| Semi-open impeller submersible sewage pump is an efficient,reliable,non-clogging sewage pump suitable for treating municipal sewage,industrial wastewater and rural domestic sewage containing mixtures of solids,fibers,and liquids,fibers and liquids.It has the features of anti-winding,long continuous and stable running time,automatic control and easy installation,etc.It can play an important role in urban sewage,municipal engineering,industrial drainage system and water conservancy construction.However,the internal flow of semi-open impeller submersible pumps is extremely complex,including internal unsteady flow and obstruction in the end wall area aroused by the leakage flow at the top of the impeller as well as turbulent pulsation,and an in-depth study of these problems and flow mechanisms is useful for understanding and optimizing the design theory and methods of submersible sewage pumps.In this paper,a typical three-blade semi-open submersible sewage pump is selected for internal unsteady flow field analysis and solid-liquid two-phase flow characteristics study,starting from the tip leakage flow,with the financial support of the National Natural Science Foundation of China(No.51979138),the Natural Science Foundation of Jiangsu Province(No.BK20220587)and China Postdoctoral Science Foundation funded project(No.2022TQ0127).In this study,the development process,spatial and temporal characteristics of the vortex in the internal flow field of the submersible sewage pump and its coiling and interference process with other vortex systems in the flow field are explored in depth.Based on the commonly used flow control methods,different end-wall treatment schemes are selected to improve the unsteady flow structure of tip clearance flow inside the semi-open impeller submersible pump and to improve the operational stability of the submersible sewage pump,and these research results can provide some reference and development ideas for the research in the field of submersible pumps to develop new application scenarios.The main research contents and the creative results achieved in this paper are as follows:1.Based on the curvature and rotation modified SST k-ω turbulence model,the external characteristics and internal flow field of semi-open impeller submersible pumps under different flow conditions with different tip clearance sizes are carefully analyzed,focusing on the evolution of the trajectory and intensity of the tip leakage vortex formed due to the tip leakage flow spreading and coiling with the variation of the clearance.It is found that the process of the initial generation,development and dissipation of the vortex can be clearly captured by numerical calculation under the shut-off condition;as the clearance size increases,the spreading roll of the leakage flow promotes the separation of the vortex from the vortex at the top of the blade,and the trajectory of the vortex gradually deviates from the suction surface and enhances the interference with the main flow,while the circumferential "Oscillation" of the vortex core trajectory appears.The intersection of the tip leakage vortex with other flow structures coincides with the high entropy region.The distribution of the components of the vortex transport equation in the flow field is analyzed,and it is found that the trajectory of the leakage vortex also coincides best with the distribution of the Coriolis force term of the vortex equation,and the Coriolis force plays a dominant role in the generation of the leakage vortex and its developmental trajectory under the shut-off condition.From the quantitative analysis of the tip obstruction coefficient,it can be seen that there is a clearance-related threshold for the front-end wall effect,and this threshold is related to the specific case,and the influence is enhanced at small flow conditions.2.Based on the transient numerical calculation results of semi-open impeller submersible pumps with different tip clearance sizes,the spatial and temporal evolution characteristics of the tip leakage vortex within the semi-open impeller submersible pumps are analyzed,and the corresponding temporal frequency of pressure pulsation in the flow field of the tip region is also analyzed.It is found that the coupling between the stall vortex and the leakage vortex is enhanced with the increase of the clearance under the shut-off condition,and the dynamic and static interference between the volute tongue and the impeller significantly affects the trajectory development of the leakage vortex.However,the tip clearance is also the location where flow distortion is most likely to occur.The results of unsteady numerical calculations under rated flow conditions show that the leakage vortex trajectory shows unsteady characteristics under rated flow conditions,but with the increase of the impeller tip clearance,the transient flow field distortion in the middle region of the impeller is obvious and the transient feature is enhanced.3.A semi-open impeller submersible pump external characteristics and pressure pulsation test research,the clearance value on the leading edge of the pressure pulsation caused by overflow has a great impact,small clearance due to the wall effect,the pressure pulsation intensity on both sides of the tip is very close,when the clearance increases beyond a certain threshold,the weakening of the wall effect leads to the leading edge of the vane overflow becomes an important cause of unstable flow in the pump.Under the shut-off condition,the back-flow vortex of the impeller inlet does not cause the pressure pulsation intensity at the monitoring point of the impeller inlet to increase exponentially,instead,the pressure pulsation at the impeller inlet is more excited under the high flow condition,and the increase of the pressure pulsation amplitude at the monitoring point near the volute tongue is more significant under the small flow condition,especially under the shut-off condition,a high pressure pulsation zone appears at the downstream position of the volute tongue.4.The flow control scheme to suppress the tip leakage vortex is explored,and the external characteristics and the evolution process of the vortex leakage are compared and analyzed for the cutting,inverted round and T-shaped leaf top structure schemes.Based on the "jet mixing" theory,the development of the leaf top leakage flow is divided into: initial section,transition section and main body section,and different leaf top structures provide similar linear velocity in the initial section of the leakage flow,and then the velocity decreases and the flow line deflects in the interference with the main stream,and the leakage vortex is formed by spreading and coiling.The numerical calculation results with different leaf top structures show that the T-shaped leaf top can limit the initial velocity of the leakage flow,but will intensify the cross-flow channel motion of the leakage flow;compared with the original and other solutions,the head and efficiency of the T-shaped leaf top are higher,reflecting the better hydraulic performance.5.Numerical simulation analysis of solid-liquid two-phase flow based on Particle model for semi-open impeller submersible pumps with different clearances,and general linear model analysis of the variance of pump performance was performed under the influence of multiple factors.The internal flow characteristics,solid phase distribution law and wear characteristics under each working condition and solid phase parameters were investigated.It was found that the variation of solid phase parameters and tip clearance have significant effects on the efficiency at lower flow rate;and the effect of solid phase concentration on head is enhanced at larger flow rate,and the variance analysis results shows that the solid phase particle size had little effect on the external characteristics of the pump.Under various flow rate conditions,the solid phase particle enrichment area is located at the impeller inlet and outlet position,and the change of clearance size does not alter the distribution pattern of solid phase particles. |
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