Surface Roughness Effects on the Hypersonic Turbulent Boundary Layer

Citation

Berg, Dale Evan (1977) Surface Roughness Effects on the Hypersonic Turbulent Boundary Layer. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/2S44-JV38. https://resolver.caltech.edu/CaltechETD:etd-11142006-154140

Abstract

NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. An experimental investigation of the response of a hypersonic turbulent boundary layer to a step change in surface roughness has been performed. The boundary layer on a flat nozzle wall of a Mach 6 wind tunnel was subjected to abrupt changes in surface roughness and its adjustment to the new surface conditions was examined. Both mean and fluctuating flow properties were acquired for smooth-to-rough and rough-to-smooth surface configurations. The boundary layer was found to respond gradually and to attain new equilibrium profiles, for both the mean and the fluctuating properties, some 10 to 25 [...] downstream of the step change. Mean flow self-similarity was the first to establish itself, followed by the mass flux fluctuations, followed in turn by the total temperature fluctuations. Use of a modified Van Driest transformation resulted in good correlation of smooth and rough wall data in the form of the incompressible law of the wall. This is true even in the nonequilibrium vicinity of the step for small roughness heights. The present data are found to correlate well with previously published roughness effect data from low and high speed flows when the roughnesses are characterized by an equivalent sand grain roughness height. Existing correlations based on low speed data were found to be unsuccessful in predicting the effect of this roughness on the skin friction and velocity profile. The indiscriminate use of low speed roughness effects correlations to predict the effects of roughness on supersonic and hypersonic flows must therefore be regarded as a procedure subject to gross errors. Significant pressure and temperature history effects were observed throughout the boundary layer. The existence of these effects was found to create a nozzle wall boundary layer whose properties were far different than those in a boundary layer on a flat plate in the freestream, raising questions about the validity of simulating the flat plate boundary layer with the nozzle wall boundary layer.

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