Cavitation Flows

Cavitation is a phenomenon in which small cavities are generated in a liquid.  It occurs when the local static pressure is lower than the vapor pressure of the gas dissolved in the liquid.  Cavitation is the main reason for mechanical erosion.  The shock wave that occurs during the collapse of small cavities can cause strong stress and impact on the surface of metals, which leads to the formation of wears.  However, cavitation also has various useful applications.  In industry, cavitation is used to homogenize and mix chemical compounds.  In the biomedical area, cavitation can be used in a shock wave lithotripsy to destruct kidney stones.  Moreover, cavitation is a good cleaner.  One can use the acoustic technique to generate cavitation in a fluid to help remove the surface contaminants.

Supercavitation is a special type of cavitation flows.  It uses a bubble of gas inside a liquid large enough to encompass an object traveling through the liquid so that the skin friction on the object can be greatly reduced and high speed can be obtained, which can be a revolutionary step in the development of fast underwater vehicles.  To simulate supercavitation accurately, we use a multi-fluids simulation method to capture the complex air and water mixed flows and resolve the interface between the two phases.  The simulation is performed on an Eulerian grid, with the air and water treated as a coherent system with varying physical properties.  We combine the methods of level set, volume of fluid, and ghost fluid to take their advantages in the accurate representation of surface geometry, mass conservation, and sharp interface representation, respectively.  To capture the complex geometries of submerged cavitator, we use an immersed boundary method in the simulation.  Appropriate body force is applied at grid points near the surface of the cavitator to satisfy the boundary condition, with wall-layer modeling for high Reynolds number turbulent boundary layer.  The interface between the solid and the fluid is sharp so that the resolution of the flow field near the cavitator is improved.  We study supercavitation in various complex environments, including deep water flows, turbulent flows, and near-ocean surface flows.  By studying flow statistics inside the supercavity, near the shear layer between water and air, and near the rear closure structure of the supercavity, we aim to develop reduced-order models for realistic applications.

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Supercavitation in deep water
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Synthetic turbulence impacting on supercavity
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Supercavitation under ocean surface