Flow around an object projected from a cavity into a supersonic freestream.

Store-cavity interaction was investigated by using fast-response pressure transducers, high-speed schlieren photography, and pressure-sensitive paint (PSP) at freestream Mach numbers of 1.8 and 2.9. The influence of Mach number on the interaction of a cavity (LID = 3.6, W/D = 3.8) and a modeled store was characterized. Highspeed schlieren photography illustrated the real-time motion of coherent spanwise structures in the Mach 1.8 flow and revealed the absence of these structures in the Mach 2.9 How. The spectra measured in the Mach 1.8 flow exhibited clear resonant peaks consistent with Rossiter modes, whereas the Mach 2.9 flow did not. The mean floor pressure increased as the store was positioned nearer to the free shear layer for both Mach number conditions. Interestingly, the level of the pressure fluctuations measured on the cavity floor decreased for the Mach 1.8 case when the store was positioned in the freestream but increased for the Mach 2.9 case. PSP was applied to the cavity floor and to the modeled store. Integration of the measured pressure field on the store yielded information on the forces and pitching moment. Schlieren imaging of a modeled store exiting the cavity indicated that the free shear layer is slightly displaced by the moving store.