Nozzle Throat Optimization on Acoustics and Performance of a Supersonic Jet

Nozzles used in supersonic flight applications have flow contours that cause the flow to differ from isentropic nozzle flow, resulting in less than ideal nozzle performance. The impact of nozzle contour on performance is well quantified, however it is less clear how the nozzle contour affects supersonic jet noise. This work investigates differences in noise characteristics of a sharp throat and contoured throat nozzle to identify the dependencies of supersonic noise components on the nozzle design. The nozzles are designed to be thrust matched at fully expanded conditions. The throat contour does not significantly affect the acoustics at fully expanded conditions, although the nozzle efficiency is increased for the contoured throat nozzle. Contouring the throat causes the nozzle to have screech instabilities over a broader range of operating conditions when imperfectly expanded. A detailed PIV and LES investigation was used to explain the acoustics behavior at all conditions. Reducing the throat shock strength increased the nozzle exit shock strength and periodicity, subsequently increasing the susceptibility to screech. Nozzle performance is increased at all operating conditions with the contoured throat nozzle