Measurements of Resonance in a Forward-Facing Cavity at Mach Six

摘要

An experimental study of the resonance of a cylindrical forward-facing cavity was conducted in a Mach 6 quiet-flow wind tunnel. The diameter of this cavity was fixed and the depth was varied in order to find the critical depth at which the cavity resonance became self-sustained. At Mach 6, this critical depth was 1.2 diameters deep, regardless of the freestream noise levels. For cavities deeper than 1.2 diameters, measurements of root-mean-square pressure fluctuations were orders of magnitude larger than those in shallower cavities. In quiet flow, this increase was about 2.5 orders of magnitude. In noisy flow, this increase was only about one order of magnitude. However, the magnitude of the pressure fluctuations within deep cavities was about the same in quiet flow as it was in noisy flow. The damping characteristics of a shallow cavity (depth less than 1.2 diameters) were also studied by observing the cavity response to a freestream laser-generated perturbation. The perturbation convects with the flow and interacts with the model's flowfield, causing pressure fluctuations in the forward-facing cavity. These pressure fluctuations damp exponentially in shallow cavities. The damping characteristics of such cavities appear to be related to the nondimensional cavity depth, regardless of stagnation pressure, stagnation temperature, and Mach number.