CFD Simulation of a Dry Scroll Vacuum Pump Including Leakage Flows

One challenge for the numerical simulation of a dry scroll vacuum pump is the discretization of the chamber volume, which changes with time. In addition, the flow characteristics are very complex including the leakage flow caused by radial and axial gaps between the rotors and the housing. For engineers and designers it is imperative to understand the influence of such leakage flows on the efficiency of the dry scroll vacuum pump. This paper describes the workflow for Computational Fluid Dynamics (CFD) of a dry scroll vacuum pump and shows some preliminary results. The computational grids for the time dependent flow volume are generated by the grid generator TwinMesh. The meshing software generates and optimises all necessary grids for each time step prior to the actual simulation and calculates the mesh quality to assure high quality numerical results. Furthermore, the grid generation accurately considers axial gaps. The transient numerical simulations are performed by the commercial CFD software code ANSYS CFX, which is able to handle complex flow characteristics. The simulations consider compressibility, turbulence, and heat transfer effects using ideal gas properties for the fluid. The pressure ratio between inlet and outlet is varied as well as the gap size. The results are compared with analytical methods. This paper shows time dependent information such as pressure, velocity, and temperature for specific locations in the chamber volume and also integral values such as power, torque, and mass flow. Finally, cross-sectional views are presented for different positions and time steps.