Research On The Influence Of Cavitation Performance Of Bypass Guided Jet To Low Specific Speed Centrifugal Pump

The centrifugal pump as key equipment of liquid conveying system,how to improve the running stability has been a hot issue for scholars.Hydraulic performance and cavitation performance are important indicators to measure the performance of centrifugal pumps.Analyzing of the internal flow and cavitation characteristics of centrifugal pumps is significant for the safe and stable operation.The use of the ejector device is one of the effective means to improve the cavitation performance of the centrifugal pump.In order to study the effect of the bypass jet on the cavitation performa nce of centrifugal pumps,the centrifugal pump with a low specific speed of 32 was used as the research carrier.A bypass ejection device is set on the eighth section of the volute near the entrance side.A part of the high-pressure fluid in the volute is injected into the suction chamber of the centrifugal pump,and it is fully mixed with the low-energy fluid in the suction chamber,thereby increasing the pressure at the inlet of the impeller and achieving the result of improving the cavitation performance.The effect and mechanism of high-pressure jet on cavitation control were studied under different cavitation numbers through the combination of numerical simulations and experiments.The main research contents and conclusions are as follows:(1)According to Rotodynamic pumps-Hydraulic performance acceptance test-Grades 1,2 and 3,hydraulic performance tests and cavitation performance tests under three flow conditions of 0.6Q0,1.0Q0,and 1.25Q0(Q0 For design flow)of the prototype pump were first performed on a closed test bench,,performance curves and cavitation characteristic curves at three different flow conditions were drawn and analyzed.Then,under the design condition,the cavitation performance tests were performed on the centrifugal pump with the bypass ejection pipe.As a result,it was found that a single bypass jet incident vertically can effectively delay cavitation generation and control cavitation shedding in the centrifugal pump.(2)Based on the modified SST k-ω turbulence model and Kubota cavitation model,the prototype pump and the bypass pump were numerically simulated and compared with the experimental results.It is found that the simulation results and the test results are closed in value and the curves changes are similar.which proven the reliability of numerical simulations.The head and efficiency of the bypass pump are slightly lower than the prototype pump at each operating conditions in the tests and numerical simulations;the cavitation of nascent cavities and the shedding of cavities are effectively delayed and controlled;the bypass water caused a certain disturbance to the flow in the centrifugal pump,and also had a significant impact on the flow pattern in the suction chamber,which deteriorated the flow stability.(3)The annular incidence structure was used to study the hydraulic performance and cavitation characteristics of the centrifugal pump.The orthogonal test method was used to analyze the two geometric parameters of the number of inci dent nozzles,the angles of incidence,and the operating parameter of flow return rate influenced on hydraulic performance and cavitation performance of the centrifugal pump.First,when the number of nozzles is 4,compared with other number of nozzles,the cavitation performance of the centrifugal pump is the best.Then,when the incident angle is 25°,it is compared with other incident angles.the cavitation performance of the centrifugal pump is the best.The greater the amount of return,the stronger the boosting range and working intensity of the suction chamber,and the better the cavitation performance of the pump,but the greater the declin e in pump hydraulic performance.On the premise of comprehensive consideration of hydraulic performance and cavitation performance,a comparative analysis of the prototype pump and the ejection pump with combined parameters of the number of nozzles is 4,the incident angle is 25°,and the amount of lead-back is 8% of the design flow under the design conditions was carried out.The head and efficiency of the ejection pump are lower than the prototype pump,and the cavitation performance is improved.Compared with the single incident high pressure jet vertical incidence scheme,the superiority of the annular incident structure is verified.