Josef Ballmann

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.

A numerical scheme for axisymmetric elastic waves in solids

Abstract The paper considers the axisymmetric stress wave propagation in linear elastic solids which is governed by a system of hyperbolic PDEs with a source term. First, an explicit finite difference scheme is dealt with. Then problems related to the stress wave propagation and focussing in two-dimensional axisymmetric solids are studied using the obtained numerical scheme. Results are presented for the wave propagation in a half space loaded by an impact in a circular surface area, the dynamic stress intensity factor of a penny-shaped crack, the focussing of the von Schmidt wave in an impacted cylinder and the wave focussing in a hemispherically ended cylinder. For reasons of validation, comparisons are made with results gained by other authors. Some new improvements and explanations of the stress increases at cracks and in focussing zones could be attained.

TWO TECHNIQUES FOR THE ABSORPTION OF ELASTIC WAVES USING AN ARTIFICIAL TRANSITION LAYER

Abstract The paper deals with the treatment of artificial boundaries within the framework of characteristic-based finite difference methods for the propagation of elastic waves inlarge or infinite solids. In order to restrict the computational domain mainly to the area of technical interest and to suppress non-physical reflections on its boundary, an absorbing transition layer adjacent to this kernel area is used. The transition layer is designed to match the material properties in the kernel area so that outgoing waves can propagate across the interface between the kernel area and the transition layer without reflection and are almost absorbed in that layer. Two different techniques are adopted for the transition layer. One gradually reduces the amplitude of waves in the transition layer, and the other modifies the wave speeds there. Together with dissipative finite difference schemes, both techniques show numerical efficiency. Numerical examples including cracked media, where plane wave fronts and curved wave fronts (e.g. radiating from the crack tip) occur, are presented.

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

Modeling of Transition Effects in Hypersonic Intake Flows Using a Correlation-Based Intermittency Model

Within the frame of the GRK 1095 (Research Training Group) ”Aero-thermodynamic Design of a Scramjet Engine for Future Space Transportation Systems” a numerical and experimental analysis of a scramjet intake has been initiated at RWTH Aachen University. The paper presents an overview of the ongoing work on the numerical simulations using a well validated Reynolds averaged Navier Stokes solver, namely QUADFLOW. For the simulations the γ-Reθ model proposed by Langtry/Menter 1, 2 extended with in-house correlations for onset and length of transition is applied. For validation purpose, several simulations of subsonic flat plate flows and hypersonic double ramp configurations have been performed. The validation with respect to scramjet intakes is done by comparing the numerical results of this paper to experimental results of DLR Cologne.

Effect of Flap and Slat Riggings on 2-D High-Lift Aerodynamics

In this paper an extensive parametric study concerning the effect of flap and slat riggings on the 2-D high-lift flow past a three-element airfoil system is presented. The numerical approach for solving the Reynolds-averaged Navier-Stokes equations uses an implicit finite volume scheme of second order accuracy in space on a patched multizonal grid. The Spalart-Allmaras one-equation turbulence model is employed. Six design parameters have been investigated comprising the deviation, gap, and overhang of the slat and of the flap whose settings are centered about the values in practice for takeoff. Good agreement with experiments is obtained for prestall angles of attack. Computations show that both C l and C l /C d have an optimum with every design parameter. The trends in the high-lift flow observed are in accordance with both experiments and computations reported in the literature. C l and C l /C d are found to be more sensitive to deviations and gaps than to overhangs.

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.

Development of a Modular Method for Computational Aero-structural Analysis of Aircraft

This paper outlines the development of the aero-structural dynamics method SOFIA over the duration of the Collaborative Research Center SFB 401. The algorithms SOFIA applies for the spatial and the temporal aero-structural dynamics coupling are presented. It is described in particular how SOFIA’s load and deformation transfer algorithms suitable for non-matching grids at the coupling interface were enhanced towards the application to complete aircraft configurations. The application of SOFIA to various subsonic and transonic aeroelastic test cases is discussed.

Numerical Investigation of Hypersonic Intake Flows

A numerical and experimental analysis of scramjet intake flows has been initiated at RWTH Aachen University as part of the Research Training Group GRK 1095: “Aero-Thermodynamic Design of a Scramjet Engine for a Future Space Transportation System”. This report presents an overview of the ongoing work on the numerical simulations of air intake flow using two different, well validated Reynolds averaged Navier Stokes solvers. Several geometry concepts e.g. 2D intake, 3D intake using a single or double ramp configuration were investigated. One example for the so-called 2D intake can be seen in Fig. 1 and for a 3D intake in Fig. 2. To analyze the effects these different geometries have on the flow, especially on the separation bubble in the isolator inlet as well as on transition and efficiency, several numerical simulations (2D and 3D) were performed using a variety of turbulence models. Mostly the Spalart–Allmaras – one equation model and the so called SSG–Reynolds stress model by Speziale, Sakar and Gatski were used. The data obtained will be compared with experimental results. These experiments started in March 2007. It has to be said that not all results presented here were achieved using the NEC computing cluster. For comparison several calculations were conducted on the IBM Jump system of the Julich Research Centre and on the SUN cluster of RWTH Aachen University. At the end of this report we give comments on the computational performance.

Dynamic aero-structural response of an elastic wing model

Abstract A highly elastic rectangular wing model with a supercritical airfoil was designed and manufactured to study aero-structural equilibrium configurations and aerodynamic damping at various speeds in a subsonic wind tunnel. The supporting structure is a cross-shaped spar. A foam with negligible stiffness is used to provide the aerodynamic surface of the wing. Experimental data are used to examine a coupled algorithm for simulating fluid–structure interaction which simultaneously solves the Euler or Navier–Stokes equations and the structural dynamics equations in the time domain. The elastic wing is modelled by a generalized Timoshenko-type beam with six degrees of freedom for a material cross-section. Correct reproduction of the aero-structural equilibrium shape of the wing model and the deflection under zero lift and nonzero lift conditions, time consistency of unsteady deformations and pressure fluctuations are examined by comparing numerical and experimental results.