Experimental Comparison of Unstratified and Stratified Drag Wakes of a Dimpled Sphere at Reynolds Number 105

Abstract Dated: March 16, 2025 The drag wake of a dimpled sphere is studied experimentally using Stereo Particle Image Velocimetry at Re = 10^5 in both unstratified and stratified (Froude number ≃ 80) fluids at downstream distances 2 ≤ x/D ≤ 15. More than eighty experiments were conducted, and both analysis of ensemble mean wakes and statistics of individual wake data are presented. Stratification is found to qualitatively change the ensemble-mean wake axial velocity defect immediately behind the sphere, taking a Gaussian shape without stratification and a two-lobed shape with stratification. The maximum of the ensemble mean wake defect at x/D = 2 was ∼ 0.4 times the tow speed in the stratified case, and ∼ 0.1 times the tow speed in the unstratified case.