Roughness Considerations for HIFiRE-1 Vehicle

Abstract

*The Hypersonic International Flight Research Experimentation (HIFiRE) program is a hypersonic flight test program executed by the Air Force Research Laboratories (AFRL) and Australian Defence Science and Technology Organization (DSTO). The test geometry consists of a 7-degree half angle cone with 2.5 mm bluntness followed by a cylinder and flare. The experiment test window is between Mach 7.2 and 7.4. The emphasis of flight one is aerothermodynamics, and boundary layer transition is the primary experiment. This makes it critical to specify allowable roughnesses and trips. No theory is available for estimating allowable roughness heights, so correlations must be used. This paper describes several correlations for distributed nose tip roughness and discrete frustum roughness. Generally, the correlations all give reasonable results about the same order of magnitude, but show considerable spread. Correlations based on integral parameters require fairly realistic walltemperature distributions in order to get integral values correct. When making roughness estimates, several correlations should be examined, and decisions on trips and roughness must be made using judgment based on how near one is to a specific criterion. Assessment of roughness effects is essentially an exercise in uncertainty management and risk mitigation.