Wake of falling axisymmetric bluff body in quiescent liquid

The wake of an axisymmetric rigid body (a spherical cap of base diameter D and height H) in a quiescent liquid is studied experimentally. The study considers the axisymmetric bluff body freely falling in a fluid at rest. PLIF technique is used to visualize the wake. Mass ratio m∗ (defined as the relative density of the model compared to the fluid) is always greater than one in the present study. Liquid viscosity and base diameter are varied to achieve different Reynolds numbers. As reported in literature, the sphere (mass ratio> 1) always falls without vibration. However, we observed the falling hemisphere with shedding wake to have spiral or zigzag path. We present wake dynamics of rigid spherical cap for different mass ratios (1.13, 2.7, 8.73). We further investigate the mass ratio threshold for vibrating and non-vibrating regimes and report detailed wake analysis using PIV experiment.