Highly Deforming Computational Meshes for CFD Analysis of Twin-Screw Positive Displacement Machines

Commercial flow solvers can be used to obtain flow solutions in applications with deforming domains, but, in general, are not suitable for screw machine flow calculations. This is due to the large magnitude of deformation of the domain and the geometrical complexity of helical rotors. In this chapter, the governing equations for deforming domains and three methods of obtaining mesh movement, commonly used by FVM solvers, have been analysed. A comparative study of customised methods of grid generation for screw machines, using algebraic and differential approaches, is shown to help in the selection of techniques that can improve grid quality, robustness and speed of grid generation. The analysis of an oil-injected twin-screw compressor is included as a test case to demonstrate the application of SCORG, a deforming grid generator, as a means of predicting performance.