With environmental awareness growing in many countries, governments are taking measures to reduce mortality of migrating fish in pumping stations. Manufacturers seek to develop pumps that are less damaging to fish and still provide good hydraulic performance, but little is known about the implications design modifications may have on internal flow characteristics and overall hydraulic performance. In this paper, an integrated design method is proposed that combines a validated blade strike model for fish damage and a computational fluid dynamics method to assess the pump performance. A redesign of an existing, conventional, axial flow pump is presented as an example in this paper. It shows how the design of the impeller blades was modified stepwise in order to reduce fish mortality while its hydraulic performance was monitored. Computational fluid dynamics analysis of the flow near the hub of the highly skewed blades indicated that unconventional design modifications were required to ensure optimum flow behavior. In the final fish-friendly design, the risk of fish mortality has reduced considerably while the hydraulic performance of the pump is still acceptable for practical application.

In order to improve the hydraulic efficiency and internal flow pattern of a multi-stage pump under multiple flow conditions, an intelligent optimization design was proposed for its hydraulic components. Sensitivity analysis was used to select the key parameters influencing the hydraulic efficiency of a multi-stage pump. The optimal Latin hypercube sampling and non-dominated sorting genetic algorithm Ⅱ were employed to build a multi-objective optimization system. Moreover, a radial basis function neural network was adopted as the surrogate model of hydraulic efficiency. The research results showed that the impeller outlet width, impeller blade wrap angle, impeller outlet blade angle, and diffuser inlet width were the key factors affecting the hydraulic efficiency. The efficiency of the optimized model increased by 4.35% under the design condition and the matching of the internal flow between the optimized impeller and diffuser was significantly enhanced under the nominal condition. The improved flow pattern could be clearly observed in the flow passage of both the pump impeller and the diffuser. After optimization, the wear performance of the model was also improved compared to the original design. The wear area decreased in size and was distributed more evenly, resulting in a noticeable decrease in the maximum amount of wear.

Complex flow patterns in a large vertical centrifugal pump (LVCP) when operating in the hump region under cavitation conditions should deserve more attention. This research investigates the interaction between cavitation and vortices in LVCP from the perspective of rigid vortex transport characteristics and modal decomposition. The hump characteristics of LVCP are more pronounced under cavitation. The backflow vortex cavitation at the impeller inlet and the leading edge cavitation of the diffuser vanes can be found under part-load conditions. Rigid vortex analysis reveals the low pressure backflow vortices are generated between the impeller inlet and the inlet pipe. The fusion of leading edge separation vortices with pressure surface separation vortices and shedding high pressure trailing edge separation vortices in the diffuser generates the unique stall vortices with a high pressure gradient. Under part-load conditions, the combination of rigid vortex stretching, rigid vortex dilation (RVD), coriolis force, and baroclinic torque (BT) cause further increase in the strength of cavitation tail vortices. The RVD and BT caused by diffuser vanes leading edge cavitation can accelerate the development and fusion of leading edge separation vortices, pressure surface separation vortices, and trailing edge separation vortices in the diffuser, then generate unique stall vortices with high pressure gradient in advance. Proper orthogonal decomposition analysis indicates that the unique stall vortices in the diffuser occupy the main energy of the flow pattern. The flow pattern in the diffuser is superimposed by a variety of vortices with different frequency characteristics, and these vortices show a particular low frequency signal well below fn. The cavitation at the diffuser vanes leading edge interacts with vortices to induce leading edge separation vortices and unique stall vortices with low frequency characteristics more easily, and these vortices always dominate the flow pattern evolution.