Installed jet noise reduction using a zigzag vortex generator

In this paper, an experimental investigation into a vortex generator ring is performed to establish its potential as a noise reduction technology for next generation of closely coupled engine-airframe aircraft. A zigzag ring was 3D-printed onto the internal surface of a round, single-stream nozzle upstream of the nozzle exit plane. Isolated and installed jet configurations were studied under static and in-flight ambient flow conditions. Unsteady pressure measurements were performed using both a linear far-field microphone array and an azimuthal near-field microphone array. Unsteady velocity data at the jet nozzle exit were acquired via hot-wire anemometry. Far-field acoustic data show that the lip treatment produces a 1 dB overall sound pressure level reduction on the jet mixing noise source. The maximum benefit for this particular noise source occurs at low jet polar angles. A greater noise reduction, in excess of 3 dB, is observed for the installed configuration, where the maximum benefit is seen at forward arc polar angles. The presence of forward flight slightly reduces the overall noise advantage provided by the vortex generator. The unsteady velocity data suggest that the zigzag ring does not alter the aerodynamic performance of the nozzle significantly, but further investigation into potential thrust penalties is necessary.