Boundary adaptation in grid generation for CFD analysis of screw compressors

This paper describes some aspects of an advanced grid generation method used, with Computational Fluid Dynamics (CFD) procedures, to model three-dimensional flow through screw compressors. The increased accuracy of the flow predictions thus derived, enable such machines to be designed with improved performance and for lower development costs. To achieve this, a wholly original boundary adaptation procedure has been developed, in order to allow for convenient mapping of the internal grid points of a screw compressor, which is sufficiently flexible to fit any arbitrary rotor profile. The procedure includes a practical transformation method, which adapts the computationally transformed region to produce a regular boundary distribution on the mesh boundaries. It also allows for subsequent generation of an algebraic grid, which enables the three-dimensional domain of a screw compressor to be mapped regularly even in regions where the flow patterns are complex and the geometrical aspect ratio is high. This procedure enables more efficient use of a CFD solver for the estimation of the flow parameters within both oil free and oil injected screw compressors, with either ideal fluids or real fluids, with or without change of phase