Abstract
The receptivity of an underexpanded supersonic impinging jet flow at a sharp nozzle lip to acoustic impulse disturbances is investigated as a function of geometric and flow parameters. The underexpanded supersonic jets emanate from an infinitelipped nozzle, i.e. the nozzle exit is a circular hole in a flat plate. Two specific cases have been investigated corresponding to nozzletowall distances of h = 2d and 5d, where d is the jet diameter, at a nozzle pressure ratio of 3.4 and a Reynolds number of 50 000. Receptivity in this study is defined as originally coined by Morkovin (Tech. Rep. AFFDL TR, 1969, pp. 68149; see also Reshotko, AGARD Special Course on Stability and Transition of Laminar Flow, N8433757 2334) as the internalisation of an external disturbance into the initial condition that either initiates or sustains a vortical fluid dynamic instability. Notionally, receptivity can be considered as a transfer function between the external disturbance and the initial conditions of the vortical instability. In the case of underexpanded supersonic 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 threedimensional NavierStokes 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 sensitivity of this transfer function to the angular acoustic disturbance location, its azimuthal mode number and Strouhal number has been investigated for the two underexpanded supersonic impinging jet flow cases. It is found that for both the h = 2d and 5d cases, acoustic disturbances located at angles greater than 80° from the jet centreline, with Strouhal numbers in the range between 0.7 and 6.5, 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° from the jet centreline for acoustic disturbances of all azimuthal mode numbers.
Original language  English 

Article number  A27 
Number of pages  22 
Journal  Journal of Fluid Mechanics 
Volume  889 
DOIs  
Publication status  Published  25 Apr 2020 
Keywords
 compressible turbulence
 instability control
 shear layer turbulence
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