CFD studies on flow through screw compressor

Abstract

The twin-screw compressor is a positive displacement machine used for compressing gases to moderate pressures. It comprises of a pair of intermeshing rotors with helical grooves machined on them, contained in a casing which fits closely around them. The rotors and casing are separated by very small clearances. They may operate without internal lubrication, oil injected or with other fluids injected during the compression process. The rapid acceptance of screw compressors in various industries over the past thirty years is due to their relatively high rotational speeds compared to other types of positive displacement machines which make them compact, their ability to maintain high efficiencies over a wide range of operating pressures and flow rates and their long service life and high reliability. Every time generation of different profiles and evaluate performance of those profiles by experiments is very difficult and these are expensive and time taking process. By using CFD can find out performance of different profiles easier. The present work is aimed to create different screw compressor profiles in the GAMBIT. Generation of 3-D geometry and meshing of those profiles to evaluate performance of screw compressor in FLUENT has been done. Simulation of screw compressor working by using moving reference frame and dynamic mesh model in FLUENT is done. Internal leakage, which has a significant impact on the efficiency and performance, is an inherent problem in the design of a twin-screw compressor. The objective of this study is to understand the leakage flow mechanisms, and quantify the leaking rate through each leakage pathways in the screw compressor. The numerical analysis is conducted using Computational Fluid Dynamics (CFD) software commercially available, FLUENT. The Realizable k-e turbulence model is employed because it has shown substantial improvements over the standard k-e model where the flow features include strong streamline curvature, vortices, and rotation. Results show that the highest individual leakage occurs across the male and female rotor tip sealing lines, and the blowhole.