Experimental Studies of Open Cavity Configurations at Transonic Speeds with Flow Control

摘要

CHANGES in mean static pressure distributions inside a cavity can result in large pressure gradients, and the unsteady flow disturbances can generate self-sustaining oscillations that, in turn, generate acoustic tones that radiate from the cavity. Both the steady and the unsteady flows can present difficulties for store separation from an internal weapons bay. The steady flows can generate large nose-up pitching moments, and the unsteady flows can induce structural vibration. To ensure safe carriage and separation for transonic and supersonic speeds, a better understanding of the physics of cavity flows must be obtained. Little research has been performed on closed cavities, and even less in transitional cavities. First, they occur less often because of the size of weapons. Second, there are more complex types of flow structure and problems regarding open cavities. Finally, the flow structure in cavities has in general been assumed as two-dimensional. So the closed cavity flow can be assumed as the same as flow over a backward-facing step followed by flow over a forward-facing step. Roshko [1], Krishnamurty [2], Rossiter [3], and Sarohia [4] are some of the early investigators that studied the resulting flowfield inside cavities. Rossiter [3], in 1964, proposed a semiempirical formula for predicting the frequency peaks in high subsonic compressible flows over cavities with a length-to-depth ratio L/D> 1. Noting that the characteristic frequencies vary proportionally to Ux and inversely to L, he plotted the Strouhal numbers Stn = fnL/U^, against the flow Mach number for various cavity configurations.