High Void Fraction Experiments in Bubbly Vortex Shedding

Vortex shedding in bluff-body flows can affect the performance of many devices such as hydrofoils and heat exchangers. Past experiments have observed that introducing bubbles in the carrier liquid can increase the shedding frequency. Building off low void fraction (α < 0.01%) one-way coupled flow experiments, we increase the gas injection to achieve void fractions of up to 10% to observe the vortex street in a two-way coupled regime and further understand the mechanics behind the frequency shift. Flow in a 100mm square channel over a 25mm circular cylinder at Reynolds number up to 25,000 is examined. A needle array with liquid co-flow controlled independently from the bulk flow is used to control the diameter distribution of O(mm) nominally monodisperse bubbles, as previous findings suggest bubble diameter affects the shedding frequency. High-speed cameras and optical probes are used to characterize the preferential concentration of bubbles, while pressure transducers will record the shedding frequency. Additional bluff body geometries will also be used to explore the impact of flow separation on bubble preferential concentration.