Book Description

Analysis of an open cavity shear layer when exposed to different leading edge pin configurations was studied experimentally, in a blow-down high speed wind tunnel run at Mach 1.84. A non-intrusive quantitative flow measurement system, Particle Image Velocimetry, was used to study velocity and vorticity fields with and without flow control implementations. The purpose of this study was to attempt to understand and explain the flow mechanisms which cause acoustic suppression obtained using different leading edge, vertical pin configurations. The cavity had an L/D of 4.89 and each pin configuration had a varied number and placement of pins, while pin height remained a constant 1⁄2 inch. The four configurations chosen to be studied were based on the best acoustic suppression results obtained by Milne [4]. To determine and understand the physical mechanism and source of attenuation of this type of cavity flow control technique, this study looked at the acoustic spectrum, velocity vector field data as well as the changes in the velocity and vorticity fields created by each pin configuration. It was determined that a redistribution of the velocity and diffusion of the vorticity in the boundary layer was caused by altering the characteristics of the boundary layer. Vertical pin configurations at the leading edge of a cavity resulted in flow characteristics which bring about a thickening of the shear layer which diffuses the boundary layer vorticity. Certain pin configurations result in various changes in the boundary layer velocity and vorticity redistributions, affecting the shear layer diffusing the boundary layer vorticity. Configurations using staggered pin patterns generated more effectively vorticity diffusion in the shear layer, which lowered the peaks and the broadband in the SPL spectrum. Possible configurations for future testing are also recommended to further study the flow suppression mechanisms.