Free-flight experiments in high-speed wind tunnels

Abstract

Free-flight experiments are an invaluable tool in hypersonic wind tunnels for studying a range of unsteady high-speed-flow problems: relevant examples include store, stage, and shroud separation, destructive re-entry and meteoroid fragmentation. Also, since traditional force-balance methods are difficult or impossible to implement in short-duration hypersonic tunnels, free-flight techniques can provide a convenient means of aerodynamic measurement in such facilities, provided the model motion can be accurately recorded. In the first part of this seminar, I will describe the development of a class of optical-tracking techniques for the nonintrusive measurements of model orientation and position in free-flight experiments. The common thread of these tracking techniques is the combination of subpixel edge detection applied to experimental images (typically shadowgraph or schlieren) with least-squares fitting of a generated model outline. The most sophisticated of these techniques has been shown to be capable of 5 DoF measurements of arbitrary geometries (with a single camera), with a precision approaching 1 micron and 0.001 degrees. In the second part of the seminar, I will describe the application of free-flight and optical-tracking techniques to several high-speed problems of interest, including the determination of force and moment coefficients on complex bodies, separation of objects from a ramp surface, and aerodynamic breakup of particle clusters.