22-10-2012, 05:16 PM
The Performance of a Subsonic Diffuser Designed for High Speed Turbojet-Propelled Flight
ABSTRACT
An initial-phase subsonic diffuser has been designed for the turbojet flowpath of the hypersonic x43B flight demonstrator
vehicle. The diffuser fit into a proposed mixed-compression supersonic inlet system and featured a cross-sectional shape
transitioning flowpath (high aspect ratio rectangular throat-to-circular engine face) and a centerline offset. This subsonic
diffuser has been fabricated and tested at the W1B internal flow facility at NASA Glenn Research Center. At an operating
throat Mach number of 0.79, baseline Pitot pressure recovery was found to be just under 0.9, and DH distortion intensity was
about 0.4 percent. The diffuser internal flow stagnated, but did not separate on the offset surface of this initial-phase subsonic
diffuser. Small improvements in recovery (+0.4 percent) and DH distortion (-32 percent) were obtained from using vane vortex
generator flow control applied just downstream of the diffuser throat. The optimum vortex generator array patterns produced
inflow boundary layer divergence (local downwash) on the offset surface centerline of the diffuser, and an inflow boundary
layer convergence (local upwash) on the centerline of the opposite surface.