Effects of a base cavity on subsonic near-wake flow

Abstract

An experimental investigation has been conducted to study the effects of a base cavity on the near-wake flowfield of a slender, two-dimensional body in the subsonic speed range. Three base configurations were investigated and compared: a blunt base, a shallow rectangular cavity base of depth equal to one-half the base height, and a deep rectangular cavity base of depth equal to one base height. Each configuration was studied at three freestream Mach numbers ranging from the low to high subsonic range. Schlieren photographs revealed that the basic qualitative structure of the vortex street was unmodified by the presence of a base cavity. However, the vortex street was weakened by the base cavity apparently due to the enhanced fluid mixing occurring at the entrance of the cavity. The weaker vortex street yielded higher pressures in the near wake for the cavity bases, increases in the base pressure coefficients on the order of 10-14%, and increases in the shedding frequencies on the order of 4-6% relative to the blunt-based configuration. The majority of the observed changes occurred in going from the blunt base to the shallow cavity base.