Bubble Induced Flow Topology Changes in Cross Flow over a Cylinder*

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 (up to a void fraction of 10%), the parameter space spanned by bubble size, Reynolds number, and void fraction has only been partially explored. We explore Reynolds numbers from 100,000 to 360,000 at void fractions from 0 to 0.04%. The injected bubbles range from 0.2 to 1 mm in size, with a volumetric mean diameter of roughly 0.3 mm. POD and SPOD analysis is used to identify structures and dominant frequencies present in the multiphase flow, which are compared to PIV measurements of the single-phase velocity field. In contrast to previous literature which predominantly indicates a shedding frequency increase, we find a non-monotonic shift in the shedding frequency when varying the void fraction and Reynolds number. The shedding frequency is decreased for the subcritical regime, and there are indications that a premature shift to the drag crisis can be induced for certain parameter ranges. Changes to the eddy length and recirculation length are also presented.