| Large disturbances and decreased Mach number in the core flow were sometimes found in the downstream end of the nozzle of the Boeing/AFOSR Mach-6 Ludwieg Tube at Purdue University. The cause of the disturbances has been identified using Kulite pressure transducer, hot wire, and hot film measurements of the flow in the tunnel. These disturbances were found to be separations caused by shock/boundary-layer interactions in the diffuser, often originating from shocks generated at the sting support. Some disturbances were found to propagate upstream about 100 boundary layer thicknesses. The large upstream effect is due to the laminar boundary layers being very susceptible to separation. Attempts to prevent the separations from propagating upstream included an improved sting mount, compression rings in the diffuser to thin the boundary layer, and trip rings, in the nozzle and diffuser, to trip the boundary layer. These attempts were not successful in eliminating the separation in the nozzle. A diffuser section with an increased area is proposed to prevent the separations from propagating upstream. |
