PIV Experiments on a Rough Wall Hypersonic Turbulent Boundary Layer

Abstract

In the aerodynamics design of hypersonic vehicles, it is necessary to understand the behavior of turbulence with complex boundary conditions. Surface roughness is one such boundary condition that signi cantly a ects turbulent hypersonic boundary layers. Experiments using Particle Image Velocimetry were performed to study the e ects of surface roughness on a hypersonic (Me = 7:3), low Reynolds number (typically Re = 5500), turbulent boundary layer. Two di erent types of roughness elements on a at plate model were used: diamond mesh and d-type square bars. Two di erent heights of roughness elements ranging from partially rough (about 38 viscous units) to fully rough (about 136 viscous units) regime with varying roughness density were tested. The van Driest transformed mean velocity pro les for rough walls showed the expected response to roughness, which is the shift of the velocity pro le below the standard log-law, without any change in shape. In the region closer to the wall, the streamwise uctuation was in uenced by the size of the diamond mesh roughness. However, the uctuations were in uenced throughout the boundary layer in case of square bar elements. The wall-normal uctuations indicated no apparent dependence on the size of roughness in case of mesh elements. Some dependence was observed in case of square bars elements. The size and shape of the roughness elements signi cantly altered the Reynolds shear stress. Also, signi cant compressibility e ects were demonstrated by the roughness elements at this high Mach number.