Computational fluid dynamics simulation study of gas flow in dry scroll vacuum pump

Based on CFD method and dynamics mesh method, the transient flow simulation model of dry scroll vacuum pump was established. Numerical calculation was carried out under three kinds of typical working conditions of viscous flow state including under-compression, slightly over-compression and over-compression. Simulation results are in line with the results of experiment or theoretical calculation on the whole. The maximum error of pumping speed between the simulation and the experiment is about 30%, and the minimum is close to 10%. The predicted compression power accords with the theoretical prediction of approximate polytropic process. The simulation pressure inside the pump also has a consistent change process with experimental results. The contrast and analysis of the simulation model and the physical experiments suggest that the further correctly modified geometric parameters and boundary conditions according to practical situations can significantly improve the accuracy of the numerical calculation. Further analysis of the main flow phenomena and characteristics of scroll compression chamber at the discharge side during the discharge process confirms that under-compression and over-compression lead to the large variation of gas pressure and dramatic fluctuation of compression torque.