External Gear Pump CFD Simulation, Dynamic Mesh

Description

This project is related to the External Gear Pump numerical simulation using ANSYS Fluent software. A pump is a mechanical device for moving and transferring all liquids from one place to another. In this way, by increasing the pressure, pumps cause liquids to move to a higher height (by increasing the head) and even lower (such as tanks).

This product is the fifth chapter of the Dynamic Mesh Training Course.

In fact, the pump takes mechanical energy from an external source, such as a motor, and transfers it to the fluid passing through it. As a result, the energy of the fluid increases after leaving the pump.

The energy transfer to the pump fluid is done in two dynamic and displacement methods. Therefore, pumps are divided into two categories: positive displacement pumps and dynamic or non-positive displacement pumps. Positive displacement pumps are divided into two groups: rotary (such as gear, lobe, and vane) and reciprocating (piston and diaphragm).

A gear pump is one of the most common pumps to increase the hydraulic power of a fluid. Gear pumps move liquids using gears. These gear pumps are made of two types of internal and external gears.

External gear pumps consist of two gears that rotate in opposite directions. When two gears make contact with their teeth, fluid is trapped. Now, when the teeth are separated from each other due to rotation, high-pressure fluid is rotated through the ribs to the outlet.

In this project, we simulated the water flow inside an external gear pump.

We aim to model the rotation of two gears inside the pump. The gears’ rotation changes the fluid’s behavior in the pump momentarily. So, the mesh of the computing domain deforms over time.

We modeled the geometry of the project using Design Modeler software. The geometry is related to an external gear pump. The computational domain includes the internal space of the pump with two superimposed gears. Then we meshed the model with ANSYS Meshing software. The model mesh is unstructured, and the number of cells equals 9,254.

External Gear Pump Methodology

The Dynamic Mesh Model is used in this simulation. We generally use a dynamic mesh whenever we have a moving boundary or a deforming zone.

Here, two gears are rotating in opposite directions. So this causes the mesh to deform over time. Therefore, we define a Rigid Body to define the rotational motion of the gears. We use a user-defined function (UDF) to define the motion of the rigid body.

According to the rotational motion of the gears as a rigid body, the mesh zone around the gears is deformed. So, for this zone, we use the Deforming option.

Due to the nature of this modeling, fluid behavior is time-dependent. Hence, we use the unsteady (Transient) solver.

Conclusion

After the solution, we obtained pressure and velocity contours. Because the gears rotate over time, we obtained the animation of the velocity and pressure contours.

The results show that this gear pump is working correctly. This pump can transfer the fluid well and increase the fluid’s pressure. The fluid is trapped in the space between the gears in contact. Then this fluid is pushed towards the outlet with high pressure.