Rough Wall Reentry Heating Analysis. Effect of Surface Roughness Character on Turbulent Boundary Layer Heating

摘要

A Reynolds stress model is used to evaluate the effect of surface roughness on turbulent boundary layers. Roughness is represented by distributed source or sink terms in the various governing equations, the most important term being a sink term in the mean momentum equation describing firm drag on the roughness elements. The blockage effect of closely spaced elements is treated by accounting for the volume fraction occupied by the solid material. Calculations based on the theory have been compared with the available data on the influence of roughness character, where the roughness shape and spacing were varied. Reasonable agreement was obtained against most of Schlichting's low speed data with spherical, spherical segment, and conical roughness elements at various spacings. The cone measurements imply a somewhat higher effective drag coefficient than observed on the other shapes. The second set of experiments that were analyzed in detail were performed by Acurex under supersonic conditions, with a number of roughnesses created by grit or chemical etching processes. The heat transfer data and the present theory indicate spacing to be more important than height under the conditions tested.