Aerodynamically induced resonance in rectangular cavities

Abstract Experiments have shown that in deep rectangular cavities of large aspects ratios at low Mach numbers oscillations of discrete frequencies can be produced. These oscillations are primarily of the fundamental acoustic depth mode and the values of the non-dimensional quantity ( fd a ) are in close agreement with a published theory. An additional shear layer resonance is inferred from the fact that the noise level reaches obvious maxima at certain Mach numbers, yielding two bands of Strouhal numbers with a suggestion of a third. The similarity between this shear layer flow and that of edge tones is supported experimentally. Thus the phenomenon of aerodynamically induced cavity resonance is considered to result from the simultaneous doubly tuned amplification of the shear layer unsteadiness by both the shear layer “edge tone” effect and the cavity enclosure acting as an acoustic resonator.