Computational Fluid Dynamics (CFD) simulations are a valuable tool for hydrodynamic pump flow analyses. Recently, emphasis has been placed on the analyses of all pump modes such as turbine mode, pump mode, dissipative modes etc. Some regimes are very difficult to simulate numerically, especially transition states. These regimes must be analysed using multiple modelling approaches, considering different levels of model complexity. The CFD simulations are very useful for predicting emergency scenarios such as a pump failure, counter-pressure from the pipeline system, reverse flow, water-hammer events, etc. The future validation of simulations by experimental research is self-evident. The pump test bench is currently being prepared, for this purpose, as shown in this article. The pump test bench consists of two identical centrifugal pumps: a measured pump and feed or auxiliary (it depends on the regime in the four-quadrant characteristic) pump. These pumps, together with the pipeline system including a bypass, make it possible to measure the complete (four-quadrant) pump performance characteristics. This paper is focused on numerical simulations of the dissipative operations and non-standard pump regimes with emphasis on the analysis of the transition state between the first and second quadrant and between the second and third quadrant. The article describes and presents a comparison of different modelling approaches from the view of varying model geometry complexity. The simulation results are compared based on the performance characteristics, which could represent future test bench limits. The flow behaviour in the pump and piping system is also visualized, and it is a valuable result that can be considered in the future experiment.
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