Three-dimensional (3D) unsteady Reynolds-averaged Navier–Stokes (URANS) flow simulations are conducted to investigate the highly unsteady flow field at part load operation of a centrifugal pump. By the availability of unsteady flow field measurement data in the impeller wake region, a thorough validation of the simulation method is performed. Grid independence of the results is ensured. Unsteady characteristics in terms of head and shaft power as well as transient blade loads are evaluated to assess the unsteady pump performance. Significant mis-loading of the blading is revealed when one blade passes the volute tongue and associated with the strong unsteady and 3D flow field in the impeller-volute tongue region. Negative radial velocity in the tongue region is the origin of a vortex at the blade pressure side and a subsequent pressure drop that leads to even temporally negative blade loading. The results provide a detailed insight in the complex part load flow field that might be utilized for an improved pump design. As a valuable secondary outcome, a comparison of results obtained by two widely used computational fluid dynamics (CFD) codes for pump flow simulation is provided, i.e., the commercial code ansyscfx and the branch foam-extend of the open source software openfoam. It is found that the results of both methods in terms of unsteady characteristics as well as local ensemble-averaged velocity field are consistent.
The accuracy of linear eddy-viscosity URANS turbulence modelling is assessed for offdesign operation of a single stage radial centrifugal pump. The open source software OpenFOAM is utilized. Hot wire probes have been utilized for measurement of spatially and temporally resolved validation data at the impeller discharge of the air-operated pump. The ensemble-averaged mean flow angle is in qualitatively good agreement to data for the entire operation range, while minor deviations occur close to the volute tongue due to impeller-volute interaction. Turbulence statistics from the simulation are compared to ensemble-averaged velocity RMS from measurements. RMS distribution is also qualitatively well reproduced for near-design and overload operation. A more pronounced RMS mis-prediction occurs in part load in the region of high impeller-volute tongue interaction and reveals limitations of turbulence modelling in highly unsteady flow regions of centrifugal pumps.
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