The Research On The Structure And The Hydraulic Performance Of Twin-Runner Propel Pump

Traditionally,the power plant of high power,large diameter and low shaft speed is mainly used to improve the performance of the water-jet propulsive pump.However,when the speed of the impeller shaft is reduced,the flow rate on the impeller in the central basin will be lower and the wo rk efficiency will be reduced.In order to solve this problem,we design a kind of twin-runner water-jet pump with parallel structure.The hydraulic performance of the double bypass pump is studied by numerical simulation method,which provides a reference for the design of this kind of propulsion pump.The research details and final conclusions of this research are as follows:1.Confirm the structure and impeller size of the double bypass pump and the optimal bypass ratio.The proper hub ratio should be stud ied when drawing the external pump,considering the influence of the hollow on the hub strength,and the size of the external pump can be obtained by calculating the modulus of torsion section.The hydraulic characteristics of each pump are studied and the optimal bypass ratio is established.The hydraulic performance of the twin-runner pumps of different groups was compared,especially the influence of the hub ratio of the external pump on the hydraulic performance.The dimensionless parameter C is defined as the flow increase rate of the unit total inlet area.When the ratio of internal and external culvert is 0.45,the flow rate increases the most,and the thrust increase of the double-culvert pump is about 9% more than ordinary axial pump.As the flow per unit area increases with the hub ratio,the axial flow pump has a significantly smaller lift from the saddle area to the working point,and the axial flow pump has a larger lift and no obvious change in efficiency.However,the lift drops significantly at the working point,and the overall efficiency declines slightly.2.Research the influence of nozzle shape on hydraulic performanceThe effect of nozzle contraction coefficient on the performance of twin-runner pump was studied,and it was found that the single nozzle twin-runner pump with nozzle contraction ratio of 0.4 had better hydraulic performance.3.Research the performance advantages and disadvantages of twin-runner pump.The twin-runner pump with optimum shrinkage ratio under three different nozzles is simulated,and the performance of the twin-runner pump propeller is further elaborated.Among them,the single nozzle double bypass pump with a nozzle contraction ratio of 0.4 has better hydraulic performance,but compared with the ordinary axial flow pump,the head is about 12% lower,and the efficiency is about 6% lower.The results show that the twin-runner water-jet propulsion pump uses the structure of aero-engine for reference,and the thrust increase s about 9%.It has strong adaptability near the working point,gentle variation of head flow,steady force on impeller and stable outlet flow.The disadvantage is that the efficient area is narrow,and the adaptability is insufficient under low working conditions.The lift decreases by about 12%,and the efficiency decreases by about 6%.