Effect of Axial Location of Micro Vortex Generators on Supersonic Jet Noise Reduction

Abstract

Micro-vortex generators (MVGs) have been developed to reduce supersonic jet noise of model-scale faceted nozzles that are representative of GE-F404 nozzles. MVG technology has a large parametric space for optimization and the axial implementation location is a critical parameter that affects the shock-cell structure and the noise generation. To assess this axial-location effect, two axial implementation locations of MVGs with two types of blade orientations to the incoming flow have been used. One location induces a large Mach disk that weakens the downstream shock cells and reduces noise at a highly overexpanded nozzle pressure ratio, but this effect diminishes as the nozzle pressure ratio increases. Another location induces a shock-cell cancellation and this location presents a consistent noise reduction over a broad range of the nozzle pressure ratio. The location that induces effective shock-cell cancellation varies slightly with the blade height. In addition, the blade orientation of the MVG pair to the incoming flow also affects the noise reduction. MVG pairs which two blades form a divergent arrangement to the incoming flow presents a better noise reduction in the upstream direction, but those forming a convergent arrangement present a better noise reduction in the peak and further downstream directions. The noise reduction up to 5dB has been observed at a reasonable thrust penalty. Furthermore, the thrust performance of MVGs is relatively stable over a broad range of the nozzle pressure ratio. This is different from the thrust performance of chevrons, which thrust penalty increases with the nozzle pressure ratio.