Planar diffuser performance improvement using injection along the straight diverging walls at subsonic to transonic Mach numbers

Abstract

Planar diffusers with injection along the diverging walls were investigated relative to their pressure recovery performance. Injection orientation, location and slot width were varied for diffusers with aspect ratios of one and six and an area ratio of 11.4. Two inlet flow blockage conditions, 0.04 and 0.20, were investigated. Inlet Mach numbers varied from 0.3 to 0.9 and injector Mach numbers varied from 0.3 to 0.9, with the 30° diffuser exiting to the atmosphere. Traverses of the exit and inlet planes using a pitot tube were made using a computerized data acquisition, control, and positioning system. Uncertainties of 5% or less were maintained for all tests. The diffuser performance, as measured using a modified pressure recovery relationship, was enhanced exceeding 150% for some diffuser/injector configurations. The best performance was achieved for the configuration with injectors located near the diffuser inlet (throat), using a large injection slot. The optimum orientation for the slot was generally parallel to the diffuser inlet, although the orientation parallel to the walls also worked well. The mass flowrate passing through the diffuser was also increased 20% to in excess of 75% at the same pressure recovery.