Passive Control of Supersonic Rectangular Jets via Nozzle Trailing-Edge Modifications

Abstract

A research program was carried out to explore the effects of nozzle trailing-edge modi cations on the ow structure, jet mixing with the ambient air, and jet noise of a rectangular supersonic jet. Nozzles with one modi ed trailing edge were used with the intention of enhancing mixing and reducing noise. The modi cations were simple cutouts in the plane of the nozzle wall and acted to induce large-scale streamwise vortices. A rectangular jet, with a design Mach number of 2 and with various trailing edges, was examined using optical diagnostics and noise measurements in ow regimes ranging from moderately overexpanded M j = 1:5 to moderately underexpanded M j = 2:5. The results indicated that in nonideally expanded ow regimes, one could generate pairs of streamwise vortices of various strength and sign and that the mixing could be signi cantly enhanced. The results also indicated that the modi cations could eliminate or at least substantially reduce screech noise and could signi cantly decrease the overall far-eld sound pressure level in the nonideally expanded ow regimes. In the ideally expanded ow regime, the trailing-edge modi cations did not seem to induce streamwise vortices and, thus, did not have a substantial effect on the jet mixing or noise.

On Mixing Enhancement via Nozzle Trailing-Edge Modifications in High-Speed Jets

“…Hysteresis in the aerodynamic coef cients for the computed solution can be observed for a lying between 17 and 19 deg. Qualitatively, these results look similar to those reported by Hoffman 1 for his experiments with the NACA 0015 airfoil for low FST.…”

Decay of supersonic rectangular jet issuing from a nozzle with diagonal expansion ramps

“…Although the use of tabs is proved to be effective in enhancing mixing of supersonic jets, it results in thrust losses due to blockage effects of these vortex generators [6]. This motivated researchers to explore alternative techniques for generating streamwise vortices to enhance mixing [7][8][9][10][11][12][13][14][15]. Effects of nozzle trailing edge modifications on the flow structure and jet mixing with ambient air were explored by Samimy et al [7] and Kim and Samimy [8].…”

“…This motivated researchers to explore alternative techniques for generating streamwise vortices to enhance mixing [7][8][9][10][11][12][13][14][15]. Effects of nozzle trailing edge modifications on the flow structure and jet mixing with ambient air were explored by Samimy et al [7] and Kim and Samimy [8]. Their results indicated that in non-ideally expanded flow regimes, pairs of streamwise vortices of various strength and sign were generated and the mixing was significantly enhanced [7,8].…”

“…Effects of nozzle trailing edge modifications on the flow structure and jet mixing with ambient air were explored by Samimy et al [7] and Kim and Samimy [8]. Their results indicated that in non-ideally expanded flow regimes, pairs of streamwise vortices of various strength and sign were generated and the mixing was significantly enhanced [7,8]. Sang [9] computationally studied mixing characteristics of underexpanded supersonic jets emerging from the plain and notched rectangular nozzles using nozzle exit boundary-layer swirl as a mean of passive flow control.…”

“…The present study is a novel attempt to combine the merits of asymmetric jets [1][2][3][4][5] and trailing edge modifications [7][8][9][10][11][12][13][14][15]. Experimental and computational investigations were carried to study the effect of diagonally wall-mounted expansion ramps in accelerating the decay of an aspect ratio (AR) 2 rectangular supersonic jet.…”