Flow Around an Object Projected from a Cavity Into a Supersonic Freestream

The pressure and flow field of a supersonic flow over a cavity, with and without a store, was the focus of this experimental investigation. A single cavity geometry, with a length to depth ratio of 3.6 was studied while the freestream Mach number and the placement of the store relative to the cavity floor were varied. The traits of the pressure spectra on the cavity floor were markedly different between freestream Mach numbers of 1.8 and 2.9. While the Mach 1.8 case exhibited clear spectral peaks consistent with predictions by Rossiter, the Mach 2.9 flow field did not. With the store placed within the free shear layer, the level of pressure fluctuations measured on the cavity floor decreased for the Mach 1.8 case and increased for the Mach 2.9 case. High-speed Schlieren photography was used to visualize the interaction of the free shear layer and the modeled store. Images revealed that flow structures in the free shear layer of the Mach 2.9 flow exhibited less spanwise coherence than their Mach 1.8 flow counterparts. Images also revealed vertical displacement of the free shear layer as the store traversed through it. Pressure-sensitive paint (PSP) was utilized to quantify the full-field mean pressure on the cavity floor and store. A pressure rise near the trailing edge was noted for both freestream Mach numbers. The mean pressure contour of the floor for the Mach 1.8 case exhibited considerable three-dimensionality, despite the generally spanwise coherent structures in the free shear layer. The store exhibited asymmetry in the pressure field and a strong dependence on its vertical position. The pressure fields were then integrated over the area of the store, resulting in the calculation of the aerodynamic coefficients.

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