ERI: Cavitation Bubble Dynamics Near Mixed Solid-Gaseous Surfaces

Vaporous cavitation is a rapid and temporary phase change that occurs when a liquid moves at high velocity. High flow velocities occur in, valves, pumps, hydraulic tools, hydro-turbines, and ship propellers. The high flow velocity decreases the local pressure sufficiently to cause the liquid to vaporize and form small bubbles that collapse after the pressure rises again. When a cavitation bubble collapses near a solid surface it forms a liquid jet directed toward the surface which causes the bubble to migrate in that direction. If the jet impinges on the surface or the bubble collapses directly onto it, then undesirable consequences occur. These consequences include surface damage that increases operational costs and reduces efficiency, undesirable structural vibrations, and high levels of noise, which can harm nearby people or animals. While rigid solid surfaces attract cavitation bubbles, gaseous surfaces repel them. A few scientific studies show that solid surfaces with gas-filled holes can repel a collapsing cavitation bubble, but the parameter space explored in these works is minimal and insufficient to develop bubble repellent surfaces. Therefore, the principal aim of this project is to study a wide parameter space of solid surfaces with gas-filled holes to find optimal surface geometries that repel cavitation bubbles and prevent cavitation damage, undesirable noise, and undesirable structural vibrations. The high-speed videos resulting from this work will also be used to develop educational videos that describe cavitation bubble dynamics to the public on YouTube. The goal of this project is to understand when mixed solid-gaseous surfaces repel cavitation bubbles. To accomplish this, cavitation bubbles will be formed with a pulsed laser next to a surface that consists of a rigid solid material with air-filled holes. Bubble jetting and migration behaviors will be studied using high-speed photography with the objective to measure and model the cavitation bubble collapse and migration dynamics near a solid surface with a single gas-filled hole, or an array of gas-filled holes. Bubble behaviors will be mapped to find regions of bubble repulsion, and theoretical models will be created to predict the bubble behavior transitions. These models can then be used to design novel cavitation bubble repelling surfaces that prevent damage, noise, and undesirable vibrations. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.