Sphere Release from a Rectangular Cavity at Mach 2.22 Freestream Conditions

Abstract

Experimental and computational methods were used to investigate the characteristics of a scaled, generically shaped weapons internal carriage and separation bay with a length-to-depth ratio of 4.5 at multiple Mach numbers and stagnation pressures. Three new nozzles were designed, manufactured, and characterized for the U.S. Air Force Institute of Technology small supersonic tunnel, yielding freestream Mach numbers of 1.43, 1.84, and 2.22. In addition, a control valve was reconfigured to achieve stagnation pressures as low as 1.0 psia, allowing more realistic scaling. These nozzles were used in conjunction with piezoresistive pressure transducers and high-speed schlieren photography to capture the time history of the pressure and the acoustic spectra of the cavity. The nominal Mach 2.3 nozzle was used in free-drop testing of a 1:20 scaled sphere and compared with computational simulations. The computational solution was obtained using the OVERFLOW solver with incorporated six-degree-of-freedom motion and the delayed detached-eddy simulation/shear stress transport hybrid turbulence model. Analysis of the schlieren video generated by the experimental tests allowed direct comparison of computational and experimental trajectories. Measured trajectories compared closely to computational trajectories, especially for the lowest stagnation pressure settings, where heavy Mach scaling yielded operationally relevant conditions, despite the small scale of the tests.