An Experimental Investigation of 2-D Cylinders Affecting Supersonic Cavity Flow

摘要

Experiments were performed at nominal Mach Number 1.8 to better understand the mechanism of suppression of resonant tones caused by supersonic flow over an open cavity of L/D = 4.88 and LAV = 3.67. Much attention has been paid to the rod in crossflow because of its well-known ability to shed vortices at some Mach numbers and geometric conditions. A number of researchers have attributed the effectiveness of the rod to high frequency excitation due to spanwise coherent vortex shedding. This subsequently reduces the instabilities within the shear layer and the resonant tones within the cavity. To investigate this theory, other 2-D cylindrical models, designed specifically to inhibit vortex shedding, were experimentally compared with the rod. Several models, orientations and positions were tested, all at the same height from the cavity leading edge. Pressure spectra, particle image velocimetry and schlieren photography was carried out to measure and evaluate the effect of each model. The effects of cross sectional shape and horizontal position (within 4d of cavity leading edge) were found to be minimal. Models that are known to inhibit vortex shedding, such as a rod with a long splitter plate (tail), were just as effective as the rod. As designed, a supersonic airfoil model developed the thinnest wake and did not perform as well as the rod models of equivalent thickness. The cavity leading edge and trailing edge pressure sensors did not detect a vortex shedding frequency, in any of the tested configurations. In this study, vortex shedding in the wake of the 2-D cylinders was not detected or any other frequency dominated process affecting the measured suppression levels. Results indicate that the suppression of resonant tones is linked to wake effects. Each body's wake size and relevant trajectory above the cavity trailing edge dominate the body's effectiveness in cavity tone suppression.