Fish Friendly Axial Flow Pump Design And Application Based On Blade Strike Model

Axial flow pump is normally applied in the situation of low head and high flow rate owing to its high specific speed.It functions as an important engineering equipment to elevate and transport fluid during water resources scheduling and management,and widely used in flood control,drainage and water transfer to protect property and personal safety.However,a large number of fish suffer from injury and mortality when passing through the conventional pumping station.In this paper,a validated blade strike model is presented to combine theoretical analysis,numerical simulation and model experiment to study fish handling performance in the vaned pump.Based on the BVOP and Vision pumps developed by the dutch company Bosman Water-management,the fish friendly axial flow impeller and vaned diffuser are designed and investigated to reduce fish injury and mortality,and also to keep hydraulic performance acceptable.The main achievements in this paper are as follow:?1?A blade strike model is presented and validated with live fish tests on Vision35mixed flow pump.The tests are carried out at ten operating conditions of the pump and the predicted fish mortality is compared with measured value.The mathematic model is then established to assess fish handling performance of vaned pump.?2?The correlation between specific speed,pump head and fish handling performance is discussed based on the blade strike model.The results show that pump with low head and low specific speed has great fish friendliness,and for high specific speed pump with selected ND,discharge capacity and fish friendliness can be improved with increased pump size D and reduced shaft speed N.?3?The BVOP125-?-140 pump acts as the prototype pump.The hydraulic and cavitation performance are predicted by means of CFD and validated with experimental results,among which the errors between CFD predictions and measurements are systematically discussed.Based on the blade strike model,fish handling performance of prototype pump is predicted within a range of flow rate and head.The prototype pump is a typical axial flow pump causing high fish damage,and the fish friendly designs should be implemented to reduce fish mortality.?4?The fish friendly designs are conducted on the BVOP125-?-140 pump,while an iterative optimization design is employed to improve the hydraulic and cavitation performance of the initial design.Compared with the prototype pump,the final optimization design of the fish friendly pump meets the operation requirements and the fish mortality ratio is reduced from 65%to 15%which is a significant improvement.?5?To reduce blade strike mutilation ratio,the design of non-mutilation blade leading edge is proposed and the forward-swept angle for pumps with different head and specific speed is calculated.The results exhibit that,the higher the pump head and specific speed are,the larger the forward-swept angle will be.For a low specific speed pump,the application of non-mutilation blade leading edge is possible.?6?When the circumferential space for the blade is limited,it is more practical to apply a so-called low-mutilation blade leading edge.The power function is used to describe the forward-swept shape of the leading edge,and the optimal index k and u₁sin?maximum is found to limit the strike velocity in the horizontal?frontal?plane,as a function of hub ratio and forward-swept angle.It can work as a baseline when the fish friendliness is taken into account during the pump design.?7?Then shift the focus to the vaned diffuser in the pump system.The effects of guide vane on fish handling performance is theoretically analyzed to obtain the results that,pump with higher head and specific speed results in larger strike velocity near the guide vane leading edge.The high specific speed pump leads to severe fish damage in the impeller,and also in the guide vane.?8?A fish friendly guide vane is designed to replace the volute of Vision50 pump.The results of performance test show that,fish friendly guide vane improves the discharge capacity of the pump by roughly 20%and the peak efficiency drops by around 0.5%,which is acceptable for practical application.The results of live fish test show that,the fish injury and mortality reduces a lot by replacing the volute with fish friendly guide vane.