Three dimensional numerical analysis of screw compressor performance

Modern manufacturing methods enable screw compressors to be constructed to very close tolerances where full 3-D numerical calculation of the heat and fluid flow through them is then required to obtain the maximum possible improvements in their design. An independent stand-alone interface program has been developed by the authors in order to generate a numerical grid for this purpose. The interface employs a procedure to produce rotor profiles and an analytical transfinite interpolation method with adaptive meshing to obtain a fully structured 3-D numerical mesh, which is directly transferable to a CFD code. This was required to overcome problems associated with moving, stretching and sliding rotor domains and with robust calculations in domains with significantly different geometry ranges. Some changes had to be made within the solver functions both to enable calculations and to make them faster. These include a means to maintain constant pressures at the inlet and outlet ports and consideration of two-phase flow resulting from oil injection in the working chamber. Modifications implemented to the CFD procedure improved solutions in complex domains with strong pressure gradients. The pre-processor code and calculating method have been tested on a commercial CFD solver to obtain flow simulations and integral parameter calculations. The results of calculations on an oil injected screw compressor are presented in this paper and compared with experimental results.