Grid Generation for Screw Compressors with Variable Geometry Rotors

An algebraic grid generation algorithm is presented in this paper which enables the per- formance of twin screw compressors with variable rotor geometry to be predicted, by means of Computational Fluid Dynamics (CFD). It is based on a method, previously developed by the authors, for compressors with standard uniform pitch rotors and con- stant cross-section profile, which has now been extended to include rotors with variable pitch and/or variable profile. By its use with the commercial CFD solver ANSYS CFX, it has been possible to obtain performance predictions for three variants of an oil-free 3/5 screw compressor, namely uniform helical rotors, variable pitch rotors and variable profile rotors. The variable pitch and variable profile rotors achieve steeper internal pres- sure rise and a larger discharge area for the same pressure ratio. Variable pitch rotors also showed lower leakage rates due to reduced sealing line length in the high pressure domain. This grid generating procedure advances the ability to evaluate both existing and novel compressor configurations.