Numerical methodology for the CFD simulation of diaphragm volumetric pumps

Abstract

This paper presents the unsteady numerical methodology for the CFD simulation of Air-Operated Diaphragm Pumps. The model reproduces the unsteady displacement of the diaphragm using dynamic mesh techniques and fully resolves the Fluid Structure Interaction (FSI) responsible for the motion of the check valves. The governing parameters have been modified with User Defined Functions (UDFs), using an implicit scheme for the grid motion that guarantees the stability and realizability of the two-dimensional model adopted.The analysis of the instantaneous delivered flow rate, as a function of the discharged outlet pressure, has provided interesting and useful information for the future design of new prototypes. The comparison between numerical results and the experimental performance curves has confirmed the accuracy of the model and the correct mesh selection in the small gaps and passages of the pump internal geometry.The leakage flows, especially in the exhausting valve during the forward stroke, and the ball tapping responsible for instabilities and high-frequency noise during oscillations of the valves has been accurately simulated. At high-delivered pressures, it has been observed a characteristic ripple in the instantaneous flow rate during the deceleration of the diaphragm towards its top-dead-center, associated to a partial re-opening of the exhausting valve.A closer look to the dynamics of the balls has revealed a strong coupling between inlet and outlet check valves. In addition, despite of the remarkable level of accuracy (less than 9% of deviation), the recirculating cells found in the flow fields inside the pump suggest the convenience of the development of a full-unsteady 3D model in the near future.