Experimental investigation of hypersonic buzz on a high cross-range shuttle configuration.

An experimental study confirming the existence of hypersonic buzz in the separated region of a space shuttle's downward deflected control surface is described. Wind tunnel tests in helium on a 1:100 scale model of a shuttle type configuration at M = 17.5 clearly demonstrated the occurrence of large scale pressure oscillations throughout a substantial range of angles of attack and control surface deflections. Measurements of surface pressure fluctuations along with high speed schlieren photography served to delineate the boundaries of the phenomenon and to identify the physical parameters necessary for the onset of a buzz condition. Prominent spectral energy peaks were also observed in the surface pressures that could be directly correlated with the instability. These conditions were found to be strongly dependent on the presence of multiple shock interactions and the position of these interactions relative to the location of a reattaching shear layer.