Coherent structures in the stratified near-wake of an inclined 6:1 prolate spheroid*

Stratified wakes of various axisymmetric bodies have been well-studied where the wakes can be scaled based on the effective drag coefficient. However, non-axisymmetric wakes from a body at high incidence (e.g. inclined spheroid), complex surfaces (e.g. wingtip, fins), or a large maneuver introduces special flow structures such as strong trailing vortices that may generate patterns that can persist into the late wake. The current project seeks to investigate how these coherent structures interact with the drag wake in the presence of background stratification. An experiment is conducted on the near-wake of a towed 6:1 prolate spheroid with incidence angles θ = {0, 10, 20}° at Reynolds number based on the diameter Re_D = {0.5, 1, 2} × 10⁴ and Froude number Fr = {8, 16, 32, ∞}. To capture the complex 3D flow structure, tomographic PIV is used where a measurement depth of more than half wake width (~ 0.85D) is achieved. The averaged wake decay rate and the vortex pair propagation are compared with existing literature and described as functions of Re, Fr, and θ to find scalings that can be used to test extrapolation to higher Re, and also to provide information for potential pattern detection.