Hypersonic Transition Research in the Boeing/AFOSR Mach-6 Quiet Tunnel

Abstract

A Mach-6 Ludwieg tube is being developed for high Reynolds number quiet-flow operation. The modelsupport centerbody had been causing upstream separation when the nozzle-wall boundary layers became laminar at low pressures. The centerbody has now been removed, resulting in attached Mach 5.7 quiet flow below 8 psia total pressure. Pitot measurements show that low-noise flow begins at the same 8 psia, from halfway down the nozzle to near the nozzle exit. Thus, transition in the nozzle-wall boundary layer is apparently bypassing the usual linear instability processes. Measurements of the static pressure on the diffuser walls show large fluctuation when the nozzle-wall boundary layer is laminar, probably due to upstream propagation of bleed-slot jet noise from the diffuser. Finally, initial oil-flow images show the development of crossflow vortices on a sharp cone at angle of attack, and hot-wire measurements show initial evidence of instability waves on a sharp cone at zero angle of attack.