Cfd Analysis of Screw Compressor Performance

Modern manufacturing methods enable screw compressors to be constructed to such close tolerances that full 3-D numerical calculation of the heat and fluid flow through them is required to obtain the maximum possible improvements in their design. An independent stand-alone CAD-CFD interface program has therefore been developed by the authors in order to generate a numerical grid for this purpose. Modifications implemented to the CFD procedure improved solutions in complex domains with strong pressure gradients. The interface employs a rack-generation procedure to produce rotor profiles and an analytical transfinite interpolation method to obtain a fully structured 3-D numerical mesh, which is directly transferable to a CFD code. Some additional features, which include an adaptive meshing procedure, mesh orthogonalization and smoothing, are employed to generate a numerical mesh which can take advantage of the techniques used in recent finite volume numerical method solvers. These were required to overcome problems associated with i) rotor domains which stretch and slide relative to each other and along the housing ii) robust calculations in domains with significantly different geometry ranges. iii) a grid moving technique with a constant number of vertices. Some changes had to be made within the solver to increase the speed of calculation. 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. 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. Good agreement was obtained between them.