The model accounts for radial and axial clearances between rotors and stator, where rotors and stator are connected with interfaces. A specific meshing method is used to model the size-changing working chambers between rotors and casing, where only hexahedral cells are used and mesh topology is constant. To enhance the performance of the compressor, discharged air from the first stage is cooled down before entering the second stage. The total pressure ratio of the two stages combined is up to 10:1. Each stage features different rotor profiles, where the first stage has a 4-6, the second stage a 5-7 lobe combination. The two stages are gear driven by the main shaft at rotational speeds between 11 rev/min. It is a dry running two stage twin screw compressor running with air at a rated power range between 160 and 250 kW. This paper presents the methodology of creating the numerical model for a sample screw compressor provided by Sullair for research purposes. The desired simulation approach should be able to deliver sufficient accuracy at a feasible effort in terms of computational time and manpower to create the numerical model. As CFD methods evolve in general, but also for the application of PD machines in particular, the numerical model can replace a prototype during early stages of the product development. Compressible fluids, real-gas properties and leakage flows with trans- or supersonic characteristics are phenomena which have to be accounted for in order to properly model the behavior of the machine. The working chamber and thus the discretized flow domain of PD machines are changing in time, characterized by complex thermodynamics. In the past years, it has proven to become more and more applicable for modeling the flow physics inside positive displacement (PD) machines. Computational Fluid Dynamics (CFD) is a common and validated simulation method in research and industry for the analysis of fluid systems.

Pro ii simulation two compressor lab