Study On Internal Flow And Hydrodynamic Characteristics Of Mixed Flow Pump Device

Open channel pumping station is widely used in agricultural production,flood control and ecological construction because of its small installation space,good cavitation performance,low cost and easy maintenance.In the process of operation,large-scale vortices such as wall vortex,bottom vortex and surface vortex will appear in the water inlet tank of the pump unit.In serious cases,the head and efficiency of the pump station will be reduced,the economic benefits will be reduced,and the damage hazards such as cavitation of the pump unit blades,shafting displacement and unit vibration will be caused,and the service life and safety performance of the pump station will be reduced.In this paper,the energy,velocity vector,surface vorticity,pressure fluctuation,axial force,radial force and free surface calculation model of gas-liquid two-phase flow of the mixed flow pump in the pump station are studied systematically and deeply by the method of theoretical analysis,numerical calculation and test.The main work and research results are as follows:1.The research status of domestic and foreign scholars on the classification and flow characteristics of large-scale vortices in the inlet basin,the influence of structural parameters of the mixed flow pump device on the vortices,and the change of device performance under different working conditions are introduced.2.Based on PIV and high-speed photography technology,the flow distribution at the trumpet tube and water guide cone,the basic shape of the surface vortex zone and the interaction process between the surface vortices were measured,and the numerical simulation was carried out.The research shows that:(1)Under different flow and water level conditions,the head and efficiency of the mixed flow pump device obtained by numerical simulation are within 5% compared with the experimental results;the head decreases with the increase of flow,increases with the increase of water level,and the efficiency first increases slowly and then decreases rapidly with the increase of flow,and increases with the increase of water level;(2)The results of numerical simulation are consistent with the experimental results.The flow velocity distribution in the water guide cone and the trumpet tube is regular flow,which plays a better guiding role;(3)With the decrease of flow rate and the rise of water level,the velocity in the water inlet pool decreases,the intensity of surface vortex decreases,and the depth of liquid surface depression,the volume of air cavity and the length of air belt decrease gradually until they disappear;(4)The surface vortices on both sides of the rear part of the pump directly contact and interact with each other.Some of the vortices on one side of the surface are absorbed by the surface vortices on the other side,resulting in the asymmetry and instability of the surface vortices on the left and right sides.3.The numerical simulation method is used to study the internal flow characteristics of the intake pool of the mixed flow pump under different water level and flow conditions.The research shows that:(1)The hydraulic loss of the inlet pool of the mixed flow pump is in direct proportion to the flow,in inverse proportion to the water level,and the resistance coefficient is in inverse proportion to the flow and water level;(2)With the increase of flow rate,the uniformity of flow velocity distribution at the pump inlet increases first and then decreases,and increases with the increase of water level.The weighted average drift angle decreases with the increase of flow rate and increases with the increase of water level;(3)The flow below the horizontal surface of the water inlet of the trumpet tube in the water inlet pool is relatively regular,and the fluid flows into the trumpet tube from all around along the radial direction,while the flow above the horizontal surface of the water inlet of the trumpet tube is relatively complex.The fluid bypasses the pump,and the boundary layer separation occurs at the back of the pump,forming the surface vortex,and flows into the trumpet tube downward;(4)Under the condition of low water level,the flow speed in the water inlet pool is relatively high and the turbulence degree is high.The bottom vortex appears at the bottom of the pool,which causes the flow asymmetry at the bottom of the pool.With the rise of the water level,the phenomenon disappears gradually.The flow at the liquid level and the horn pipe is more disordered,and the flow is asymmetric at the left and right sides.The surface vortex at one side is sucked in by the surface vortex at the other side.With the rise of the water level,the phenomenon gradually increases Disappear;(5)The total circulation of the characteristic section vortex in the inlet basin increases with the decrease of the horizontal position,increases with the increase of the discharge and decreases with the increase of the water level.4.The numerical simulation method is used to study the hydrodynamic characteristics of mixed flow pump under different water level and flow conditions.The research shows that:(1)The main frequency of the pressure fluctuation at the outlet of the mixed flow pump device is one time of the blade frequency,and the amplitude of the pressure fluctuation at the outlet decreases with the increase of the water level;the main frequency of the pressure fluctuation at the clearance between the impeller and the guide vane is one time of the blade frequency,and the amplitude of the pressure fluctuation at the clearance between the impeller and the guide vane changes little with the increase of the water level,and decreases linearly with the increase of the flow;the average pressure at the front and rear sides of the guide cone and the horn tube increases with the increase of the water level However,with the increase of flow rate,it decreases;(2)The upstream inflow directly flows into the pump from the front,the short path energy loss is small,and the back liquid enters the pump in the form of surface vortex,the long path energy loss is large,so the inflow from the front is more than that from the back,which is more significant with the increase of flow rate and the decrease of water level;(3)The main frequency of axial force of mixed flow pump impeller is 1 times of blade frequency,and the amplitude decreases with the increase of water level.At high water level,it first increases and then decreases with the increase of flow,and at low water level,it first decreases and then increases;at small flow condition,the radial force scatter diagram of impeller is triangular,and at large flow condition,it is circular;the average radial force of impeller decreases with the increase of water level,and first increases with the increase of flow,then decrease and increase.