Acoustic field of a shielded rectangular supersonic jet

Abstract

The impact of a flat surface installed parallel to a supersonic rectangular jet of AR = 2 on the far field noise is studied. Far-field cold jet results at design, over-expanded and under-expanded conditions are compared between the free-field jet, the nozzle with the surface matching with the exit lip (h = 0De), and the surface at different stand-off positions away from the jet axis, h = 1, 2, 3 De. Results are shown for all jet azimuthal angles. When the surface is installed at h = 0De, broadband shock-associated noise intensity was decreased and its peak frequency shifted. At NPR = 2.5, shock noise appears to be entirely mitigated. Also, a low frequency noise component is observe below St = 0.15, and assumed to be related to the trailing edge/jet plume interaction. At NPR = 3.0, strong screech tones are mitigated with the surface installed at h = 0De. In the shielded region, noise levels are significantly lower for all plate positions. Mixing noise and Mach wave radiation are affected by the plat stand-off location at the ϕ = 90o. Heated jet measurements up TR = 3.0, near-field and high-speed shadowgraph visualization are performed and reported.