Vortex Shedding in a Dispersed Multiphase Flow

Vortex-induced vibration from cross flow over bluff bodies is an important design consideration in devices from flow meters to nuclear reactors. While past researchers have shown that introducing bubbles to the flow can decrease vibration amplitude while increasing shedding frequency, the nonlinear shift in shedding frequency with bubble size has not been explained. Through experimental and numerical study of size-dependent bubble transport, we describe the mechanism causing this change in shedding frequency. The motion of monodisperse bubbles (range of 40-400 microns) introduced upstream of a cylinder is studied in 3D using tomographic bubble tracking; the flow field at the centerline plane is determined simultaneously with 2D-3C stereo PIV. The experimental results are used to validate a one-way coupled point-particle tracking model, for which the flow field is computed using high-order LES. The model is used to produce statistics on the size-dependent bubble motion in the wake of the cylinder. These statistics provide insight into the mechanism for frequency shift, which will be confirmed in higher phase fraction flows that are no longer one-way coupled.