Performance Optimization of Screw Compressors Based on Numerical Investigation of the Flow Behavior in the Discharge Chamber

摘要

In the field of screw compressors, although the basic operation of such flow systems is well known and thernanalytical methods for their performance prediction are well established, only few attempts of investigating the flowrnin screw compressors by means of CFD can be identified in the available literature. The present paper aims atrncontributing to this field by establishing CFD as permanent tool for compressor design and optimization during thernnew product development process at a screw compressor manufacturer.rnThe major challenges during this process related to the implementation of a valid meshing technique, as this is a farrnmore unconventional process in the case of screw compressors than any other meshing techniques available withinrnthe commercial solvers, due to the very tight interlobe clearances. The definition of an optimum meshing procedurernand, subsequently, of appropriate boundary conditions, allowed the successful setup of flow simulations in an oilfreernscrew compressor and the prediction of the compressor performance, with a good degree of confidence.rnWithin the scope of the present paper, the CFD analysis focused on two main objectives. Firstly, a baseline modelrnfor the optimization exercise was determined: the discharge chamber (discharge port, pipe and flanges) of thernmodular casing of the single-wall/ rolling-element bearing/ compressor, characterized by a rotor diameter of 127rnmm. Secondly, the performance of the baseline was assessed against that of several new designs which aimed atrnimproving the gas flow in the discharge chamber.rnAt the comparison stage, the correct definition of accurate performance indicators was very important, as thesernindicators had to capture the overall flow improvements achieved by the new designs. The flow analysis includedrnboth qualitative and quantitative evaluations of parameters like the variation of the pressure and temperature in therndischarge chamber, torque, power, and entropy variation. This detailed analysis allowed for design improvements ofrnthe discharge chamber to be implemented and “virtually” tested in order to determine an optimized compressorrngeometry, which will be subsequently incorporated in the actual modular casing of the compressor.