Abstract

Rotary compressors such as screw compressors, roots blowers, and turbo compressors are used in industry to compress process gases, or as vacuum or backing pumps to evacuate vessels. Gas is sucked in at low-pressure side, transported and compressed by size-changing chambers (PD machines) or energy transmission from rotor to fluid (turbo machinery), and released at high-pressure side. In expanders or turbines, flow direction is from high to low pressure side to gain energy from pressurized gases. The 3D CFD simulation of such compressors/expanders is complex and time-consuming due to its transient nature and fine meshes to ensure a proper representation of radial and axial gaps in the range of some microns with machine dimensions up to meters. Due to this complexity, 3D CFD simulation should focus on the component, i.e. the compressor, and the attached overall system with vessels, valves, pipes, and consumers should be simulated in a 1D network or system simulation. Due to oscillations in the gas flow and interaction with the connected system a transient coupling is necessary. In this paper we show a 3D CFD simulation of a screw compressor using ANSYS CFX in a co-simulation with the 1D Flownex simulation environment of a network modelling the pressurized gas distribution. Whereas the 3D solver works on meshes with up to several million nodes in parallel on HPC systems, the 1D solver typically works serially on several thousand nodes that discretize the flow direction. The transient coupling is based on the exchange of variables at the boundaries of each simulation for every time step allowing for detailed analysis. The impact of the acoustic propagation of pressure fluctuations and the pulsating fluid flow provided by the compressor on the distribution system, and in return the effects of the system response on the compressor are evaluated. Furthermore transient scenarios such as start-up procedures or component failure will be shown.

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