Analysis Of Internal Flow And Runner Dynamics Of High-Head Pump-Turbine Based On Fluid-Solid Coupling

Pumped storage power station,as the current efficient energy storage method,ushered in the opportunity of vigorous development.In order to pursue performance improvements such as high head,large flow rate,and high efficiency,the runner blades of the pump turbine are designed to be long and thinner,as well as the transition process of the pump and turbine is complicated and the conversion between different working conditions is rapid and frequent,resulting in increased stress and strain of the core component runner,and may cause resonance.Based on the fluid-solid coupling calculation method,this paper studies the internal flow and dynamic characteristics of the pump turbine under non-design conditions,which has important theoretical value and practical significance.The main work and conclusions are as follows:Using CFX and Mechnical software,the turbulence model selects RNG k-? to perform unidirectional steady-state fluid-solid coupling calculations on 6 different operating conditions.Comparison with the test results verifies the validity of this calculation,and analysis shows that there are so much secondary flow in the runner area,which will cause the upstream part of blade to bear greater shearing force under high flow conditions.The area with the largest stress distribution in the runner is the junction between the blade inlet edge and the upper crown,and it is also the most vulnerable part.After strength check,it meets the actual operating requirements.The maximum deformation part of the blade is in the middle of the inlet edge,and the deformation amount increases slightly with the increase of the flow rate.The application of fluid-solid coupled unidirectional and bidirectional calculation methods in high-head pump turbines was compared and explored.Using unsteady analysis of the external characteristics,internal flow field and stress and strain calculated by the unidirectional and bidirectional fluid-solid coupling strategy,it is concluded that the blade deformation has little effect on the performance of the pump turbine,what's more the disturbance of internal flow field can only change the local pressure distribution in the inlet area of the blade with large deformation.The unidirectional and bidirectional coupling all capture the characteristic frequency of the atypical 13-fold rotation frequency fluid excitation force in the watershed.The excitation is ge nerated at the runner's leafless region and the inlet watershed,where there is a combined evolution of the separation vortex of the trailing edge of the movable guide vane and the leading edge of the blade.Moreover,the amplitude of pressure pulsation fr equency from 40-fold to 60-fold rotation is more prominent than that of unidirectional fluid-structure coupling.Based on the calculation module in ANSYS,the natural frequency of the runner is obtained,compared with the unsteady fluid excitation frequency and the frequency margin is calculated.It is found that a local Z-direction resonance with a main frequency of 13 times the rotation frequency is generated at the inlet edge of the runner blade.The displacement information of the measurement points at the same position of the solid coupling also shows a consistent motion law,and there are some high-order resonances with little strength.Since the two-way fluid-solid coupling also considers the influence of the subtle deformation of the runner runner,the coupling vibration occurs at the blade inlet,which results in the calculation result of the two-way coupling amplitude being much larger than that of the one-way.The load history obtained by the unsteady two-way fluid-solid coupling calculation is converted into a rain flow load matrix.After the fatigue life calculation is performed by the damage superposition method,the T-joints of the water inlet edge and upper crown and lower ring of the high-head pump turbine are obtained.It is the most vulnerable part of the whole runner,and the excitation force is more complicated under low flow conditions,which is more likely to cause fatigue damage to the runner.At the same time,the high stress amplitude has a greater damage to the runner than the number of stress cycles.