DNS of a spatially evolving transitional/turbulent boundary layer at M=2.0

Spatial direct numerical simulations (DNS) are used to study the formation and development of three-dimensional vortical structures in a supersonic flat plate boundary layer, where the freestream Mach number is 2.0. Three-dimensional random disturbances are superimposed on the laminar profile for Reynolds numbers based on the displacement thickness of 1300 and 2000 at the inlet plane of the boundary layer computational box. The high intensity disturbances induce hairpin vortices and the low speed streak watersheds downstream. Numerical results show the evolution of hairpin vortices on the streak watersheds into a large-scale structure due to the streak breakdown, and secondary and tertiary hairpin vortex structures are generated. A comparison of the fully turbulent isothermal wall boundary layer up to Reθ =1660based on the momentum thickness and the turbulent adiabatic wall boundary layer indicates that the wall thermal condition affects the turbulent structures and the RMS velocity profile. The finer streaks and a more population of the streak watershed of the isothermal wall boundary layer explain these differences.