Enthalpy effects on hypervelocity boundary-layer transition: Ground test and flight data

Boundary-layer-transition experiments on a 5-deg half-angle cone at 0-deg angle of attack were performed in the T5 hypervelocity shock tunnel. The test gases investigated included air, nitrogen, and carbon dioxide. Reservoir enthalpies were varied from 3 to 27 MJ/kg and reservoir pressures from 10 to 95 MPa, depending on the gas and tunnel settings. No clear relationship is found to exist between the transition Reynolds number based on the boundary-layer-edge conditions and the reservoir enthalpy. However, when the reference temperature conditions are used instead, the different test gases are distinguishable and ordered according to their dissociation energy. Data from a free-flight experiment are also compared with the shock tunnel experiments. When the transition Reynolds numbers are evaluated at the boundary-layer-edge conditions, they are an order of magnitude higher than the tunnel results. However, when the reference conditions are used, the flight data fall within the same range as the experiments, although the trend with reservoir enthalpy is reversed.