Nonlinear Feedback Mechanisms Inside a Rectangular Cavity

Abstract

An examination of a rectangular cavity with a length-to-depth ratio of 5.67 was tested at Mach 0.7 and 1.5 with corresponding Reynolds numbers of and , respectively. High-speed shadowgraph movies were simultaneously sampled with dynamic pressure sensors at 75 kHz. From the high-speed shadowgraph movies, observations of the cavity flowfield indicate that linear models like Rossiter’s equation and Helmholtz resonance may be too simplistic to correctly model rectangular cavity flow physics. Some of the observations are as follows. In the cavity’s shear layer, large-scale vortices have been found to be nonperiodic. The shear-layer convection velocity was determined to be at both Mach numbers, which is significantly higher than Rossiter’s equation predicts for correct peak frequency matching. Shear-layer entrainment of freestream flow starts and feeds the acoustic cycle inside the cavity. There are more acoustic wave in the cavity at any one time than has been considered before, which produce the discrete acoustic tones throughout the frequency spectrum.