Investigation of the flow phenomena through a pump impeller in stall conditions with high-fidelity simulations
Centrifugal pumps account for a significant share of global industrial energy consumption. Optimizing the shape of all components is the main goal in the design process to improve operating efficiency and reduce environmental impact. However, centrifugal pumps often operate under off-design conditions, where the flow is characterized by large separations. The stall process of the impeller of a centrifugal pump is investigated in this work with high-fidelity simulations, considering all channels of the impeller instead of the reduced domain used in the literature under the assumption of a periodic flow behavior, in order to assess whether this assumption holds throughout the evolution of the stall process and whether the non-periodic behavior reported in the literature is phenomenological or related to the numerical setup. In particular, the goal is the description of the flow phenomena with different inlet flow rates, with a focus on the configuration of the vortices and the non-periodic behavior of the flow between the channels of the impeller. The setup of the simulations—e.g., the spatial accuracy of the meshes, the numerical schemes, and the formulation of the turbulence models—is assessed to avoid numerical errors that lead to poor accuracy and a deviation from the periodic behavior of the results. A large number of simulations are carried out, and the results are compared with experiments and other high-fidelity simulations available in the literature. The flow phenomena in the evolution of the stall process are progressive, where the increase in the dimensions of vortices is proportional to the decrease in the inlet flow rate. The stall is steady at each inlet flow rate, and the configuration of the vortices is periodic between all channels at the design and pre-stall conditions, and periodic between alternate stall and non-stall channels at the off-design conditions, confirming the periodic behavior assumed in most of the literature at the deep off-design conditions. All the non-periodic behavior of the flow can be ascribed to the spatial accuracy and turbulence model and decreases with high spatial accuracy, suggesting that it is more related to the numerical setup than to the flow phenomena. The proposed formulation of the turbulence model for high-fidelity simulations demonstrates the best compromise between accuracy and computational efficiency.