ENGINEERING AND CFD

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.

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.

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.

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.

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.

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.

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.

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.

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.

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…

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.

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.

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.

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. 

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…

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.

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.

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.

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. 

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).

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).

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.