3D DSMC Simulation of Rarefied Hypersonic Flow over a Sharp Flat Plate

The flow over a sharp flat plate with a finite leading edge angle located in a rarefied hypersonic flow has been investigated numerically with the direct simulation Monte Carlo (DSMC) method using the Dynamic Molecular Collision (DMC) Model based on Molecular Dynamics (MD) simulation of nitrogen molecules. The results of the two-dimensional numerical simulations of the zero leading edge angle plate agree fairly well with the experimental results [Lengrand, J.C. et al. (1992)] in the middle cross section of the span direction. Thus to investigate much more precisely about the detailed physical phenomena in the rarefied hypersonic flow over the sharp flat plate, the three-dimensional numerical simulations have been made. At first, to compare with two-dimensional simulation, the effect of the existence of the finite leading edge angle "the leading edge effect", and the effect of the three-dimensional flow structure due to the side edge of the plate "the finite span effect" are investigated. From these numerical simulations, the flow field around the plate is shown three-dimensionally, and the effects are evaluated to determine the three-dimensional flow structure over the plate. INTRODUCTION Many researchers have investigated the rarefied hypersonic flows around space vehicles with respect to the nonequilibrium characteristics. The external flow field and the boundary layer growth around a body of given shape have the mutual interaction called viscous interaction. This viscous interaction affects the flight characteristics of the vehicles. Thus it is important to analyse this phenomenon. In rarefied regime, the shock wave and the boundary layer "merge" near a leading edge, and in that region, it becomes difficult to distinguish the shock wave from the boundary layer. This region is called the merged layer. A strong nonequilibrium between translational and internal degrees of freedom of molecules could be observed in this region. However the nonequilibrium in the merged layer has not been discussed in detail. In numerical simulations, the direct simulation Monte Carlo (DSMC) method [1] is widely used to simulate the rarefied gas flows. The gas-gas interaction model has very important role in this method. To investigate nonequilibrium between the translational and the internal energy of diatomic molecules, the relaxation of the internal degrees of freedom should be simulated in detail. Thus the molecular collisions, which is micro-scale phenomena, and the macro-scale phenomena of the flow field around a body of given shape, should be treated at one time, because micro-scale phenomena affect macro-scale phenomena and vice versa. The analysis should be done over multi scales, micro to macro. Thus the Dynamic Molecular Collision (DMC) model [2] is chosen as the collision model. The DMC model is derived from a lot of Molecular Dynamics (MD) simulations of diatomic molecule (N2) two-body collisions. It is the statistical model based on micro-scale phenomena for the macro-scale analysing method. The schematic diagram of their relations is shown in Fig.l. To make the analysis easier, a sharp flat plate is chosen as an object. The another reason of deciding an object is that there exists the experimental result [3]. To investigate the merged layer in detail, the numerical simulation is made and compared with the experimental result. There are two elements that could affect the three-dimensional flow structure around the object the finite leading edge angle and the existence of the side edge of the plate. Thus three-dimensional and two-dimensional numerical simulations have made and compared to investigate these effects the leading edge effect and the finite span effect. CP585, Rarefied Gas Dynamics: 22 International Symposium, edited by T. J. Bartel and M. A. Gallis © 2001 American Institute of Physics 0-7354-0025-3/01/$18.00 764