering domains. The instabilities that develop in to those flows are highly non-linear and unsteady. They are mainly studied by analytical theories supplemented by direct numerical simulations (DNS) of the entire flow dynamics which must be sufficiently accurate to properly take into account all spatial and temporal characteristic scales and their non-linear interactions.

Noise prediction is one of the most discussed topics for Computational Fluid Dynamics today due to the fact that noise optimization, energy saving and pollutant emission minimization complement each other. In a GCS Large Scale project headed by Professor Jörn Sesterhenn of the Technische Universität Berlin, numerical simulations of a supersonic jet were performed on HPC system SuperMUC of LRZ, focusing on the research of the acoustic field.

The operation of the flying observatory SOFIA (Stratospheric Observatory For Infrared Astronomy), which was designed to look at celestial bodies in the infrared range of the electromagnetic spectrum from the lower stratosphere above the obscuring water vapor, presents some challenging aerodynamic and aero-acoustic problems.

At the Institute of Combustion Technology for Aerospace Engineering (IVLR) at the University of Stuttgart a team of scientists numerically investigates reacting flows at conditions typical for modern space transportation systems. The research is integrated into the programs SFB/TRR-40 (Technological Foundations for the Design of Thermally and Mechanically Highly Loaded Components of Future Space Transportation Systems) and GRK 1095/2 (Aero-Thermodynamic Design of a Scramjet Propulsion System) that are funded by the DFG (Deutsche Forschungsgemeinschaft).

As an unavoidable consequence of lift, aircraft generate a pair of counter-rotating and persistent wake vortices that may pose a potential risk to following aircraft. The highest risk to encounter wake vortices prevails in ground proximity, where the vortices cannot descend below the glide path but tend to rebound due to the interaction with the ground surface. 

To increase the efficiency and reduce the pollutant emissions of combustion engines, researchers simulate the complex flow field in internal combustion engines which has significant influence on the formation of the fuel-air-mixture in the combustion chamber and on the combustion process itself.

Today, hydropower is the most important and widely used renewable energy source. Due to the strong increase of fluctuating renewable energies, a great amount of regulating power is necessary in the net, which is mainly available from hydropower. As a consequence, the hydraulic turbines are very often operated in extreme off-design conditions.

A team of scientists from the Institute of Aerodynamics and Gas Dynamics of University of Stuttgart are performing direct numerical simulations and sophisticated stability analyses with regard to the so-called hypersonic flight, i.e.with the goal to be able to accelerate an aircraft to at least about five times the speed of sound.

Laminar Turbulent Transition in Aerodynamics Boundary Layers: Scientists from the Institute of Aerodynamics and Gas Dynamics of University Stuttgart are doing simulations on GCS supercomputers to achieve a comprehensive understanding of three-dimensional dynamic instability processes, which is a pre-requisite for successful Laminar Flow Control (LFC).

Project ‘Development and Validation of Thermal Simulation Models for Li-Ion Batteries in Hybrid and Pure Electric Vehicles’ (asc(s, Battery Design, CD-adapco, Daimler AG, Opel AG and Porsche AG) concentrates on the development of a simulation environment for the electro-thermal layout of a lithium ion battery module in a vehicle. The project team pursues the development of optimized design concepts for electrified vehicles to fulfill increasing demands on energy consumption, driving range, and durability.

Delta wings, or wings with a triangular planform, are an important reference configuration for applied high-performance aerodynamics as well as for basic fluid mechanics studies.

Laser ablation is a technology which gains increasingly more importance for drilling, welding, structuring and marking of all kind of materials. Molecular dynamics simulations contribute to new insight into the not completely comprehended ablation process with the short femto second laser pulses.