Compressibility effects and vorticity structure of a vortex-dominated wake using volumetric reconstruction

Abstract

The effects of edge geometry and compressibility on the wake of a slanted afterbody model with rounded edges, relevant to cargo aircraft and high-speed train applications, are investigated through detailed experimental observations of the flowfield. The wake flow features are examined using centerline planar PIV measurements and novel Scanning-SPIV measurements to reconstruct the full mean volumetric velocity field. Planar PIV measurements at the model centerline reveal that increasing the Mach number reduces the shear layer growth rate, leading to decreased entrainment within the recirculation region. Consequently, the recirculation region increases in both length and height. Further downstream, the vortex circulation for the rounded-edge model remains nearly constant across both incompressible and compressible Mach numbers. Additional vortex properties are examined through the Reynolds-averaged vorticity transport equation applied to the volumetric flowfield measurements, revealing an increase in x-vorticity compression within the recirculation region. By Helmholtz’s vortex theorem, this increased vortex compression contributes to the growth of the recirculation region between Mach number conditions. Additionally, the dilatation term was explored, allowing for the delineation of compressibility effects on the recirculation region.