Two-dimensional viscous simulation of inlet/diffuser flows with terminal shocks

Abstract

Two-dimensional Navier-Stokes solutions of the flow through three inlet/diffuser configurations with terminal shock systems are reported. Calculations without bleed indicate that the terminal shock location is very sensitive to the outflow back pressure. For cases where there are little or no available experimental results, it becomes difficult to estimate the back pressure that will result in a terminal shock. Estimates based on quasi-onedimensional analysis are not found adequate for complex two-dimensional flows. It is found that since the flow downstream of the terminal shock is subsonic, and what happens at the outflow boundary affects the flow inside the inlet, enough of the subsonic diffuser must be modeled to accurately predict the terminal shock region. The diffuser portion should be fairly long with the outflow boundary occurring in a region of more or less uniform flow to be able to prescribe a uniform back pressure. The second configuration studied was investigated with and without incorporating bleed in the code. It is found that the use of bleed stabilizes the shock location and allows solutions which, without bleed, result in unstarting of the inlet. The third configuration required a significant amount of bleed through the ramp and cowl surfaces (both ahead and behind the throat) to avoid separation and provide uniform flow at the engine-face station. Comparisons are made with available experimental data. Nomenclature h - throat height M = Mach number P = pressure, N/m2 Re = Reynolds number T = temperature, K x = streamwise location from the inlet face a. = angle of attack Subscripts b = outflow boundary conditions / = inflow boundary conditions 0 = stagnation oo = freestream condition