COMPUTATIONAL AND SCIENTIFIC ENGINEERING

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.

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.

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.

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.

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.

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.

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.

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 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.

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 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.

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.

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.

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,…

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.

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 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.

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.

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 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.

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.

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.

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.

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.

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.

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.

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.

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…

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.

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.

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.

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.

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. 

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.