Performance Optimization of Screw Compressors Based on Numerical Investigation of the Flow Behavior Based on Different Grid Generation Approach

In the field of screw compressors, although the basic operation of flow systems is well known and the analytical methods for their performance prediction are well established, only few attempts of investigating the flow by means of CFD can be identified in the available literature. In this paper, two important aspects of numerical investigation of the flow behavior are presented. Firstly, methodology for grid generation of constant pitch twin screw machines is available through SCORG© but it is currently not suitable for different topologies like that of a single screw or variable pitch rotors. Hence a currently available technology of grid remeshing has been used to demonstrate the CFD simulation of an adiabatic compression-expansion process in a reciprocating piston cylinder arrangement. This simulation gives a basis for application of this grid generation technique for screw compressors. The methodology tested for this paper uses a technique called key-frame re-meshing in order to supply pre-generated grids to the CFD solver as the solution progresses. It was concluded that customized tools for generation of CFD grids for such complex screw machines still remain to be developed. Secondly, it is intended in this paper to put an emphasis on the current features and potential for development of SCORG© a customized grid generator, to establish CFD as permanent tool for compressor design and optimization in the New Product Development process. The definition of an optimum meshing procedure and, subsequently, of appropriate boundary conditions, allowed the successful setup of flow simulations in an oil-free screw compressor and the prediction of the compressor performance, with a good degree of confidence. The flow analysis included both qualitative and quantitative evaluations of parameters like the variation of the pressure and temperature in the discharge chamber, torque, power, and entropy variation. This detailed analysis allowed for design improvements of the discharge chamber to be implemented and “virtually” tested in order to determine an optimized compressor geometry, which will be subsequently incorporated in the actual modular casing of the compressor.