Characterization of Flow Over and Downstream of Deep Rectangular Cavities at Subsonic Speeds

摘要

Cavity wake behaviors have not been studied in detail and are a major concern for air vehicle integration of cavity-based (e.g., open port) optical sensors. This research focused on flow over deep cavities at subsonic speeds with emphasis on the cavity shear layer and its transition to a wake downstream of the cavity. The experimental wind tunnel test apparatus developed for this study included a variable depth cavity in a boundary layer splitter plate/fairing assembly, a 2 axis traverse, and a pitot rake with in-situ pressure transducers for high frequency response. Flows were measured over clean cavities and cavities with a leading edge porous fence. Cavity length to depth (L/D) ratio was varied from of 4 to 1/2. Streamwise and cross-stream flow sections were measured to three cavity lengths downstream of the cavity trailing edge. Wake boundary layer thicknesses were roughly twice those of a flat plate turbulent boundary layer (TBL). Lateral TBL thickness distributions showed asymmetries and peaks that may be related to the three dimensional flow effects from cavity length to width ratios and resonance state. The porous fence suppressed all resonances except at L/D=1 where there was ～30 dB reduction of the peak versus the clean cavity. Turbulent intensities (TI) for both configurations were 35% to 55% with momentum thicknesses of 1.7 to 2.3 that of a TBL. Momentum thicknesses and TI's decayed to near that of a TBL by 3 lengths downstream of the trailing edge for both clean and fence configurations. This result provides an indication of the region that would be of greatest interest for the air vehicle integrator.