Numerical Investigation of the Minimum Gap Impact on the Screw Compressor Efficiency

Abstract

The screw compressor is a positive displacement machine, with two rotors - driver and driven. In this paper, the influence of minimum gap, between the rotors of an oil injection screw compressor, on the efficiency was investigated. Two cases were analysed, in which the minimum gap ranged from 40 to 60μm, respectively 20 to 40μm. The geometrical model, the physical properties and the initial values represent the input data for the used thermodynamic model. Starting from the 3D CAD model, the computational domain for the stator part was defined, which is composed of three subdomains: suction side, oil inlet and pressure side. The grids for the stator were generated with Ansys Meshing, whereas the meshes for the rotor subdomains were made using the TwinMesh software. In the end, smoothing functions were used to increase the mesh quality. To simulate the flow through the screw compressor, the commercial software of CFD ANSYS CFX was used, employing the SST turbulence model. In the analysis the rotational speed was 6000rpm, with a suction pressure of 2bar and a discharge of 10bar. Using the “opening” type limit conditions with the required pressure, both the air flow variation and the oil flow variation were determined.