Solid-liquid Two-phase Flow And Wear Properties Of Pump Turbine Under Pump Condition

In hydropower generation,the good operating conditions of pump-turbines are the premise to ensure the stability of power grid operation and improve the efficiency of generating units.Many river basins have high sediment particle content.During the operation of hydropower stations,sediment will collide with the flow components and cause wear and tear,affecting the normal operation of equipment.Therefore,it is very important to study the internal flow characteristics and solid-liquid two-phase flow of pump-turbines for the efficient and stable operation of units.In this paper,the internal flow characteristics of pump-turbine pump are studied,and the solid-liquid two-phase flow numerical calculation is carried out by Fluent-EDEM coupling method.The flow field distribution and velocity variation of particles in the pump under different physical conditions are analyzed.The Relative wear model is used to predict the location of wear.The normal cumulative force and tangential cumulative force of important components are analyzed,and the location where wear is easy to occur and wear is more serious under pump conditions is obtained.The main results are as follows:（1）The internal flow characteristics of three different flow conditions of 0.8Q_des,1.0Q_desand 1.2Q_des are explored.It is found that with the increase of flow rate,the pressure distribution decreases as a whole,and the velocity and turbulent kinetic energy distribution increases as a whole.The entropy generation theory is introduced to analyze the energy loss distribution of runner,volute,movable guide vane and fixed guide vane.It is found that the energy dissipation in the wall region increases with the increase of flow rate,and the energy dissipation in the mainstream region decreases first and then increases,and the energy dissipation in the wall region is always greater than that in the mainstream region.Under large flow conditions,the hydraulic loss of the unit during operation is mainly affected by the volute.When the flow rate increases,the vortex intensity of the main flow components increases,and the entropy production rate increases.The pressure fluctuation in the runner is analyzed by setting monitoring points.It is concluded that the flow rate is one of the important factors affecting the pressure fluctuation in the runner,and the flow rate is positively correlated with the runner pressure.The greater the flow rate,the more severe the pressure fluctuation.（2）The Fluent-DEDM coupling calculation method is used to simulate the solid-liquid two-phase flow of the pump-turbine pump condition,mainly for the three physical conditions of different sediment concentrations,different flow conditions and different particle sizes.The results show that with the increase of sediment concentration,the sedimentation velocity of sediment particles decreases and the average velocity of particles increases,but the average velocity of sediment particles with different concentrations is basically the same with time.When the flow rate increases,the kinetic energy obtained by the particles from the water flow increases,the particle followability is enhanced,the low-speed particles in the inlet area of the movable guide vane are significantly reduced,and the particle accumulation in the volute is weakened.When the flow rate increases,the average velocity of sediment particles increases,and the velocity distribution of sediment particles gradually disperses.With the increase of sediment particle size,the overall running speed of particles in the flow channel decreases,and it is easy to gather in the volute.When the particle size is small,the impact velocity of water flow on sediment particles is large,and the average velocity of particles fluctuates greatly.After the particle flow is stable,the average velocity of particles is inversely proportional to the particle size.When the particle size gradually increases,the number of high-speed particles obtained is more and the particle velocity distribution is more concentrated.With regard to pressure fluctuation,the increase of particle concentration can reduce the pressure fluctuation in the runner channel,and the pressure fluctuation in the volute becomes violent with the increase of concentration.Under different flow conditions,sediment particles weaken the influence of flow factors on pressure fluctuation,and the trailing edge of runner blade is the position with large pressure fluctuation.The pressure fluctuation decreases with the increase of particle size.（3）The relative wear model is used to predict the position of wear.The normal cumulative force and tangential cumulative force of the main flow components are analyzed,and the position where wear is easy to occur and wear is more serious under pump conditions is obtained.Under different particle concentrations,the wear first occurs at the trailing edge of the blade near the outlet of the runner channel.As the concentration increases,the wear position expands along the trailing edge of the blade to the leading edge of the blade pressure.Under the same particle concentration,the normal cumulative contact energy of the flow components is greater than the tangential cumulative contact energy,indicating that the tangential wear of the particles on the flow components is greater than the normal wear.Under different flow conditions,the trailing edge of the runner blade and the pressure surface of the blade near the front cover plate have always been easy to wear.When the flow rate increases,the kinetic energy obtained by the sediment particles also increases.The position of the pressure surface of the runner blade near the back cover plate becomes a serious wear part,and gradually expands along the trailing edge of the runner blade pressure surface to the leading edge of the blade.Under large flow conditions,the wear of volute wall and guide vane blade is more serious,and the normal and tangential cumulative contact energy of each component increases,but there is the same change rule under different flow conditions.With the increase of particle size,the area of cumulative tangential force and cumulative normal force decreases gradually,the force is more concentrated,and the wear area decreases accordingly.The momentum of the particles given by the water flow is reduced,which leads to the accumulation of particles in the volute,reduces the flow capacity of the volute flow channel,and increases the collision chance between the particles.The wear degree of the volute wall is weakened and the wear area is reduced.When the particle size increases,the normal and tangential cumulative contact energy of each component increases steadily with time,and the change law tends to be consistent.