Date of Award

Fall 1991

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Mechanical & Aerospace Engineering

Program/Concentration

Mechanical Engineering

Committee Director

Gregory V. Selby

Committee Member

Dennis M. Bushnell

Committee Member

Oktay Baysal

Call Number for Print

Special Collections; LD4331.E56K575

Abstract

The transition behavior of a free shear layer above a cavity with high and low levels of freestream acoustic disturbances has been investigated at Mach 3.5 in the Supersonic Low-Disturbance Pilot Tunnel located at NASA Langley Research Center. Schlieren photography, mean pitot pressure data, and hot-wire surveys were used to detect transition locations. The transition Reynolds numbers obtained were between ReTr = 3.6 x 105 and 5.3 x 105 in good agreement with conventional ("noisy") wind tunnel results. The study indicated that the effects of a decrease in freestream noise on ReTr were minimal but, as expected, favorable (higher ReTr). However, hot-wire anemometry data indicated that the shear-layer disturbance growth differed considerably for high and low noise levels. Also, the growth frequencies are considerably below expectations based on linear stability theory. Correlations between hot-film sensors mounted on the cavity floor indicated the presence of disturbances, believed to be vorticity and/or entropy waves, convecting upstream at about 7.2 to 11.5 percent of the freestream velocity. Upstream convected disturbances (acoustic as well as the aforementioned vorticity/entropy waves) are believed to be at least partially responsible for the insensitivity of ReTr to the freestream acoustic disturbance field.

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DOI

10.25777/44n4-5r81

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