Markus Kindler

Numerical Investigation of the HyShot Supersonic Combustion Configuration

A multivariate assumed PDF approach together with finite-rate chemistry is used for the simulation of the HyShot supersonic combustion configuration. Because the combustor entrance conditions of scramjets at low flight Mach numbers (Ma 8) are close to the ignition limit of hydrogen air mixtures, detailed kinetic schemes are required and an accurate simulation of temperature and temperature fluctuations is essential. In the present paper, experiments of the HyShot supersonic combustion configuration performed at the High

Numerical Simulation of the Internal and External Flowfields of a Scramjet Fuel Strut Injector Including Conjugate Heat Transfer

The use of fuel strut injectors is a promising concept to achieve good mixing and combustion performances in supersonic combustors. In the present paper a lobed strut injector is investigated. The chosen geometry creates streamwise vorticity to enhance the mixing of fuel and air compared to a planar strut. The injector is located in the center of the hot supersonic flow field at the entrance of the combustor. To avoid burning, the strut has to be cooled which is done by the injected fuel. Especially at high flow Mach numbers, the thermal load for the strut may be severe. In the present paper, the strut surface heat fluxes and the temperature distribution in the strut are calculated. Conjugate heat transfer to the strut surface is considered both, from the simulated external air flow to the strut and from the strut to the cold internal hydrogen flow. An all-Mach number preconditioning is used in the numerical code to compute supersonic as well as subsonic flows. The strut investigated is assumed to be out of copper. The coupled simulations provide a survey of the internal strut temperature distribution and delivers accurate boundary and injection conditions (for hydrogen) in cases, where the interior fuel flow and heat transfer are neglected.

Numerical Investigations of Model Scramjet Combustors

In the present paper different types of scramjet (supersonic combustion ramjet) combustors are investigated. Thereby the main difference between the combustors is the way of injecting the fuel into the combustion chamber. The first investigated concept of fuel injection is the injection by strut injectors. Here the injection of fuel is realized by a lobed strut that is located in the middle of the combustion chamber. The second concept for fuel supply is the wall injection of hydrogen. Here the fuel is injected by several holes in the wall of the combustor. Both concepts of fuel injection have different advantages and disadvantages which are explained in detail. Although different performance parameters for both scramjet combustors are introduced this paper will not compare the different techniques among each other. Because of the high Reynolds numbers in scramjet combustors, the need to resolve the boundary layers and the necessity of detailed chemistry, the simulation of scramjets is extremely CPU time demanding.

Delayed Detached Eddy Simulations of Compressible Turbulent Mixing Layer and Detailed Performance Analysis of Scientific In-House Code TASCOM3D

In the present paper a compressible turbulent mixing layer is investigated using Delayed Detached Eddy Simulation (DDES). Thereby two compressible flows are divided by a splitter plate which join downstream of the plate and form a mixing and shear layer. The simulations are performed with the scientific code TASCOM3D (Turbulent All Speed Combustion Multigrid Solver) using a fifth-order upwind biased scheme combined with an improved multi-dimensional limiting process (MLP) (Gerlinger, 2011) for spatial discretization. The inviscid fluxes are calculated using the AUSM+-up flux vector splitting. DDES is a hybrid RANS/LES approach which uses a traditional Reynolds averaged Navier-Stokes (RANS) approach for wall-bounded regions and a Large Eddy Simulation (LES) approach for the mixing section. The simulations show a quasi two-dimensional flow field right after the splitter plate and a following conversion to a turbulent and highly unsteady flow field after short distance. Furthermore the performance of TASCOM3D on different HPC systems is analyzed: a vector (NEC SX-9) and a scalar processor based (Cray XE6) system, both installed at the High Performance Computing Center Stuttgart (HLRS). The investigation points out the challenges and problems in HPC and may serve other researchers as comparison and assistance to achieve good performance on the different architectures.

Assumed PDF Modeling of Turbulence Chemistry Interaction in Scramjet Combustors

A multivariate assumed PDF approach together with finite-rate chemistry is used for the simulation of scramjet combustors. Because the combustor entrance conditions of scramjets at low flight Mach numbers (Ma ≈ 8) are close to the ignition limit of hydrogen air mixtures, detailed kinetic schemes are required and an accurate simulation of temperature and temperature fluctuations is essential. In the present paper, a lobed strut injector concept is used for hydrogen injection which enhances the mixing process by production of streamwise vorticity. The influence of the chosen combustor geometry on the mixing behaviour is investigated in this paper. Moreover a Mach 2 supersonic combustion experiment is simulated to investigate the influence of the chosen reaction mechanism and of the assumed PDF model. A detached flame is obtained and the predicted ignition length is a measure for the accuracy of the used kinetic scheme and the modeling of turbulence chemistry interaction.

Investigation of Hybrid RANS/LES Approaches for Compressible High Speed Flows

In the present paper two different hybrid RANS/LES approaches are investigated to predict compressible high speed flows the DDES (Delayed Detached Eddy Simulation) and the SAS approach (Scale Adaptive Simulation). All simulations are performed with the scientific code TASCOM3D (Turbulent All Speed Combustion Multigrid Solver). For the reconstruction of the interface values of the finite-volume scheme, a fourth/fifth-order upwind biased scheme combined with an improved multi-dimensional limiting process (MLP) is employed. The inviscid fluxes are calculated using the AUSM−up flux vector splitting. In order to prove the capability of the solver to perform LES, a fully developed turbulent channel flow is simulated and compared with experimental data and results obtained by Direct Numerical Simulation (DNS). Thereby discretization schemes of different accuracies and effects of a shock detection sensor are investigated. To compare the capabilities and limits of DDES and SAS in compressible high speed flows a supersonic turbulent mixing layer is investigated. The variation of modeling parameters, grid spacing, and domain widths in spanwise direction are used to asses the different turbulence modeling techniques.

Numerical Investigations of NOX-Formation in Scramjet Combustors

In the present paper the impact of NO X -emissions of aircrafts on ozone is highlighted. The chemical processes of NO X in the troposphere and stratosphere are explained briefly and the formation of NO X under the specific conditions of a scramjet combustor is discussed. Finally a model scramjet combustor with hydrogen injection is investigated numerically using the scientific in-house code TASCOM3D. The results of the simulations demonstrate the formation of NO X in scramjet combustors and are discussed in detail. With regard to the development of NO X reduction strategies further investigations are performed in terms of the variation of the inlet temperature. Variations of other relevant parameters concerning NO X -formation like the equivalence ratio, Mach number at combustor entrance, types of fuel injection, etc. are part of ongoing investigations but will not be discussed in this paper. Finally the performance of the scientific code TASCOM3D on the NEC SX-8 is analyzed.

Delayed Detached Eddy Simulation of a Rotationally Symmetric Supersonic Jet

A Delayed Detached Eddy Simulation (DDES) of a rotationally symmetric free jet is performed with the scientific in-house code TASCOM3D (Turbulent All Speed Combustion Multigrid 3D). The DDES is a hybrid RANS/LES method that employs the RANS approach in the near-wall region and LES modeling otherwise. The transition is achieved by filtering depending on the grid spacing. To preserve the RANS mode in the boundary layer an appropriate blending function is used. The investigated experiment is a supersonic Ma 1.8 jet exiting a nozzle into ambient conditions. The simulation results for the axial velocity, temperature, density and density fluctuations are compared to measured values. Several simulations have been performed to analyze the effect of the modeling constant C DES , grid refinement, and the addition of artificial fluctuations in the boundary layer that are not created inherently in the used approach. The overall agreement between experiment and simulation is quite satisfying although the transition is apparently predicted too far upstream in all simulations.

Numerical Investigations of NOx-Formation in Scramjet Combustors using Wall and Strut Injectors

In the development of new propulsion systems, the ecological impact always has to be considered. On the long run this will also be the case for scramjets, if used for passenger transportation. In the present paper the NOx-formation of scramjet combustors is investigated. The impact of NOx-emissions of aircrafts on the ozone layer is highlighted and the chemical processes of NOx in the troposphere and stratosphere are explained briefly. A short survey of the formation of NOx under the specific conditions of a scramjet combustor is given. In order to analyse the NOx-emissions of a scramjet engine a model scramjet combustor with hydrogen injection is investigated numerically. Thereby the fuel is injected by a lobed strut, or by a wall injector. For the sake of comparability the geometry and boundary conditions are chosen identical. This allows an assessment of the different injection strategies. In a detailed study variation of the flight Mach number, equivalence ratio, of the air inlet contraction ratio and inlet losses is performed. Thus for a model scramjet combustor the influence of different operating conditions on pollutant formation is investigated.