Study On The Cavitation Flow Control Of The Low Specific Speed Centrifugal Pump

Low specific speed centrifugal pump is a special centrifugal pump,usually the speed between 30?80, with high head, small flow, large impeller diameter and other characteristics.When the impeller inlet or runner outlet pressure reduces to saturated vapor pressure, the impeller or the runner blade suction surface will be the occurrence of cavitation, which triggered a series of flow changes and internal changes, such as non steady turbulent fluctuation intensifies, cavitation and burst caused by liquid compressibility, the blade loading of dramatic changes. External changes include dump pump head, efficiency decline, in the running process of the noise increases, piping vibration.This paper adopts the methods of theory analysis, numerical simulation and experimental study on NACA0012 airfoil and different forms of low specific speed centrifugal pump as the research. It focuses on low specific speed constant lift pump, low specific speed stainless steel stamping and welding design method, the heart pump cavitation changes, lift drop and blade load change, and the cavitation flow control methods. The main research contents and innovation achievements include:(1) The improved Kubota cavitation model is given. It is to verify the calculation precision between Kunz cavitation model and improved Kubota cavitation model on NACA0012 airfoil. It provides an alternative cavitation model. Based on improved Kubota cavitation model and airfoil head slotted control technology for NACA0012 airfoil cavitation flow control, the cavitation flow of the angle of 3 degrees, 5 degrees, 7 degrees and cavitation number 0.7 and 0.8 typical six conditions are calculated. It is found that the head slotting on attached cavitation can be effectively controlled.(2) Based on an improved cavitation model and the RNG k-? turbulence model to top suction centrifugal pump, cavitation flow in a single stage is solved numerically. The bubble evolution process, the cavity structure and the type of bubble are explored, and the bubble flow pattern is obtained by analogy. The results show that the inlet pressure of the blade is reduced, and the suction surface of the blade is attached to the suction side of the blade. With the pressure of the near one step down, the bubble will be moved to the front cover of the impeller, and attached to the front cover on the liquid flow caused by blocking.Under the design condition, the number of primary cavitation number and the number of severe cavitation is different. Vapors appear firstly in the backboard in meridian plane, and then attach near the impeller outlet. Centrifugal pump cavitation flow of the external characteristic and reason of aircraft dump across the frozen area are similar, because of the blade type line changed.(3) The mathematical relationship between the head and the flow rate, the flow rate and the power of the low specific speed constant head pump are derived. The hydraulic design of the impeller is givenand the relationship between the low specific speed constant head pump and the low specific speed centrifugal pump is compared. It is the same that with the increase of flow rate, efficiency and power in a condition of high flow are the sudden drop. In the impeller outlet position has obvious flow wake, great flow loss caused.The biggest difference in the flow of change for low speed constant head pump head impact is not great. This is good to improve the low specific speed centrifugal pump small flow overpressure problem.(4) Based on the theory of offset short blades of low specific speed constant head pump impeller of a modified and successfully control blade outlet position of the pressure and velocity distribution. It is found that the low specific speed constant head and efficiency can be improved obviously when the bias short blade is slightly in the axial vortex area of the impeller. According to the length of blade and Bezier curve control impeller design method of secondary modification of the impeller, it is found that the length of leaf blades and the impeller head is generally higher than that of only the long blade of the impeller. Under the design condition, the impeller efficiency is higher than the original Bessel curve design of the impeller. The two modifications are very successful.(5) Using the NACA0012 airfoil slot jet technology, the 6 kinds of blades on the low specific speed constant head pump are designed. By Kubota cavitation model and RNG k-?improved turbulence model, the cavitation flow is simulated numerically. The results show that the operation in the large flow condition, the reason of the blade cavitation damage dump on the low specific speed constant head pump characteristic is cavitation attached,which changes the blade type line, blocks the entire channel and causes the blade pressure surface and the suction surface pressure quickly, causing work ability gradually losing.With reasonable selection of the slit width and angle, it is not only can improve the efficiency of the centrifugal pump, but also can improve the performance of low specific speed centrifugal pump cavitation, reduce NPSH and delay the pump cavitation phenomenon.lt provides a choice to broaden the scope of the pump.(6) Under the cavitation flow control of the low specific speed constant head it is the analysis of a specific speed 33 centrifugal pump cavitation, and slit design on the blade head. The results show that the efficiency of the numerical prediction of the M33-12.5 model pump is about 3% higher than that of the test value. The predicted NPSHR is 1.847m,the test value 1.81M, and the error 2.04%. According to the model of cavitation flow control is effective, it can delay the occurrence of cavitation slotted head.(7) According to the design of the research group, 5 Hermite interpolation function of the stainless steel stamping and welding of low specific speed centrifugal pump CP220A as the research model, it is given stamping and welding process and carried out the research on cavitation characteristics.On the pressure surface of the blade, it has no cavitation area obviously, especially in the design condition. The width of gap has effect on maximum flow rates point. The pump 2# and pump 3# with the 1mm and 1.5mm gap respectively and pump 4# have wider efficient areas.The flow control technique of stainless steel stamping and welding impeller can be manufactured to large-scale production.