engleski

CFD simulation of off-design operating points of a centrifugal compressor

CFD simulations of turbomachinery are now a part of the standard approach in the design process. However, CFD as an investigation tool in the later stages of the design process, namely to investigate off–design operating points and fluid flow instabilities are rarely used in practice. The main objective of this work is to investigate the applicability of CFD software, eg. open–source library foam-extend to predict the flow field corresponding to off-design operating conditions of a centrifugal compressor. Since a full rotor geometry is challenging to model due to the size of the computational mesh, we decided to investigate performing the simulations on a single blade passage using cyclic boundary conditions for non–conforming meshes (Generalised Grid Interface – GGI). The mesh is block–structured, created in Pointwise with 7.2 million cells. A Multiple Reference Frame approach is used to model the rotation, which means that the obtained flow field corresponds to a single rotor position. Start–up of the simulation if very sensitive due to the extreme operating conditions of the nominal operating–point, and it is necessary to introduce the boundary conditions gradually. Thus, the total pressure ratios and MRF angular velocity are increased progressively to prevent the simulation from crashing due to local extreme velocities and pressure values. To validate the simulation approach, a comparison is made to experimental and numerical data provided by Dewar and Tiainen [8]. The final objective is to create a compressor map with the established flow field features corresponding to different operating points, and some close surge and choke conditions.

CFD ; OpenFOAM ; foam-extend ; turbomachinery ; centrifugal compressor

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