Study On The Self-priming Process And High Flow Cavitation Characteristics Of Short Jet Self-priming Pump

The jet self-priming pump is one of the most popular fluid machines in the field of agricultural engineering.With the promotion of smart sprinkler systems,irrigation districts have an increasing demand for short self-priming pumps and higher requirements for their performance.However,the contradiction between self-priming performance and the problem of cavitation easily occurring under high flow conditions has now become an urgent problem to be solved in the process of improving the performance of short jet self-priming pumps.Therefore,the study of the balance between self-priming performance and maximum operating flow is of great significance to improve the performance and operating stability of short jet self-priming pumps.This paper is based on CFX fluid simulation software to numerically simulate the internal flow field,cavitation performance and self-priming performance of a short jet self-priming pump.The internal flow pattern of short jet selfpriming pump is analyzed,and the strength of cavitation suppression performance is compared and investigated for different combinations of nozzle outlet diameter and effuser throat diameter,and the gas-liquid two-phase flow is studied on this basis.The main study contents and findings are as follows:(1)The JET 1100 type short jet self-priming pump was used as the object of study.The full flow field of the short jet self-priming pump was modeled in 3D using UG 3D modeling software and the full flow field was meshed using ICEM software.The external characteristics of the short jet self-priming pump are calculated by numerical simulation and verified by combining with experiments.The predicted results of the external characteristics were found to have a consistent trend with the experimental results at the full flow rate of the operating conditions.It further demonstrates the high accuracy of the numerical calculation method in this paper.(2)CFD numerical simulations were used to calculate the steady and unsteady calculations at different flow rates for short jet self-priming pumps.The internal flow field and the pressure pulsation distribution pattern are analyzed.The results show that the flow pattern in each flow channel in the impeller has asymmetry and the intensity of vortices generated in the impeller flow channel varies at different flow rates.Under the small flow condition(Q=lm3/h),the vortex intensity in the impeller flow path is the largest.As the flow rate increases,the vortex intensity decreases.At high flow rate(Q=5m3/h),no obvious vortex structure is observed in the impeller flow path.Under the full flow condition,the pressure pulsation at the impeller inlet did not show obvious periodicity due to the influence of upstream and downstream disturbances in the flow field.However,the pressure pulsation in the impeller runner is mainly governed by the dynamic and static interference between the impeller and the guide vane;which in turn exhibits a distinct periodicity.Therefore,the ejector structure within the short jet self-priming pump causes the flow field at the front of the impeller to exhibit significant transient characteristics,which in turn leads to temporal instability of the inlet flow to the impeller,which will enhance the intensity of the unsteady flow within the impeller and guide vane.(3)Based on the Zwart-Gerber-Belamri cavitation model,numerical simulations of cavitation in short jet self-priming pumps with different combinations of throat diameters and nozzle outlet diameters were carried out.The results show that among all 25 schemes,the short jet self-priming pump with nozzle outlet diameter D1=7.2mm effuser throat diameter D2=18mm combination has the strongest performance against cavitation.With the increasing flow rate,the total entropy production value within the short jet self-priming pump shows a sharp rise and then fall in the process of cavitation priming and evolution,and the flow point of the sharp rise in total entropy production and the flow point of the sharp fall in head for each scheme are obviously coincident.Meanwhile,the regression equation of the head of the short jet self-priming pump with the throat diameter x1 and the nozzle outlet diameter x2 was obtained based on the pooled fitting of the results of multiple scenarios:{H}m=-7.20+3.43x1-3.76x2.The equation can provide a certain theoretical basis for the design of the ejector structure of short jet self-priming pumps.(4)Based on the homogeneous flow Mixture model,the self-priming process was numerically simulated for a short jet self-priming pump model with different combinations of throat diameters and different nozzle outlet diameters.The results show that among the five schemes with better cavitation performance,the scheme with the shortest self-priming time for the combination of nozzle outlet diameter D1=8.2mm effuser throat diameter D2=17mm.However,taking into account the self-priming performance of the short jet self-priming pump and the maximum operating flow rate,the final choice of nozzle outlet diameter D1=7.2mm effuser throat diameter D2=18mm combination of the program as the optimal solution.During the self-priming process,the gas medium inside the impeller and guide vane can be discharged gradually over time.However,the narrow structure of the pump chamber before and after the impeller leads to the presence of gas media that cannot be discharged inside it at all times.Therefore,in order to further improve the self-priming performance of the short jet selfpriming pump,the geometry of this position can be adjusted to enhance the discharge efficiency of the gaseous medium in the subsequent research process.