An experimental study of mixing and noise in a supersonic rectangular jet with modified trailing edg...

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" An experimental study of mixing and noise in a supersonic rectangular jet with modified trailing edges "
J.-H. Kim M. Samimy

Document Type	:	Latin Dissertation
Language of Document	:	English
Record Number	:	1113181
Doc. No	:	TLpq304457650
Main Entry	:	J.-H. Kim
	:	M. Samimy
Title & Author	:	An experimental study of mixing and noise in a supersonic rectangular jet with modified trailing edges\ J.-H. KimM. Samimy
College	:	The Ohio State University
Date	:	1998
student score	:	1998
Degree	:	Ph.D.
Page No	:	204
Abstract	:	A rectangular nozzle with design Mach number 2 and aspect ratio 3 is used to investigate the effects of various geometric modifications to the nozzle trailing edge on gas mixing and jet noise. Flow visualizations are carried out by the laser sheet illumination technique, while noise is measured by two microphones. Surface flow visualizations by the kerosene-lampblack technique and wall pressure measurements are performed to investigate the major sources of streamwise vorticity. Variation of thrust is measured by an axial thrust measuring system. In the ideally expanded case, no measurable mixing enhancement or noise reduction was observed. On the other hand, significant mixing enhancement was achieved for all modifications in the underexpanded cases. The near field mixing performance of modified nozzles, which generate kidney type pairs of streamwise vortices, were found to be better, while at farther downstream locations, nozzles which generate mushroom type pairs of streamwise vortices performed better. When the modification was used on both sides of the longer nozzle dimension, mixing enhancement was additive of that by each modification. When the jet was overexpanded, relative mixing enhancement was reduced with downstream locations because of the much enhanced mixing of the baseline nozzle due to the flapping motion. Only nozzles which generate mushroom type pair vortices showed better mixing at farther downstream locations. The mixing enhancement for nozzles with double sided modifications was almost in the same level of that for nozzles with single sided modifications. The measured wall pressure and surface flow data suggests that the major source of streamwise vorticity is most likely the spanwise pressure gradient on the modification. The reductions of the overall sound pressure level for the modified nozzles were greater for the overexpanded cases than for the underexpanded cases. These reductions are probably related to the three dimensional distortions of shock cell structure which could be inferred from the cross sectional deformations and more directly from surface flow images and pressure data. The fundamental screech mode on the minor axis for the baseline nozzle was antisymmetric at Musd\rm\sb{j}usd = 1.75. The modes for the modified nozzles were changed to oblique modes due to the modifications. Regardless of the modifications, the modes were antisymmetric both on the minor and major axes when jets were slightly underexpanded. The fundamental screech frequency measured agreed well with the theoretical value. No measurable thrust loss or gain was observed for nozzles with single or double sided trailing edge modifications. Therefore, the use of trailing edge modifications is a very promising technique, which can significantly enhance mixing and reduce shock noise with minimal thrust loss, especially in the non-ideally expanded cases.
Subject	:	Applied sciences
	:	Jet noise
	:	Mixing enhancement
	:	Modified trailing edges
	:	Rectangular jet
	:	Supersonic jet