LDV Measurement Near a Rough Surface for a Turbulent Boundary Layer

LDV(Laser Doppler Velocimeter) measurement has been made close to a rough surface beneath an equilibrium boundary layer. The experiments were conducted at the momentum thickness Reynolds number of 6,000 and the roughness Reynolds number of 150. The local skin friction coefficient can be represented as the sum of the mean flow momentum flux and the Reynolds shear stress at the top surface between the roughness elements. The moment centroid of the drag acting on the rough surface measured from the top of the roughness element might be represented as the integral length scale on both the mean flow momentum flux and Reynolds shear stress estimated in the cavity between the roughness elements. The integral length scales of the mean flow momentum flux and the Reynolds shear stress contribute 30% and 70% respectively to the moment centroid.