DNS of supersonic turbulent boundary layers over rough surfaces

Surface roughness effects can significantly alter the mechanical and thermal loads applied on high-speed vehicles. Different superficial treatments can lead to the formation of smooth and rough regions, to which the incoming flow is forced to adjust. In this study, we present direct numerical simulations of smooth and rough zero-pressure-gradient adiabatic turbulent boundary layers at Mach numbers 0.3 and 2, enabling a direct comparison between supersonic and subsonic regimes. The geometry is composed of an initial smooth surface that is followed by a rough wall composed of 3D cubical elements, a structured and well-characterized arrangement. The interaction between compressibility and surface roughness, clearly visible with a pattern of compression and expansion waves, is analyzed considering its implication in turbulence and thermal statistics of the flow. The streamwise adjustment of the turbulent flow to the rough surface is then characterized by assessing the growth of an internal boundary layer (IBL). Preliminary analysis shows profound differences in the outer layer similarity of kinetic and thermal fields with reference smooth cases, as well as the need for more suitable definitions to characterize IBL growth when compressibility effects are present.