Effect of Mach Number on Flow Past Microramps

Abstract

Micro vortex generators have the ability to alter the near-wall structure of compressible turbulent boundary layers to provide increased mixing of high-speed fluid, such that the boundary layer remains healthy even with some disturbance imparted to the flow. Because of their small size, micro vortex generators are embedded in the boundary layer and may provide reduced drag when compared with traditional vortex generators. To examine their potential, a detailed computational study was undertaken of microramps with a height of h similar to 0.5 delta in a supersonic boundary layer at M = 1.4, 2.2, and 3.0. The large eddy simulation results indicate that microramps have a greater impact at lower Mach number near the device, but this influence decays faster than at the higher Mach numbers. This may be due to the additional dissipation caused by the primary vortices with smaller effective diameter at the lower Mach number, such that their coherency is easily lost, causing the streamwise vorticity and the turbulent kinetic energy to decay quickly. The normal distance between the vortex core and the wall had similar growth, indicating weak correlation with the Mach number; however, the spanwise distance between the two counter-rotating cores further increases with lower Mach number.