| Mixed-compression inlets are needed by turbojet engines powering aircraft intended to cruise at Mach numbers exceeding about 2.5 for efficient conversion of inlet air's dynamic pressure to static pressure. Unfortunately, mixed-compression inlets are not very stable because of flow separation from shock-wave/boundary-layer interactions, which changes the effective inlet surface geometry. In this study, two methods for controlling the effective inlet geometry for stable fluid flow in a mixed-compression inlet are proposed and investigated by using computational fluid dynamics (CFD). CFD simulations were performed to (1) characterize the near-throat flow of the mixed-compression inlet under critical flow conditions with bleed and (2) examine free-stream surfaces formed by two proposed control methods.; In the first set of simulations, critical flow through an axisymmetric, mixed-compression inlet was examined using two different bleed boundary conditions to model the flow through the cowl and centerbody bleed holes. In one bleed boundary condition, the locations of the bleed holes were discerned. In the other, each row of bleed holes was modeled as a porous surface, where the number of bleed holes in each row was accounted for to give the correct bleed rate. These simulations characterized the shock structure in the throat region of the inlet and indicated that the bleed-hole configuration, in addition to the overall bleed rate, is a central element in determining the shock structure and strength in this region. The second set of simulations uses combined supersonic injection and suction in a turbulent, supersonic crossflow to generate a desired free-stream surface that behaves like a wall of the inlet except with a slip surface. Key properties of the jet structure were well-captured and results for the height of the surface generated indicate that there is little impact as the Mach number of the injected fluid is increased. The third set of simulations uses subsonic injection into a recessed cavity placed in a turbulent, supersonic crossflow. The driven fluid is used to control the deflection of the crossflow by the cavity and to modify the boundary layer downstream of the cavity. (Abstract shortened by UMI.)... |
