Скачать или смотреть Receptivity at the nozzle lip of underexpanded supersonic impinging jets

The receptivity of an under-expanded supersonic impinging jet flow at the sharp nozzle lip to acoustic impulse disturbances is investigated as a function of geometric and flow parameters. Receptivity in this study is defined as the internalisation of an external disturbance into the initial condition that either initiates or sustains a vortical instability. In the case of under-expanded impinging jet flow subjected to an acoustic disturbance this transfer function is located at the nozzle lip and thus, is amenable to an impulse response analysis using the linearised compressible three-dimensional Navier-Stokes equations. In this study, the transfer function at the nozzle lip is defined as the ratio of the output flow energy to the input acoustic energy of the acoustic disturbance. The under-expanded supersonic jets emanate from an infinite-lipped nozzle with a nozzle pressure ratio of 3.4 for two nozzle-to-wall distances (h) of 2 and 5 jet diameters.

It is found that for both cases, acoustic disturbances located at angles greater than 80o from the jet centreline have the highest receptivity for all azimuthal mode-numbers investigated, except the azimuthal mode-number 2 in the case of h=5d. The case with h=5d is found to also have high receptivity to acoustic disturbances located at angles between 15 and 50 degrees from the jet centreline for acoustic disturbances of all azimuthal mode-numbers.