Computational and Scientific Engineering

(Image: HLRS)

HPC technologies enable researchers to accelerate research and development in industrial processes. Simulation and modelling allow researchers to shorten time-to-market for new products, while also providing new insights into older technologies for power generation, air travel, and urban planning, among others.

The following is a list of recent reports submitted by users of HLRS's high-performance computing systems describing their scientific interests and research results.

Click on each title for a more detailed report. The complete reports are found on the website of the Gauss Centre for Supercomputing (GCS), the alliance of Germany's three national supercomputing centers.

Flow Control using Convergent-Divergent Riblets, a Type of Bio-Inspired Micro-Scale Surface Patterns
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.
Principal Investigator: Jian Fang
Affiliation: Scientific Computing Department, STFC Daresbury Laboratory, UK

Finite-size Particle Dynamics and Scalar Transport in Turbulent Open Channel Flow Over a Mobile Sediment Bed
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.
Principal Investigator: Markus Uhlmann
Affiliation: Institute for Hydromechanics, Karlsruhe Institute of Technology (KIT)

MALEDRAG - Machine Learning Optimisation for Drag Reduction in a Turbulent Boundary Layer
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.
Principal Investigator: Sylvain Laizet
Affiliation: Imperial College London, United Kingdom

CARo – Computational Aeroacoustics of Rotors
Helicopters and other rotorcraft like future air taxis generate substantial sound, placing a noise burden on the community. Advanced simulation capabilities developed at IAG over the last decades enable the prediction of aeroacoustics together with aerodynamics and performance, and thus allow an accurate and reliable assessment of different concepts long before first flight. Consequently, this technology serves to identify promising radical configurations initially as well as to further optimize designs decided on at later stages of the development process. Conventional helicopters may benefit from these tools as much as breakthrough layouts in the highly dynamic Urban Air Mobility sector.
Principal Investigator: Manuel Keßler
Affiliation: Institute of Aerodynamics and Gasdynamics, University of Stuttgart

When Porous Media Meets Turbulence
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.
Principal Investigator: Xu Chu, Bernhard Weigand
Affiliation: Institut für Thermodynamik der Luft- und Raumfahrt, Universität Stuttgart

Revealing the Dynamics of Flames by Tracking Material Points in Highly Resolved Simulations
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.
Principal Investigator: Feichi Zhang
Affiliation: Engler-Bunte-Institute, Karlsruhe Institute of Technology

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.
Principal Investigator: Dr. Manuel Keßler
Affiliation: Institute of Aerodynamics and Gas Dynamics, University of Stuttgart

Active Friction Drag Reduction in Turbulent Boundary Layer Flow
A new active surface actuation technique to reduce the friction drag of turbulent boundary layers is applied to the flow around an aircraft wing section. Through the interaction of the transversal traveling surface wave with the turbulent flow structures, the skin-friction on the surface can be considerably reduced. Highly-resolved large-eddy simulations are conducted to investigate the influence of the surface actuation technique on the turbulent flow field around an airfoil at subsonic flow conditions. The active technique, which previously was only tested in generic scenarios, achieves a considerable decrease of the airfoil drag.
Principal Investigator: Matthias Meinke
Affiliation: Chair of Fluid Mechanics and Institute of Aerodynamics, RWTH Aachen University

Direct Numerical Simulations of Compressible Turbulent Boundary Layers
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.
Principal Investigator: Ulrich Rist, Markus Kloker, Christoph Wenzel
Affiliation: Institute of Aerodynamics and Gas Dynamics, University of Stuttgart

Direct Numerical Simulation of an Impinging Jet at Re=10,000
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.
Principal Investigator: Franco Magagnato
Affiliation: Institute of Fluid Mechanics, Karlsruhe Institute of Technology

Compressible Multi-Phase Flow at Extreme Ambient Conditions
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).
Principal Investigator: Claus-Dieter Munz
Affiliation: Institute of Aerodynamics and Gas Dynamics, University of Stuttgart

Towards the Simulation of the Flow Phenomena at a Helicopter Rotor Using a High-order Method
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.
Principal Investigator: Manuel Keßler
Affiliation: Institute of Aerodynamics and Gas Dynamics, University of Stuttgart

Uncertainty Quantification in Direct Noise Computations of Cavity Feedback
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.
Principal Investigator: Andrea Beck(1), Claus-Dieter Munz(1), Christian Rohde(2)
Affiliation: (1) Institute of Aerodynamics and Gas Dynamics, University of Stuttgart, (2) Institute of Applied Analysis and Numerical Simulation, University of Stuttgart

Wall-Resolved Large Eddy Simulation of Complex Flows in Turbomachines
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.
Principal Investigator: Andrea Beck, Claus-Dieter Munz
Affiliation: Institute of Aerodynamics and Gas Dynamics, University of Stuttgart

Numerical Simulation of Impinging Jets
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.
Principal Investigator: Jörn Sesterhenn
Affiliation: Institut für Strömungsmechanik und Technische Akustik, Technische Universität Berlin

Large Eddy Simulation of a Complete Francis Turbine
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.
Principal Investigator: Timo Krappel
Affiliation: Institute of Fluid Mechanics and Hydraulic Machinery, University of Stuttgart

Shock-related Buffeting in Aeroplanes
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.
Principal Investigator: Neil Sandham
Affiliation: Faculty of Engineering and Physical Sciences, University of Southampton (U. K.)

Numerical Simulation of Primary Break-up in Spray Painting Processes
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.
Principal Investigator: Qiaoyan Ye and Bo Shen
Affiliation: Fraunhofer Institute for Manufacturing Engineering and Automation, Stuttgart

Simulation of Turbulent Flows Interacting with Non-Spherical Particles
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.
Principal Investigator: Wolfgang Schröder
Affiliation: Institute of Aerodynamics, RWTH Aachen University (Germany)

Fully Resolved Autoigniting Transient Jet Flame Simulation
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.
Principal Investigator: Andreas Kempf
Affiliation: Institute for Combustion and Gas Dynamics, Chair of Fluid Dynamics, University of Duisburg-Essen

Simulation of Non-Ideal Effects in Shock-Tubes
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.
Principal Investigator: Andreas Kempf
Affiliation: Institute for Combustion and Gas Dynamics, Chair of Fluid Dynamics, University of Duisburg-Essen

Multi-Scale Study of Reactive Engine Spray
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.
Principal Investigator: Heinz Pitsch
Affiliation: Institute for Combustion Technology, RWTH Aachen University, Germany

Large-Eddy-Simulations of the Unsteady Aerodynamics of Oscillating Airfoils at Moderately High Reynolds Numbers
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 exhibit non-linear aerodynamic responses to small-amplitude pitch oscillations whereas the classical theories predict only a linear response. In the current work we investigate the dynamics of pitching airfoils to understand the flow phenomenon which causes the breakdown of classical models, and also attempt to describe a new simplified model which takes into account the non-linearities observed in the NLF airfoils.
Principal Investigator: Dan S. Henningson
Affiliation: KTH Royal Institute of Technology, Stockholm (Sweden)

Influence of Topography on the Turbulent Inflow of Wind Turbines in Complex Terrain
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.
Principal Investigator: Thorsten Lutz
Affiliation: Institute of Aerodynamics and Gas Dynamics (IAG), University of Stuttgart (Germany)

Accident Scenario in a Nuclear Power Plant
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.
Principal Investigator: Eckart Laurien
Affiliation: Institute of Nuclear Technology and Energy Systems (IKE), University of Stuttgart (Germany)

Simulation of Cavitation Phenomena in Francis Turbines
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.
Principal Investigator: Jonas Wack
Affiliation: Institute of Fluid Mechanics and Hydraulic Machinery, University of Stuttgart (Germany)

HEat (and Mass) Transfer in Turbulent Sprays - HETS
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.
Principal Investigator: Luca Brandt
Affiliation: Department of Mechanics, KTH, Royal Institute of Technology (Sweden)