Multiphase Flow Analysis in an Oil-injected Twin Screw Compressor

Oil injected twin screw compressors are widely used in industry for gas compression because of their high volumetric efficiency and reliability. The injected oil has a significant influence on the performance of these compressors. Only an optimum quantity of oil supply would give best performance at a specified operating condition. Therefore, it is essential to determine the distribution of oil in the working chamber and thereby the compressor’s performance. Using Computational Fluid Dynamics (CFD) to solve two-phase flow in deforming domains is numerically challenging due to the complex interactions between air and oil in rotating machines. In this paper, two Eulerian-Eulerian multiphase models have been investigated. Namely, inhomogeneous and homogeneous model with free surface modelling have been investigated for their stability, oil-air distribution and accuracy of compressor performance results. Deforming rotor mesh needed for the simulation is generated by SCORG TM grid generator while two-phase transient flow is solved with ANSYS CFX solver. Results obtained from the simulation have been compared with the measured data of mass flow rate of gas, indicated power and temperatures. Inhomogeneous model predicts data closer to the experimental results and an expected distribution of oil in the rotor tip clearances. For a high mesh deformation of a working domain in twin screw compressor, the inhomogeneous approach also provides better stability of the solver, but this is at an added cost of calculation time. In future, better initialisation and solver parameters with oil droplet characterisation will be required to further improve the model.