Madeleine Oliver - Dissertation Defense

Title: Asymmetric Wakes in Stratified Flows
Date: May 6, 2026
Time: 2:00 pm - 3:00 pm 
Committee: Dr. Geoff Spedding (Chair), Dr. Mitul Luhar, Dr. Ivan Bermejo-Moreno, Dr. Patrick Lynett, and Dr. Fokion Egolfopoulos
Abstract: This work investigates the combined effects of inclination and stratification on the wake of a 6:1 prolate spheroid. While stratified wakes of axisymmetric bodies have been studied extensively, far less is known about inclined configurations, where asymmetry introduces coherent vortex structures and modifies wake evolution. Stereoscopic particle image velocimetry (stereo-PIV) measurements are performed in multiple orthogonal planes. Tow speed, stratification strength, and inclination angle are varied independently, resulting in a parameter space spanning Reynolds numbers Re = (0.625−20) ×103, Froude numbers Fr = U/ND = 2−32 and ∞, and inclination angles θ = 0◦ and 20◦. In the absence of stratification, inclination generates persistent wake asymmetry and a net vertical impulse that deflects the wake trajectory. When scaled by an effective body diameter, early wake growth collapses across inclination angles, indicating that the increased wake height arises primarily from geometric effects. At sufficiently low Froude number, buoyancy modifies the near-body region by shifting the separation location and altering wake trajectory and velocity profiles. For Re = 5000, wake heights collapse across stratification strengths when scaled appropriately, while the wake exhibits oscillations at the buoyancy frequency, in agreement with previously reported stratified wake dynamics. Inclined wakes exhibit regularly spaced vertical velocity protrusions along the upper wake boundary. The spacing depends on Reynolds number but shows no measurable dependence on Froude number. Measurements in a lateral plane show that these features coincide with asymmetry in the counter-rotating vortex pair arising from deformation of the vortex cores. Finally, stereo-PIV measurements of the internal wave field show that inclination alters the spatial organization and apparent propagation of body-generated internal waves.