Cavitation: Radial Flow Pump

Cavitation in a Radial Flow Pump CFD Simulation, ANSYS Fluent Tutorial

Description

This project simulates the cavitation phenomenon inside a radial flow pump using ANSYS Fluent. This centrifugal (radial flow) pump draws fluid in parallel to its central axis and discharges it radially, perpendicular to the inlet path — a configuration commonly used to generate high pressures at relatively low flow rates, and among the most widely used pump types overall.

Cavitation occurs when a liquid's local pressure drops below its vapor pressure at a given temperature, causing the fluid to transition from liquid to vapor and form bubbles. If these bubbles subsequently travel into higher-pressure regions of the pump, they collapse — this collapse generates a localized vacuum, drawing the surrounding liquid inward at very high speed and pressure, often striking nearby walls and blades with enough force to cause damage and shorten pump lifespan.

Methodology

The working fluid was liquid diesel, defined with a density of 830 kg/m³ and a viscosity of 0.00332 kg/m·s. Since pumps operate fundamentally on pressure differences, pressure boundary conditions were applied at both the inlet and outlet — diesel entered axially at 0 Pa and exited radially at 109,872 Pa. Fluid rotation within the pump was captured using the Moving Reference Frame (MRF) approach, with a rotational speed of 20 rad/s.

To specifically investigate cavitation risk, a second fluid — diesel vapor — was defined with a density of 9.4 kg/m³ and a viscosity of 0.000007 kg/m·s, using the VOF multiphase model. Liquid diesel served as the primary phase and diesel vapor as the secondary phase, with mass transfer between them governed by the cavitation model, using a vapor pressure threshold of 50,900 Pa to trigger phase change.

The 3D geometry was designed in BladeGen. Given the model's radial symmetry, only a single blade passage was modeled — featuring an axial inlet section on one side and a radial outlet section on the other, with periodic boundary conditions applied on both sides and a single blade drawn as a curved profile through the middle. Expanding this single-piece geometry around the central axis produces the full radial flow pump, featuring seven blades in total. The domain was meshed in TurboGrid using a structured grid totaling 63,308 elements.

Conclusion

Results include 3D contours of pressure, velocity, vapor phase volume fraction, liquid phase volume fraction gradient, and mass transfer rate gradient, along with 3D velocity vectors. The most critical results — vapor volume fraction and mass transfer rate contours — directly identify the specific locations within the pump where cavitation occurs, offering insight essential for evaluating cavitation risk and informing design changes aimed at mitigating pump damage and extending operational lifespan.