Effects Of The Diffusion Of Impeller Passage On The Performance Of Ultra-low Specific Speed Centrifugal Pump

In recent years, ultra-low specific speed centrifugal pump has been widely applied to every walk of life along with the rapid development of economy, which accelerates the advance in research of the pump. Meanwhile, the mature application of CFD technology provides powerful scientific basis for the analysis of external characteristic and internal flow field for fluid machinery. This paper aims at analyzing the important factors influencing the diffusion of impeller passage, then analyzes effects of the diffusion of impeller passage on the external characteristic and internal flow field of ultra-low specific speed centrifugal pump through CFD numerical calculation.In order to have an overall and comprehensive understanding about the meaning of the diffusion and give simplified definition of the diffusion which is studied in this topic, a large number of books and references have been consulted. The concrete parameters in the definition of the diffusion are analyzed, and giving the important factors influencing the diffusion of impeller passage-blade numbers Z, blade wrap angle (?), outlet blade squeeze coefficient Ψ2.This paper is taking the hydraulic model of ultra-low specific speed centrifugal pump as foundation model, and the computational domain model includes inlet pipe, the impeller passages, volute casing, the front and back chambers and the seal clearance. CFD numerical simulation is carried out on the model. The calculative and experimental results are compared, and the error ranges of head, shaft power and efficiency are smaller at the design condition. Three parameters have important impact on the diffusion of the impeller passage. Divide them into two parts to research the influence and tendency on the impeller passage diffusion. Firstly, we change blade numbers Z, blade wrap angle (?), outlet blade squeeze coefficient Ψ2to vary the impeller passage diffusion. Secondly, we set up a variety of physical model with different diffusion of impeller passage. Then we compare the effects of different diffusion on the performance of ultra-low specific speed centrifugal pump by CFD numerical simulation.From the effects of three parameters-blade numbers Z, blade wrap angle (?), outlet blade squeeze coefficient Ψ2on the diffusion of impeller passage, it is analyzed that the diffusion of the impeller passage increases while the number of blade reduces. For the impeller of different wrap angles, the diffusion decreases with outlet blade squeeze coefficient reducing. For the impeller with the same outlet blade squeeze coefficient, the diffusion drops with blade wrap angle increasing. For the ultra-low speed centrifugal pump, the effects of impeller with different diffusion to the external characteristics and the internal flow field of the pump are compared by numerical simulation. The result shows that the impeller with less blade number. larger blade wrap angle and thicker blade would be better, as considering the head. shaft power, efficiency requirements within the range of reasonable when choosing the impeller of the ultra-low speed centrifugal pump.