Transition Experiments on Slightly Blunted Cones with Distributed Roughness in Hypersonic Flight

‡Slightly blunted cones with smooth tips and roughened frusta were flown in the NASA Ames hypersonic ballistic range through quiescent air environments. Global surface intensity (temperature) distributions were optically measured and analyzed to determine transition onset and progression over the roughened surface. Real-gas Navier-Stokes calculations of model flowfields, including laminar boundary layer development in these flowfields, were conducted to predict key dimensionless parameters used to correlate transition on such configurations in hypersonic flow. For distributed roughness elements totally immersed within the laminar boundary layer, the critical roughness Reynolds number correlating approach was found to well model transition onset and progression over the roughened conic frusta. The critical value of the roughness Reynolds number for transition was found to be 269  20%, in agreement with the critical value of 250  20% determined in earlier experiments for transition on rough, blunt bodies in hypersonic free flight.