Experimental investigation of fluid dynamic instability in a transonic cavity flow

The acoustic and fluid dynamic resonance in a two-dimensional cavity flow was investigated experimentally. In order to visualize a periodic oscillation of the shear layer and the behavior of vortices, the schlieren method was used with an ordinary CCD camera and a high-speed video camera. Particle image velocimetry (PIV) measurements were also carried out to obtain the vorticity distribution during the oscillation in the cavity flow. Shedding and interaction of vortices in the shear layer were observed near the trailing edge of the cavity, which causes the generation of pressure waves. The feedback process of the oscillation was determined using high-speed camera images. From these results, the x − t diagram for the oscillation cycle was obtained. Based on the flow visualization, for Rossiter's constants, it was confirmed that the dominant acoustic mode was m = 2 and that Kc = 0.5 in the present experiment. Also, the pressure level for mode m = 2 was the most intense for a wide range of flow Mach numbers. The results obtained by PIV measurement show that there is outgoing and incoming flow near the trailing edge of the cavity. It was found that a very strong change of vorticity associated with the detachment and attachment of boundary layer was induced on the trailing edge due to the fluid dynamical instability.