Optimization Research On Hydraulic Characteristics Of The Clearance Flow Between Stator And Rotor Of Full Tubular Pump Unit

Full tubular pump is a new type of tubular pump with electromechanical-pump integrated which simplifies the traditional tubular pump structure,with the advantages of short construction period,low investment,easy and quick installation.However,due to the existence of clearance flow between stator and rotor,it disturbs the flow field distribution in the impeller and hinders the flow of the main stream,resulting in the occurrence of energy loss,pressure fluctuation and noise,which eventually may affect the normal operation of the pump unit.This paper took Longkungou North stormwater drainage pumping station as the research object and the influence mechanism between the design of the edge,the width of inflow&outflow of the stator-rotor clearance and its hydraulic characteristics was investigated by numerical simulation.According to the analysis results and combined with Doehlert Matrix Design-Response Surface Methodology,the design of the clearance between stator and rotor of full tubular pump unit was improved and the corresponding optimized scheme was obtained.Finally,a physical model test of the full tubular pump unit was conducted to check whether the pump design and the optimized solution were reasonable.The research contents of this paper and the research results are as follows.（1）The design of the edge of stator-rotor clearance of a full tubular pump can affect its overall performance parameters by altering the hydraulic parameters of clearance flow between stator and rotor,which is mainly reflected by its influence on the working performance of the impeller chamber of the pump unit and its internal water flow characteristics.While its influence on the hydraulic characteristics of the front guide vane,rear guide vane and discharge channel of the pump unit is relatively smaller.The effect on the external characteristic curve of the pump unit is mainly reflected by the flow-efficiency performance of the pump unit when operating in the saddle area,with a maximum impact rate of 3.88%.（2）Variations in inlet and outlet clearance width of stator-rotor clearance of a full tubular pump have a greater impact on the hydraulic characteristics of the clearance flow between stator and rotor which in return will exert significant influence on the comprehensive performance of the full tubular pump unit.To be specific,the reasonable design of the inlet and outlet clearance widths can enhance the head of the full tubular pump unit by 89.5%and the efficiency performance by 8.8%.For the model pump unit of Longkungou North Stormwater Drainage Pumping Station,the overall priority sequence of the schemes of inlet and outlet clearance width is P3>P2>P1>P4>P6>P5,that is when the inlet and outlet clearance width is 6mm,the relevant overall performance of pump unit is optimal which can be considered as a priority.（3）Considering the overall operating efficiency of the full tubular pump unit as the research index,the outer systolic section x₁ of the inlet clearance of the stator-rotor is the key factor,while the inner extension section t₂,the outer extension section t₁ and the inner systolic section x₂ are all secondary factors.Considering the uniformity of flow velocity at the outlet section of the outflow channel of the full tubular pump unit as the research index,t₁ and t₂ are the key factors,while x₁ and x₂ are both secondary factors.Considering the average vortex angle of the outlet section of the full-tubular pump unit as the research index,x₁ and x₂ are the key factors,while t₁ and t₂ are both secondary factors.After the numerical simulation and verification analysis,the final optimization scheme of the outer ring clearance flow inlet and outlet clearance size is determined as follows:outer extension section t₁=4.921r（r is the clearance with between stator and rotor）,outer systolic section x₁=0.624r,inner extension section t₂=3.655r,inner systolic section x₂=1.6r.（4）By conducting the physical model test of the full tubular pump unit of Longkungou North Stormwater Drainage Pumping Station,it can be found that the pump unit tested has good working performance which can operate in the high-efficiency zone.The cavitation margin was sufficient and the flyaway speed of its pump unit was reasonable,which can ensure the security of the pump unit under the condition of backflow.The amplitude of pressure pulsation was small and the alteration was very little,so the phenomenon of hydraulic resonance didn’t occur during the operation of the pump unit tested.Through numerical simulation and physical model verification,the optimized inlet and outlet clearance structure between stator and rotor of the full tubular pump unit in this paper can improve the comprehensive performance and internal flow pattern of the full tubular pump unit,along with the cavitation performance,flyaway performance and pressure pulsation performance satisfied.Hence,it can be effectively applied in the full tubular pump station.The relevant research results provide some reference value and significance for the comprehensive optimization design of full tubular pump unit.