Effect of compressibility and heat transfer on separated turbulent boundary layers*

Wall-resolved large-eddy simulations (WRLES) of the compressible Navier-Stokes equations are conducted of turbulent boundary layers subjected to adverse and then favorable pressure gradients over a flat plate, to explore the impact of compressibility and heat transfer on the dynamics of separated flows. Freestream Mach numbers ranging from 0.2 to 0.9, as well as adiabatic and cool wall boundary conditions are considered, with varying Reynolds numbers. Separation and reattachment is induced via a suction and blowing top boundary condition. A synthetic turbulent inlet is used. Mean velocity, pressure, and temperature contours around the separation bubble are compared. The effects of compressibility on mean velocity profiles are isolated by comparing different transformations. Profiles of Reynolds stresses and thermodynamic fluctuations around the bubble are also explored. Streamwise distributions of skin friction and pressure coefficients, and their fluctuations are examined for each case. The unsteadiness of the separation bubble is evaluated through spectral and modal analyses.