Understanding loss generation mechanisms in a centrifugal pump using large eddy simulation

Water pumps are amongst the most frequently used turbomachines, which consume about 9% of the global energy production. This paper provides insight on the loss generation mechanisms in inline centrifugal pumps operating under realistic conditions through a detailed analysis based on large eddy simulation (LES). The equations for the resolved, sub-grid and wall entropy generation terms are derived using the LES filtering and Smagorinsky-Lilly formalism. Specific exergy is calculated at the grid points. Entropy generation and exergy transfer within the flow domain are visualised to highlight the loss generation mechanisms within the pump. Results show that there is a strong component interaction. The double-bended inlet pipe initiates Dean-vortices at the eye of the impeller. This asymmetric inflow coupled with the disturbances at the cut-off cause a non-uniform flow through the blade passages. Other drivers of the asymmetrical loading of the blade passages are high leakage and unsteady and asymmetrical mass and exergy transfer between the dead zone. The paper also investigates the effect of the grid resolution on the first and second order statistics of the flow field and its turbulent characteristics. A thorough evaluation of the discretisation error is presented to provide a measure for the required grid density and demonstrate the extent and impact of the temporal and spatial discretisation error in centrifugal turbomachinery.