Effects of Initial Shear Layer State on Screech in a Rectangular Jet

Jet screech from a 4:1 rectangular nozzle at under-expanded supersonic conditions is studied using high-fidelity large-eddy simulation data. By creating a small groove on the nozzle surface, we numerically modify the boundary layer and the jet initial shear layer. A total of 5 cases with different groove sizes are studied in comparison with the no-groove baseline case. The tripping method increases the turbulent kinetic energy and boundary layer thickness at the nozzle exit. The modification in the initial shear layer leads to different shear layer thicknesses and shock cell decay rates near the end of the jet potential core. The screech amplitude is varied in the tripped cases, with largest difference measured to be 2.9 dB compared to the baseline value. The dominant coherent structures associated with screech generation are studied with spectral proper orthogonal decomposition. The amplitudes of the guided upstream-traveling wave and the downstream-traveling Kelvin-Helmholtz wave are calculated. The differences in the screech tone amplitude are found to be related to the strength of the Kelvin-Helmholtz wave, due to the modified receptivity of the initial shear layer. The gain of the guided upstream-traveling wave from the K-H wave and shock interaction is estimated.