Three-dimensional numerical simulation and experimental validation of flows in working chambers and inlet/outlet pockets of Roots pump

In this study, two cases of three-dimensional computational fluid dynamics (CFD) were established to simulate the flow in Roots pumps, using the dynamic mesh method. The difference between these two cases is in the size of pipes which represents the valves at the inlet/outlet piping. A physical Roots pump was manufactured to allow testing of the pressure distribution and the mass flow rate in order to validate the CFD models. The results showed that both simulated models were fairly acceptable in terms of the mass flow rate, but the results from the case with narrow pipes agreed much better with the experimental results in terms of pressure distribution. The simulated velocity fields during the working cycle showed the presence of vortexes at both the inlet and outlet pockets. The vortexes at the inlet pocket were close to the rotor, but those at the outlet pocket were around the cylinder wall. Furthermore, a two-dimensional model was established to determine whether this simpler model can predict performance accurately. The results showed that the 2-D model gave satisfy accurate results for in terms of mass flow and pressure distribution, but failed to predict the velocity field accurately.