Influence of Mach Number and Dynamic Pressure on Cavity Tones and Freedrop Trajectories.

摘要

Weapons release at supersonic speeds from an internal weapons bay is a highly desirable capability. To ensure a successful release at multiple Mach numbers, the aerodynamic environment must be well-understood and repeatable, with a robust system for safe testing of store separation. For this reason, experimental methods were used to investigate the characteristics of a scaled WICS 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 AFIT small supersonic tunnel, yielding freestream Mach numbers of 2.22, 1.84, and 1.43. In addition, a control valve was recon gured to achieve stagnation pressures as low as 1.0 psia. These nozzles were then used in conjunction with piezosresistive pressure transducers and high-speed Schlieren photography to capture the time-varying pressure signal and spectra of the cavity. Resonant frequencies from these tests matched very well with analytically predicted results for the Mach 2.3 and Mach 1.9 nozzles. The Mach 1.5 nozzle posed some di culties for the con guration tested due to shocks re ecting into the cavity. The Mach 2.3 nozzle was utilized in freedrop testing of a 1:20 scaled sphere and compared to computational simulations. The computational solution was obtained using the OVERFLOW solver with incorporated 6DOF motion and the DDES/SST 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 results, despite the small scale of the tests.