However, in a vane pump, there is normally direct contact between the vanes and the stator and a leakage could occur only in the case of detachment of the vane during the transition between the suction and delivery volumes. The code also allows the consideration of a constant gap on the vane tip. Since the main leakage passageway was due to the axial clearance between the cover and the rotor, a disc of cells made up of three layers (not shown in Figure 1b) was added. In order to adjust the grid to the volume variation, the cells were shortened or stretched radially. Each chamber was discretized in 720 cells in the tangential direction, 32 in the radial direction, and 16 axially. In the variable chambers, the cells were anchored to the vanes and to the outer diameter of the rotor, while sliding with respect to the stator.

A specific template for vane pumps was used. The moving chambers are connected to the fixed volumes through Mismatched Grid Interfaces. In the CFD environment, the mass and momentum equations are solved by discretizing the computational domain with the finite volume method. The commercial software PumpLinx was used for performing the 3D simulations. Moreover, the filling could be improved by increasing the number of chambers, and by reducing the diameter of the rotor, even only locally. Opposite behaviors were found in the case of pumps with small diameters and high thicknesses.

It was found that a pump with a low ratio between the axial thickness and the diameter has a higher volumetric efficiency if the chambers are fed from one side only. At first, a model of a reference pump has been created and validated with different configurations of the suction flow area, then a simplified model has been used for assessing the influence of the geometry of the rotating assembly.

In this paper, the influence of different geometric parameters on the filling of a vane pump has been investigated through the commercial software PumpLinx ®. The prediction of the limit speed and of the maximum flow rate delivered by a pump can be obtained only through Computational Fluid Dynamics (CFD) simulations, since the shape, the orientation, and the movement of the chambers with respect to the inlet volume must be considered, along with the non-uniform distribution of the gaseous phase, due to the dissolved air release. In positive displacement pumps, the main volumetric loss at high speed is due to the incomplete filling of the variable volume chambers.

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