A Review of Experimental Studies of Surface Roughness and Blowing on the Heat Transfer and Skin Friction to Nosetips and Slender Cones in High Mach Numbers Flows
A review is presented of the experimental programs conducted from the late 1970s to the early 1990s at CUBRC to examine the separate and combined effects of surface roughness and blowing on the heating and skin friction to blunt nosetips, capsule heat shields and to slender conical vehicles. These studies were supported by the Air Force with the purpose of providing measurements with which to develop and validate the tools used to describe the shape change of ablating nosetips, transpiration cooling of spherical nosetips, and the effects of roughness and blowing on the performance of maneuvering reentry vehicles. In these studies we employed sand grain and patterned roughness surfaces constructed with grit roughness, and with hemispherical and conical roughness elements respectively. Unique heat transfer and skin friction instrumentation was developed to provide measurements of both the average surface heat transfer and skin friction, and the detailed heating over individual roughness elements. Unique models and instrumentation were also developed to measure heat transfer and skin friction on both smooth and rough surfaces with and in the absence of surface blowing. The measurements made in these studies have been analyzed to provide data sets for code validation, and correlations of roughness-induced heating enhancement in terms of roughness height, shape, spacing, and blowing parameters. An analysis of the measurements made in these studies brings into serious question the use of relationships developed in water tunnel and low velocity airflows to relate the surface characteristics of a rough surface to an equivalent sand-grain rough surface for high-speed flows. We conclude with a discussion of how the measurements and correlations obtained in these studies have been employed to design the models for studies of surface roughness and blowing effects on the aerothermal characteristics of a capsule with a hemispherical nose cap.