Compressible equilibrium turbulent boundary layers at nonadiabatic wall conditions

Experimental data have been obtained to define test conditions necessary for a compressible, naturally developing, equilibrium turbulent boundary layer. The model consisted of a flat plate that was tested in the NASA Langley Research Center 8-ft high temperature tunnel. For the present study, the nominal boundary-layer edge Mach numbers were 5.0 and 6.2. The local Reynolds number based on boundary-layer edge conditions and plate length ranged from 8 × 106 to 39 × 106. The nominal ratio of adiabatic wall to actual wall temperature was 5.4, due to both the high total temperature of 3300°R and the heat-sink characteristics of the model. This temperature ratio is considerably higher than that obtained in previous compressible boundary-layer studies and simulates hypersonic flight under highly cooled wall conditions, which are anticipated for hypersonic cruise vehicles. The data indicate that a momentum thickness Reynolds number of at least 4000 is required for an equilibrium turbulent boundary layer, which is in approximate agreement with incompressible studies. This criterion was determined by comparing the transformed wake strength of the boundary layer with the incompressible data of Coles. Also, several shape factors were examined and found to support the trend shown by the wake strength.