Cavitation: Axial Inducer

Cavitation Flow Through an Axial Inducer CFD Simulation, ANSYS Fluent Tutorial

Description

This project simulates cavitation flow through an axial inducer using ANSYS Fluent. Cavitation is the phenomenon by which vapor bubbles form in regions of a fluid where local pressure drops sufficiently low. While it's often assumed that liquid pressure reaching vapor pressure (Pv) is the sole cause, several other factors — velocity being a particularly significant one — also contribute to cavitation onset. The resulting bubble collapse can cause substantial problems, including corrosion, which is especially evident in water pumps, and is typically identified through the characteristic sound and mechanical vibration it produces.

Several strategies help reduce cavitation, including increasing pump inlet pressure by reducing the distance between the pump and its supply tank, or reducing pressure drop and flow turbulence more broadly. As industry increasingly demands smaller, higher-speed pumps, improving impeller suction performance has become correspondingly more important. Inducers are components installed ahead of the main impeller, rotating at the same speed, specifically to boost inlet pressure and improve suction performance — making cavitation reduction one of the primary reasons inducers are used in pump systems.

The geometry was designed in Design Modeler and meshed in ANSYS Meshing using an unstructured grid totaling 938,174 cells.

Methodology

The inducer's rotational motion was defined using the Frame Motion method, with the fluid surrounding the inducer blades assigned a rotational speed of 15,000 rpm. Since cavitation fundamentally involves a phase change between liquid and vapor, a multiphase model was required — specifically the VOF model, chosen for its ability to sharply resolve the separation boundary between the two phases, with liquid defined as the primary phase and vapor as the secondary phase.

Conclusion

Results include contours of velocity, pressure, and liquid/vapor mass fraction, along with streamlines around the inducer. The results show that fluid pressure increases as it passes through the inducer — if connected to a pump, this represents the inducer's output pressure and the maximum pressure delivered to the downstream impellers. Suction pressure at the back of the inducer also increases, directly improving the pump's overall suction performance.

Velocity contours and streamlines show peak velocity occurring near the inducer, driven by its angular rotation, while volume fraction contours confirm a reduction in cavitation — with the proportion of liquid water present substantially exceeding that of vapor, indicating that the inducer successfully suppresses cavitation formation as intended.