Gerotor Pump

Gerotor Pump CFD Simulation, ANSYS Fluent Training

Description

This project simulates a gerotor pump using ANSYS Fluent. A pump is a mechanical device that transfers liquid from one location to another, increasing fluid pressure to raise it to a higher elevation (via head increase) or drive it into another destination such as a tank. The pump draws mechanical energy from an external source, such as a motor, and transfers it to the fluid passing through, increasing the fluid's energy as it exits.

Pumps transfer this energy through either dynamic or displacement methods, dividing them into dynamic (non-positive displacement) pumps and positive displacement pumps — the latter further split into rotary types (gear, lobe, vane) and reciprocating types (piston, diaphragm). A gerotor pump is among the most common types used to increase a fluid's hydraulic power, moving liquid through the meshing action of two intermeshing gears rotating in the same direction, with one nested inside the other. As the gear teeth mesh together, fluid becomes trapped between them; as rotation separates the teeth again, this high-pressure fluid is carried along the ribs toward the outlet.

A gerotor pump is essentially an internal gear pump without the crescent-shaped divider — the single structural distinction between the two designs.

The geometry was designed in Design Modeler, representing the pump's internal space with two non-concentric, intermeshing gears. The domain was meshed in ANSYS Meshing using an unstructured grid totaling 51,182 cells.

Methodology

This project simulates water flow inside the gerotor pump, focusing on capturing the rotation of both gears and its effect on the surrounding flow. Since this rotation continuously alters the fluid domain, the computational mesh must deform correspondingly over time — requiring the dynamic mesh model, used whenever a moving boundary or deforming zone is present.

Since both gears rotate together, causing the mesh to deform over time, a Rigid Body was defined for each gear to represent its rotational motion, with a custom UDF governing this motion. The mesh region surrounding the gears was assigned the Deforming option to accommodate this continuous change. Given the inherently time-dependent nature of the resulting fluid behavior, the simulation was run using an unsteady (transient) solver.

Conclusion

Results include pressure and velocity contours along with velocity vectors, with corresponding animations capturing how these fields evolve as the gears rotate through their cycle. The results confirm that the gerotor pump operates correctly, effectively transferring fluid while raising its pressure: fluid becomes trapped in the space between the meshing gear teeth, then is pushed toward the outlet at elevated pressure — reproducing the gerotor pump's core operating principle as intended.