Direct numerical simulation of crossflow instability excited by microscale roughness on HIFiRE-5

Direct numerical simulation is performed on a 38.1% scale HIFiRE–5 forebody to study stationary crossflow instability. Computations use the US3D Navier–Stokes solver to simulate Mach 6 flow at Reynolds numbers of 8.1×10 /m and 11.8×10 /m, which are conditions used by quiet tunnel experiments at Purdue University. Distributed roughness with point– to–point height variation on the computational grid and maximum heights of 0.5–4.0 μm is used with the intent to emulate smooth–body transition and excite the naturally–occuring most unstable disturbance wavenumber. Disturbance growth rates and wavelength evolution are analyzed, and the effect of roughness height and forcing character is considered. A steady physical mechanism for the sharp increase in wall heat flux seen in both computations and experiment is introduced. Crossflow vortex coalescence is observed and a possible cause is discussed.