Research On The Dynamic Characteristic Of Pump-turbine Based On Fluid Structure Interaction

Pump-turbine,the key of pumped storage power station,face the great challenge in terms of hydraulic characteristics and structural strength under complex and changeable operating conditions.It is especially serious for the vibration and noise of the key components such as runner,shaft system and support bracket under transient hydraulic force.In this paper,dynamic characteristics of pump turbine in transient process based on fluid-structure interaction are studied using numerical simulation.Firstly,a method to simulate the structural response and identify modal under cavitation based on acoustic-structure interaction is proposed.Comparing with experimental results and traditional modal analysis methods,the accuracy and feasibility of this method is verified under cavitation.Based on this method,the influence of the void ratio of the cavity on the natural frequency,mode shape and response is discussed.The mechanism of modal separation is decomposed.That is,when the water or vapor transforms to the mixture,the fundamental mode separate into the fundamental mode and the composite mode.With the change of the void ratio,the characteristics of the fundamental mode and the composite mode show a reciprocal relationship.Secondly,the hydraulic characteristics of a prototype pump turbine during start-up under pump mode and turbine mode are simulated.The unsteady flow characteristics of pipelines and the clearance are primarily focused.The transient simulation method of pump-turbine,with multi-scale and whole flow,is verified by the test data of the prototype pump turbine.It is found that the axial hydraulic force,in runner and clearance including crown and band,is circumferential asymmetric distributed.The hydraulic thrust is affected by both the flow rate and the rotate speed.Finally,the structural characteristics of the support bracket,shaft system and runner of pump-turbine under the influence of asymmetrical hydraulic force of the runner in the transient process are calculated.The displacement of runner is distributed circumferential asymmetrically.The effect of hydraulic force on the support bracket through the shaft mainly play as the resultant force,which conforms to the Saint-Venant principle.During the pump-mode start-up,the stress concentration of support bracket occurs at the connection between the supporting rib and the thrust bearing seat.The stress of the runner is concentrated at the connection between the crown and the blade inlet in the initial stage,and then placed at the connection between the crown and the blade outlet.During the turbine-mode startup,the stress concentration of the runner is located at the connection between the band and the runner inlet before the no-load operation.During the loading stage,it is at the connection between the crown and the runner inlet,and finally moves to the connection between the band and the runner outlet.This research reveals the complex dynamic characteristics and mechanism of fluid-solid interaction during the transient process of pump-turbine,which provides scientific guidance for the optimal design and safe and stable o peration of the unit.