Gerotor Pump: Cavitation, UDF

Numerical Investigation of Cavitation Phenomena in a 2D Gerotor Pump Using ANSYS Fluent

Description

Gerotor pumps play a crucial role in fluid transfer applications across modern hydraulic systems, but they frequently face challenges related to cavitation, which can significantly affect both performance and long-term durability. This study presents a detailed numerical investigation of cavitation behavior within a gerotor pump using a two-dimensional CFD model in ANSYS Fluent, aiming to understand and characterize how and where cavitation develops during pump operation.

The 2D geometry was built in Design Modeler, accurately capturing the complex profiles of both the inner and outer rotors characteristic of gerotor pump design. The domain was meshed in ANSYS Meshing, generating approximately 50,000 elements — a mesh density chosen to balance computational efficiency against solution accuracy, particularly given the added demands of dynamic mesh operations required to capture rotor motion.

Methodology

The simulation used a pressure-based transient solver, with the SIMPLE algorithm handling pressure-velocity coupling. First-order upwind discretization was applied to momentum, volume fraction, and turbulence equations to maintain solution stability and convergence.

Cavitation was captured using the Mixture multiphase model, with water as the primary liquid phase and water vapor as the secondary phase, representing the phase change driving cavitation formation. Turbulence was resolved using the RNG k-epsilon model, selected for its robust performance in rotating machinery applications.

Rotor motion was implemented through dynamic mesh capabilities driven by custom UDFs, controlling the inner rotor at 30 rad/s and the outer rotor at 24 rad/s. Boundary conditions included a pressure inlet at 0 Pa gauge pressure and a pressure outlet, with all solid boundaries treated as standard no-slip walls.

Conclusion

The simulation results provide comprehensive insight into the pump's operation and cavitation behavior. Pressure contours reveal regions of potential cavitation formation, concentrated specifically in low-pressure zones, while velocity contours illustrate the complex flow patterns within the pump, highlighting areas of high velocity and potential flow separation. Water volume fraction visualizations help pinpoint the specific zones where cavitation actually occurs during operation, with the accompanying animation capturing how the flow field and cavitation development evolve dynamically throughout the rotation cycle.

The interaction between the rotating rotors and the fluid produces clear, identifiable patterns of pressure fluctuation and vapor formation, confirming that the numerical setup successfully captures the cavitation phenomena occurring within the gerotor pump. These findings offer valuable insight into how cavitation may affect pump performance and efficiency, and identify the critical regions where design modifications could help minimize cavitation effects — providing a solid foundation for future gerotor pump design improvement and optimization studies.