| When the jet centrifugal pump works in large flow rate conditions,it is easy to cavitate in the pump,which resultes in a sharp increase in noise and a steep drop in head and efficiency.These problems have become one of the important factors restricting the safe and stable operation of the jet centrifugal pump in multi-operating conditions.However,there are few reports on the mechanism and performance optimization of related phenomena.In this paper,the cavitation characteristics of the jet centrifugal pump were studied by numerical simulation and experimental measurement.The internal relations between the cavitation characteristics of the jet centrifugal pump and the high velocity circulating jet flow and the strong shear flow structure in the jet device are explored.The main research contents of this paper are as follows:1.A test system was built and performance tests were carried out at different installation heights respectively.Experimental result shows that to a certain extent,with the increase of flow rate,the head curve,the power curve and the efficiency curve drop sharply.As the installation height increases,steep fall point shifts to the low flow rates condition.2.The single-phase numerical calculation of jet centrifugal pump was carried out using ANSYS-CFX software.The internal flow field information of jet centrifugal pump under different flow rate is analyzed.It is found that the low pressure of the jet centrifugal pump appears in the nozzle throat due to the high-speed jet flow of the nozzle exit.The energy exchange in the jet device is basically completed before the diffusion phase.The strong shear flow structure and the vortex flow in the jet centrifugal pump are the important sources of energy loss of this type of pump.3.The influence of area ratio m on the performance of jet centrifugal pump is analyzed,and the flow field information of three kinds of jet centrifugal pump with different area ratios was studied.The area ratio of the jet device has a great influence on the performance of the jet centrifugal pump.With the increase of the area ratio,jet centrifugal pump head curve slope is continuously decreasing.jet centrifugal pump efficiency increases with the increase of area ratio.Input power decreases with the increase of area ratio.The smaller the area ratio,the more energy the jet nozzle provides to the impeller inlet.4.In large flow rate condition,the head and efficiency of jet centrifugal pump decrease sharply.In order to study the mechanism of the performance steep drop and the flow structure,The numerical simulation under each operating condition was carried out at 0m installation heights.The pressure distribution,cavitation distribution and velocity cloud diagram of the middle section of the pump are analyzed.The reason of cavitation occurres in the throat of the jet device is explained.In order to analyze the influence of the jet device on the cavitation performance of the pump,the outlet of the nozzle is filled out,and the cavitation performance of the pump is analyzed by numerical method.Two kinds of jet device with different area ratio are designed,the effect of area ratio on cavitation performance of jet centrifugal pump is analyzed.The results show that the numerical simulation results agree well with the experimental data.The relative error of the pump head H and the efficiency is2.46%and 1.12%in design condition.Cavitation flow point of numerical simulation is 0.5m~3/h larger than that of the experimental test.Because of its small area ratio,the jet shear layer is quickly extruded to the wall of the throat,and the lowest pressure region appears after the nozzle in jet device,and cavitation appears at the place firstly.As the flow rate increases,cavitation region extends rapidly to the inlet of impeller.The performance steep fall point of jet centrifugal pump is exactly the cavitation inception flow point in the pump,the cavitation performance of a jet centrifugal pump depends on the cavitation performance of the jet device.The jet device can improve the head and self-priming performance of the centrifugal pump,but high speed circulatory flow and strong shear flow in the jet device would decrease the efficiency and cavitation performance greatly.As the area ratio increases,the cavitation inception flow point increases,the cavitation performance of the pump increases,the pump power decreases,and the efficiency increases. |
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