Moving Mesh (Mesh Motion): Twin Screw Pump

Twin Screw Pump — ANSYS Fluent CFD Simulation

This project analyzes the operation of a twin-screw pump using ANSYS Fluent. A twin-screw pump is a positive displacement device, transferring a fixed volume of fluid per cycle based on the rotational speed and pitch of its screws. As the two screws turn, they form enclosed chambers that move along the axial direction, creating a vacuum at the inlet and positive pressure at the outlet. This double-chamber arrangement allows the pump to handle fluids of both high and low viscosity with minimal pulsation.

More specifically, the pump consists of two counter-rotating screw rotors that turn toward each other, trapping fluid in the space between their threads. As the screws rotate, this trapped volume progressively shrinks, compressing the fluid and driving it toward the outlet.

In this study, the pump is used to handle a highly viscous fluid—glycerin. The rotation of the screws draws glycerin into the domain, increases its pressure, and pushes it toward the outlet.

The geometry was designed in SolidWorks and refined in ANSYS Design Modeler, consisting of two rotating zones (the screw rotors) and one stationary zone (the pump housing). The model was meshed in ANSYS Meshing using an unstructured mesh, totaling 1,184,161 cells.

Methodology

Rather than applying rotation directly to the rotor geometry, the rotational motion is imposed on the surrounding fluid through a dedicated computational zone defined in the cell zone conditions. This is achieved using the Mesh Motion method, with a rotational velocity of 3 rad/s. Pressure boundary conditions are applied at the inlet and outlet, since fluid movement through the pump is driven entirely by pressure differences rather than forced flow.

Results

The simulation produces 2D and 3D contours of velocity and pressure, along with streamlines around the rotors. The results show that fluid motion through the pump is governed by pressure gradients: rotor rotation generates suction at the inlet and pushes the fluid toward the outlet, with the streamlines clearly illustrating the rotational flow pattern inside the pump.