| With the progress of science and the development of computer technology,the research on the flow mechanism of the centrifugal pump has gradually developed and matured.Cavitation is a harmful phenomenon,which usually occurs in hydraulic machinery.It not only reduces the hydraulic performance,but also causes noise and vibration,and even gives rise to the impeller material loss,decreases the life expectancy of hydraulic machinery.The lowest pressure area is located on the suction side of the centrifugal pump blade leading edge near the shroud,where is the most easily occurred cavitation and erosion.A prototype centrifugal pump model of M86-100 is considered to investigate the effect of the slot jet on the energy performance of centrifugal pump.Turbulence effects are considered by using the RNG k-?turbulence model and the Reyleigh-Plesset model is applied as the cavitation mode.Based on the principle that the high energy liquid is introduced to the cavitation region to improve the cavitation performance of the impeller,the slot is designed directly on the impeller shroud near the suction side of the blade leading edge.Based on the theory of pulse jet,a new type of slot pulse jet pump is designed by modifying the impeller front side chamber.The main works and results are as follows:1.A new type of slot impeller is proposed through the redesign of the impeller.The slot jets with 5 different sizes of the slots are designed to investigate the effect of slot size on the pump performance.The steady non-cavitation flow simulation was carried out and the result shows that the slot leakage results in the increase of the impeller flow rate.Compared with the prototype pump,the pump head of slot jet pump decreases.The leakage flow from the impeller front side chamber to the slot can reduce the pump efficiency for most of the flow range.The slot jet can effectively suppress the serious reverse flow in pump at low flow rate,and then the pump efficiency is improved.2.To improve the convergence speed,the steady non-cavitation flow simulation result is taken as the initial value for the steady cavitation flow simulation.The result shows that the slot jet can effectively improve pump cavitation performance,especially at small flow rate.To some extent,the smaller of the slot size,the better of pump cavitation performance.Cavitation performance of the slot impeller with size of2mm?1.75mmhas exceeded the prototype impeller greatly.3.The slot jet mechanism is that the jet flow compensates the blade inlet flow certain energy,and the available net positive suction head is improved.The lowest pressure near the slot impeller blade inlet and the pressure of all forepart regions are improved significantly.So slot jet can improve the cavitation performance of the pump effectively.4.Based on the slot steady jet pump with the size of 4mm×3.5mm,two types of slot pulse jet pumps with different pulse frequency are proposed.The steady non-cavitation flow simulation is carried out and the result shows that the hydraulic performances of slot pulse jet pump agree well with that of slot steady jet pump.There is merely a head jumping point of slot pulse jet pump?at 0.4Q_d.5.The unsteady cavitation simulations are performed based on the steady cavitation simulation to improve the pump cavitation performance.The result shows that to a certain degree,the cavitation performance of slot pulse jet pump is better than that of slot steady jet pump,especially at design condition.The cavitation performance of slot pulse jet pump II is the best.To some degree,the higher of the pulse frequency,the better of the cavitation performance for the slot pulse jet pump.6.The slot pulse jet mechanism is that pulse jet forms a greater velocity shear layer and has a better energy transfer characteristics.Pulse jet compensates a certain energy to the region of the impeller inlet,further improving the pressure at the minimum pressure point of the impeller,and effectively avoiding cavitation damage. |
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