Cavitation in Pelton Turbine, ANSYS Fluent CFD Simulation

Description

In this project, we perform the numerical simulation of the Cavitation phenomena in a Pelton Turbine in ANSYS Fluent software.

A Pelton turbine is a type of hydraulic turbine that uses the energy of water pressure to rotate a wheel with cup-shaped blades and subsequently produce the required mechanical energy.

Cavitation is a destructive phenomenon that can occur in hydraulic turbomachinery and reduce system efficiency. Whenever the fluid pressure drops below the vaporization pressure, vapor bubbles form. These bubbles then collapse due to circulation and pressure rise, creating strong shock waves to the body and blades of the turbine.

Methodology

First, we model the geometry in 3D using Design Modeler software. The computational domain is the interior of a closed chamber in which a Pelton turbine is mounted. Then, we mesh the model using ANSYS Meshing software, and about 4,136,000 cells are generated. Finally, we simulate the flow around the Pelton turbine in ANSYS Fluent software.

We use the Multi-Phase Model to define a two-phase flow, including water-liquid and water-vapor. For multiphase flow, we define the Volume of Fluid (VOF) model. Then, we define a mass transfer mechanism between the two phases in the form of the cavitation model based on the vaporization pressure. Thus, phase exchange occurs from the primary phase (water) to the secondary phase (vapor).

We utilize the Moving Reference Frame (MRF) to define a rotation flow zone. In other words, we apply rotation to the fluid region adjacent to the turbine body. Since the run calculation is in an unsteady state, we use the Mesh Motion tool with a specified rotational speed.

Conclusion

After calculations, we analyze the behavior of multiphase flow and the cavitation phenomenon.

For this purpose, we obtain the distribution of water-liquid and water-vapor phases in the vicinity of the turbine body at different times. Therefore, we obtain the contours corresponding to the volume fraction of water and vapor.

The distribution of water and vapor confirms that phase exchange occurs in zones where pressure variations are significant. Therefore, in the vicinity of the turbine blades, vapor bubbles are generated over time.

So, we can conclude that our simulation has been performed correctly.