Hypersonic transition induced by three isolated roughness elements on a flat plate

Hypersonic boundary layer transition from laminar to turbulent induced by three isolated roughness elements (ramp, diamond, and cylinder) was investigated by direct numerical simulations based on finite volume formulation with high order MDCD scheme. The effects of roughness shape on the transition mechanism, aerodynamic and aero-thermodynamic performances were quantitatively compared. The transition is dominated by three-dimensional shear layer instability and the streamwise transition locations are almost the same for all three roughness elements. The width of turbulent wake, the drag increment and the heat flux are the largest for cylinder. At the same time, the turbulent wake is the narrowest and drag and heat flux are the lowest for the ramp.