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Passive Control of Supersonic Rectangular Jets via Nozzle Trailing-Edge Modifications

A research program was carried out to explore the effects of nozzle trailing-edge modifications on the flow structure, jet mixing with the ambient air, and jet noise of a rectangular supersonic jet. Nozzles with one modified trailing edge were used with the intention of enhancing mixing and reducing noise. The modifications were simple cutouts in the plane of the nozzle wall and acted to induce large-scale streamwise vortices. A rectangular jet, with a design Mach number of 2 and with various trailing edges, was examined using optical diagnostics and noise measurements in flow regimes ranging from moderately overexpanded M j =1.5 to moderately underexpanded M j = 2.5. In nonideally expanded flow regimes, one could generate pairs of streamwise vortices of various strength and sign and that the mixing could be significantly enhanced. The modifications could eliminate or at least substantially reduce screech noise and could significantly decrease the overall far-field sound pressure level in the nonideally expanded flow regimes. In the ideally expanded flow regime, the trailing-edge modifications did not seem to induce streamwise vortices and, thus, did not have a substantial effect on the jet mixing or noise