SYNOPTIC: Drag of Rectangular Cavities in Supersonic and Transonic Flow Including the Effects of Cavity Resonance,

Abstract

The drag of relatively short rectangular cavities (length-to-depth ratios of 0.50-3.0) with turbulent shear layers has been measured at transonic and supersonic Mach numbers (0.33.0). Of particular importance is the effect of pressure oscillations within the cavity (commonly referred to as cavity resonance) which is shown to increase the drag as much as 250%. Cavity resonance is found to occur over the entire Mach number range investigated and other work has shown it to occur at both lower and higher Mach numbers. The frequency of the pressure oscillations is best predicted by the vortex-wave interaction model presented by Rossiler. The effects of external reinforcement of resonance by reflection of radiated pressure waves are examined both experimentally and analytically. Existing methods for predicting cavity drag are inadequate to cope with this phenomena. A new model for predicting the lower bound of cavity drag (nonresonating cavity) is presented and agrees well with experimental data. Analytical considerations are utilized to indicate the qualitative effect of resonance on cavity drag.