Passive Control of Supersonic Shear Layer in Rectangular Multistream Jet

Abstract

Supersonic multistream engines with single-expansion ramp nozzles use splitter plates to separate the core from bypass streams. The resulting shear-layer instability imposes unsteady loading on proximal surfaces and generates acoustic tones. The present work develops a passive control strategy to alleviate these effects. The thick splitter plate subcomponent of the full configuration is isolated, and Mach 1.6 and sonic boundary layers are allowed to develop on either side to form the shear layer. Instability mechanisms and optimal forcing-response characteristics are identified from linear analysis of time-averaged large-eddy simulations (LESs). These results are then used to guide splitter plate trailing-edge modifications with different wave numbers and amplitudes to interfere with the internal forcing mechanism. LESs of the altered configurations at small wave numbers reveal a diamond-grid-like pattern of cells and dislocations, similar to those observed in low-speed active control studies. Modal decomposition displays an increase in rank behavior, with the dominant mode in good agreement with linear predictions. At large wave numbers and amplitudes, where nonlinear effects are stronger, LESs show that control introduces streamwise vorticity into the wake, reduces coherent structure size (streamwise correlation length) and inhibits the tonal content. These effects are confirmed in companion experiments.