Book Description

An experimental investigation was conducted of subsonic turbulent flows over shallow, axi-symmetric cavities located downstream of the leading edge of a flat-nosed fuse contour and on an ellipsoidal nose contour. The objective was to evaluate cavity performance in terms of pressure oscillations inside the cavity for various cavity configurations and other pertinent parameters for various modes of cavity operation. Free-stream velocities over the contours ranged up to 650 ft/sec, and Reynolds numbers based on maximum diameter of the contour ranged between 10000 and about 1000000. It was found that pressure signals at the base of the cavity for an oscillating cavity flow as high as 150 dB, could be obtained and that a total acoustic power as high as 20 W was estimated. Furthermore, pressure oscillations existed for cavity depths as small as 0.050 in. It may be that this is not the minimum depth for which oscillations are generated, since the next smaller depth tested was 0.020 in. For the smallest depth, of 0.020 in., pressure oscillations in the cavity did not occur. Cavity oscillations were more pronounced when the cavity was located in the favorable (negative) pressure gradient region of the axi-symmetric body. Instant spark shadowgraphs taken for both laminar and for turbulent boundary layer flow separation at the upstream cavity corner showed the presence of large, organized vortex structures in the oscillating shear layer. Mean velocity measurements of an oscillating cavity shear layer indicated an entrainment rate as large as 0.046 as compared to a non-oscillating cavity shear layer entrainment of approximately 0.021.