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ANSYS 2019 R3

How to Build a Cavitation Model Using CFD and Overset Meshes

The local temperature and pressure differentials caused by cavitation can erode nozzles, propellers and turbines. Engineers can use overset meshes to simplify the simulation of this phenomenon.

Hydraulic cavitation can cause a lot of damage to a nozzle, propeller or turbine. These tiny bubbles may not look like much. However, their local temperature and pressure differentials can be so high that they erode metal components.

As a result, engineers need to design underwater mechanical parts so they don’t create cavitation bubbles as they move.

The challenge is that modeling cavitation in computational fluid dynamics (CFD) simulations can be challenging and time-consuming.

The simulation requires a fine mesh in the cavitating zone. Since these areas are often associated with complex moving geometries, creating this mesh requires a lot of skill.

Engineers studying cavitation can build an overset mesh in ANSYS Fluent to simplify the simulation process. Overset meshes consist of component grids that layer on top of each other. The meshes can move independently — changing the flow domain. The overset mesh enables engineers to study cavitation by capturing a system’s intricate geometry, flow domain and movement.

Overset Meshes Simplify Alterations to the Flow Domain when Assessing Cavitation

Overset meshes are able to capture the behavior of complex moving geometry without remeshing the flow domain.

The rotations of an overset mesh with three overlapping zones

Fluent’s overset mesh feature partitions the grid into sub-domains and combines them with overset interfaces and patched interfaces. The software then deactivates any overlapping element that isn’t participating in the current iteration of the simulation.

With each iteration, the cells at the border of the sub-domains trade information with other bordering cells. Once the solution for the current iteration is solved, the mesh movements are carried out and the process repeats.

The fluid in the simulation is governed by a standard viscous flow equation and a conventional turbulence model. The cavitation is modeled using a liquid-vapor mass transfer and vapor transport equation.

To learn how to build an overset mesh, watch the video below or read: Overset Mesh Can Simplify and Speed Simulations with Moving Parts.

This video shows how to build an overset mesh.
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