Birgit Reinartz

Aerodynamic Performance Analysis of a Hypersonic Inlet Isolator Using Computation and Experiment

A two-dimensional mixed compression inlet model with a subsequent isolator section is tested under Mach 4 and 5 flight conditions. Different configurations of the isolator are assessed with respect to their compression efficiency. The experimental investigations yield schlieren pictures of the isolator flow and static surface pressure measurements. The numerical simulations are performed with a Reynolds-averaged Navier-Stokes solver using a k-w turbulence model, especially extended for modeling high-speed wall-bounded flows and separation regions. The close collaboration of experiment and simulation is beneficial: Validation of the simulation is achieved by the test data and the flowfield information available in the computational fluid dynamics results is employed to interpret the experimental findings and to compute the performance parameters. The computed static pressure ratios are in excellent agreement with empirical predictions. Furthermore, the investigations show that increasing the isolator length reduces the pressure sensitivity of the inlet. However, the experimental tests show that above a certain isolator length, no further increase of the sustainable backpressure is possible.

Numerical Investigation of Wall Temperature and Entropy Layer Effects on Double Wedge Shock / Boundary Layer Interactions

A combined experimental as well as computational analysis of hypersonic flows over heated ramp and wedge configurations has been initiated. This paper presents an overview of the ongoing work on the numerical simulation using two different, well validated Reynolds averaged Navier–Stokes solvers with a variety of turbulence models. Different surface temperatures are specified to investigate the impact on the shock / boundary layer interaction and on the size of the separation. To analyze the effect of an entropy layer behind a blunt leading edge on the structure of the boundary layer as well as on the development of the inviscid flow field, flows over double wedge configurations with different nose radii are computed and compared to the experimental results

COMPUTATION OF WALL HEAT FLUXES IN HYPERSONIC INLET FLOWS

Within the frame of the German Collaborative Research Center SFB 253 “Fundamentals of Design of Aerospace Planes”, generic supersonic and hypersonic engine inlet configurations are investigated both numerically and experimentally. This paper presents an overview of the ongoing work on the numerical simulation of high-speed inlet flows solving the complete Reynolds averaged Navier-Stokes equation with a block-structured, cell-centered finite-volume method. The turbulence model is Wilcox’s low Reynolds number k − ω model with some extensions for modeling high-speed wall-bounded flows and separation regions. The first configuration involves a supersonic inlet with interior compression and the development of a subsequent shock train. This test case is mainly used to demonstrate the present state of a newly implemented advanced multigrid method for supersonic turbulent flows. Of recent interest is the accurate prediction of wall heat transfer rates in the second test configuration. This configuration is a heated compression ramp model which is presently investigated experimentally in a shock tube to assess the influence of the wall temperature on boundary layer separation behavior.

Effects of Sidewall Compression and Relaminarization in a Scramjet Inlet

This paper presents the numerical simulations and the performance analysis of a scramjet inlet as part of a combined experimental and numerical study. A well-validated finite volume flow solver was used to simulate a scramjet inlet with a double ramp configuration for outer compression, including varying degrees of sidewall compression. The computed wall pressure and heat transfer in the symmetry plane are in close agreement with the measurements, and the numerical results indicate that the weak sidewall compression alters the inlet performance significantly. The effects of partial relaminarization over the expansion corner, before the interior part of the inlet, is isolated and investigated in both the experiment and simulation. It is shown that relaminarization of a boundary layer is predicted accurately using the current numerical methods. This work represents a contribution to the understanding of the effects of sidewall compression and relaminarization in designing a scramjet inlet.

Numerical Investigation of Compressible Turbulent Boundary Layer Over Expansion Corner

This paper presents an ongoing project on numerical investigation of the rapid distortion and the subsequent relaxation of compressible turbulent boundary layers over expansion corners. A well-validated finite volume flow solver comprising several turbulence models was used to simulate two test cases of supersonic flows encountering abrupt expansions in the mean streamwise direction. When comparing with experiments, it is concluded that commonly used turbulence models are capable of predicting the mean flow quantities and the streamwise normal Reynolds stress downstream of the expansion corner with sufficient accuracies. Numerical analysis found that bulk dilatation (change of mean density) and isovolumetric deformation of normal strain rates are mainly responsible for the turbulence reduction across the expansion fan.

Numerical Investigations of the Effects of Sidewall Compression and Relaminarization in 3D Scramjet Inlet

This paper presents the numerical simulations and performance analysis of a 3D scramjet inlet with focus on the effects of sidewall compression and relaminarization. A well-validated �finite volume flow solver was used to simulate a scramjet inlet with a double ramp configuration for outer compression and varying degrees of sidewall compression. The computed wall pressure and heat transfer in the symmetry plane are in close agreement with the measurements and numerical results indicate that sidewall compression alters the inlet performance significantly. The effects of relaminarization over the expansion corner prior to the interior part of the inlet is isolated and studied in both experiment and simulation.

Investigation of a Compression Corner at Hypersonic Conditions using a Reynolds Stress Model

An experimental campaign over a compression corner in a Mach 6 hypersonic flow was conducted to investigate the performance of a differential Reynolds stress model (RSM). Two compression angles have been chosen in order to obtain an attached flow (15-degrees) and a separated flow (40-degrees). The numerical results obtained using the RSM were compared with the numerical findings and with the results from standard linear eddy viscosity models and an explicit algebraic Reynolds stress model. As expected, all models performed similarly for the 15-degrees case in terms of wall pressure and heat flux while appreciable differences were visible at 40-degrees when the boundary layer separates. In this case the Reynlds stress based models proved to be superior to the eddy viscosity ones.

Transition Prediction for Scramjets Using γ-Reθt Model Coupled to Two Turbulence Models

Because of viscous interaction in hypersonic flows, the state of the boundary layer significantly influences possible shock-wave boundary-layer interaction as well as surface heat loads. Hence, for engineering applications, the efficient numerical prediction of the laminar-to-turbulent transition is a challenging and important task. Within the framework of the Reynolds-averaged Navier–Stokes equations, Langtry–Menter proposed the γ-Reθt transition model using two transport equations for the intermittency and Reθt combined with the shear stress transport turbulence model. The transition model contains two empirical correlations for the onset and length of transition. Langtry–Menter designed and validated the correlations for the subsonic and transonic flow regimes. For applications in the hypersonic flow regime, the development of a new set of correlations proved necessary. Within this paper, we propose a next step and couple the transition model with the Speziale–Sarkar–Gatski/Launder–Reece–Rodi ω Reynold...

Investigation of Hypersonic Intakes Using Reynolds Stress Modeling and Wavelet-Based Adaptation

The simulation of hypersonic flows is computationally demanding due to the large gradients of the flow variables at hand, caused both by strong shock waves and thick boundary or shear layers. The resolution of those gradients imposes the use of extremely small cells in the respective regions. Taking turbulence into account intensifies the variation in scales even more. Furthermore, hypersonic flows have been shown to be extremely grid sensitive. For the simulation of fully three-dimensional configurations of engineering applications, this results in a huge amount of cells and, as a consequence, prohibitive computational time. Therefore, modern adaptive techniques can provide a gain with respect to both computational costs and accuracy, allowing the generation of locally highly resolved flow regions where they are needed and retaining an otherwise smooth distribution. In this paper, an h-adaptive technique based on wavelets is employed for the solution of hypersonic flows. The compressible Reynolds-average...The simulation of hypersonic flows is computationally demanding due to the large gradients of the flow variables at hand, caused both by strong shock waves and thick boundary or shear layers. The resolution of those gradients imposes the use of extremely small cells in the respective regions. Taking turbulence into account intensifies the variation in scales even more. Furthermore, hypersonic flows have been shown to be extremely grid sensitive. For the simulation of fully three-dimensional configurations of engineering applications, this results in a huge amount of cells and as a consequence prohibitive computational time. Therefore, modern adaptive techniques can provide a gain with respect to both computational costs and accuracy, allowing the generation of locally highly resolved flow regions where they are needed and retaining an otherwise smooth distribution. In this paper, an h-adaptive technique based on wavelets is employed for the solution of hypersonic flows. The compressible Reynolds averaged Navier-Stokes equations are solved using a differential Reynolds stress turbulence model, well suited to predict shock-wave-boundary-layer interactions in high enthalpy flows. Two test cases are considered: a compression corner at 15 degrees and a scramjet intake. The compression corner is a classical test case in hypersonic flow investigations because it poses a shock-wave-turbulent-boundary-layer interaction problem. The adaptive procedure is applied to a two-dimensional configuration as validation. The scramjet intake is firstly computed in two dimensions. Subsequently a three-dimensional geometry is considered. Both test cases are validated with experimental data and compared to non-adaptive computations. The results show that the use of an adaptive technique for hypersonic turbulent flows at high enthalpy conditions can strongly improve the performance in terms of memory and CPU time while at the same time maintaining the required accuracy of the results.

Numerical Simulation of Hypersonic Air Intake Flow in Scramjet Propulsion Using a Mesh-Adaptive Approach

The intake of a supersonic combustion Ramjet (Scramjet) mostly consists of one or more external compression ramps followed by an internal part. Oblique shock waves generated by the ramps, the cowl and the side walls are performing the compression of the incoming flow. Multiple interesting and complex physical phenomena may occur, such as shock-boundary layer interaction, laminar-turbulent transition, compressible relaminarization, flow separation, etc.