A critical evaluation of numerical algorithms and flow physics in complex supersonic flows.

摘要

In this research, two different complex supersonic flows are selected to apply CFD to Navier-Stokes simulations. First test case is "Supersonic Flow over an Open Rectangular Cavity". Open cavity flow fields are remarkably complicated with internal and external regions that are coupled via self-sustained shear layer oscillations. Supersonic flow past a cavity has numerous applications in store carriage and release. Internal carriage of stores, which can be modeled using a cavity configuration, is used for supersonic aircraft in order to reduce radar cross section, aerodynamic drag and aerodynamic heating. Supersonic, turbulent, three-dimensional unsteady flow past an open rectangular cavity is simulated, to understand the physics and three-dimensional nature of the cavity flow oscillations. Influences of numerical parameters such as numerical flux scheme, computation time and flux limiter on the computed flow are determined. Two dimensional simulations are also performed for comparison purposes.; The next test case is "The Computational Design of Boeing/AFOSR Mach 6 Wind Tunnel". Due to huge differences between geometrical scales, this problem is both challenging and computationally intensive. It is believed that most of the experimental data obtained from conventional ground testing facilities are not reliable due to high levels of noise associated with the acoustic fluctuations from the turbulent boundary layers on the wind tunnel walls. Therefore, it is very important to have quiet testing facilities for hypersonic flow research. The Boeing/AFOSR Mach 6 Wind tunnel in Purdue University has been designed as a quiet tunnel for which the noise level is an order of magnitude lower than that in conventional wind tunnels. However, quiet flow is achieved in the Purdue Mach 6 tunnel for only low Reynolds numbers. Early transition of the nozzle wall boundary layer has been identified as the cause of the test section noise. Separation bubbles on the bleed lip and associated fluctuations induced near the bleed lip were identified as the most likely cause of early transition. The existence of steady and/or unsteady separation bubbles on the main flow and the bleed flow side of the nozzle lip is investigated and a new geometry is designed to eliminate the separation bubbles.; Keywords: cavity, transition, quiet tunnel, supersonic flow, hypersonic, CFD.