Fluids are pumped by means of external gear pumps, which are positive displacement pumps that trap and transfer fluids between spinning gears. They are made up of two gears, often spur gears, which mesh and revolve within a pump casing. One gear is powered by a motor or another source of power, while the other drives by meshing motion. Figure 1 depicts the working mechanism of an external gear pump. External gear pumps have wide applications in different industrial sectors, such as hydraulic systems, lubrication systems, fuel transfer, and chemical processing. They are highly regarded for their exceptional efficiency, unwavering reliability, and remarkable capability to handle various viscosities and pressures. This project requires simulating an external gear pump in 2D mode using the ANSYS Fluent software and the dynamic mesh module. In addition, a user-defined function has been compiled to consider the rotational motion of the gears, with one rotating clockwise while the other rotates in the opposite direction.

• Refererence [1]: Martínez, Javier. “Mesh handling for the CFD simulation of external gear pumps.” Positive displacement machines. Academic Press, 2019. 345-368.

Figure 1- Fluid transfer mechanism through a gear pump [1]

Simulation Process

Firstly, the geometry is designed using Spaceclaim software. This step requires a careful consideration of kinematics in order to prevent collisions. A schematic of the present model is shown in Figure 2.

Figure 2- Schematic of the designed computational domain

Next, an unstructured grid is generated using ANSYS Meshing software. Due to small regions between two gears, proximity is utilized to fill the gaps carefully. In conclusion, 172324 triangular elements are produced with an acceptable mesh quality.

Although the flow regime is expected to remain laminar, k-w SST turbulence model is used to avoid any imminent errors. A UDF is written to apply the revolving motion of the gears around their centers of gravity. Besides, the gears are assumed to be rigid bodies. Moreover, Smoothing and Remeshing techniques of Dynamic Mesh are activated to control the reshaping of elements during the movement.

Post-processing

Through in-depth pressure and velocity distributions, the external gear pump’s computational fluid dynamics (CFD) study shows fundamental flow features. The basic working concept of positive displacement pumps is shown by the dynamic mesh simulation, in which the pressure field fluctuates between -15 kPa in the suction zone and +25 kPa at the discharge region. The transient analysis reveals how the counter-rotating spur gears produce a pressure difference that accelerates fluid flow by causing a cyclical swings in the inter-tooth volume. understanding gear pump performance parameters, such as volumetric efficiency and pressure pulsation characteristics, requires a knowledge of this pressure-driven flow mechanism. Through cavitation prevention design considerations, the ANSYS Fluent findings clearly show how low-pressure zones occur during tooth separation, facilitating fluid intake.

Figure 3- distribution of a) pressure b) velocity around the gears

The velocity profiles and flow field analysis reveal complicated fluid dynamics patterns within the gear mesh region, with velocities ranging from near-stagnation points to peak values of around 12 m/s in the tooth gaps. In fluid entrainment and transport, where fluid particles accelerate quickly through the meshing zone, the streamline visualization emphasizes the essential function of gear tooth geometry. As the teeth mesh, the confined fluid volume is compressed, increasing the discharge pressure and velocity. This is demonstrated by the dynamic mesh simulation, which records the temporal evolution of the pressure and velocity fields. This research offers useful information for optimizing gear pump design, especially for applications that call for accurate flow control and handling of different fluid viscosities. Despite the primarily laminar flow regime, the results confirm that the k-ω SST turbulence model is successful in capturing the intricate flow features.