Flow-Induced Vibration of Non-Rotating Structures of a High-Head Pump-Turbine during Start-Up in Turbine Mode

Abstract

Pumped storage-power plants play an extremely important role in the modern smart grid due to their irreplaceable advantages in load peak-valley regulation, frequency modulation, and phase modulation. The number of start-stops per day of pump-turbine units is therefore also increasing. During the start-up transient process in turbine mode, the complex flow in runner passage, crown and band chambers, and seal labyrinth is able to induce severe vibration of non-rotating structures such as head cover, stay-ring, and pose a threat to the safe operation of the pump-turbine unit. In this article, the flow-induced vibration of the structures of a pump-turbine unit during its start-up process in turbine mode is studied. In the first place, this investigation establishes a three-dimensional model of the full flow passage and carries out a full three-dimensional CFD calculation based on one-dimensional pipeline calculation results for the start-up transient process. In the next place, by applying the fluid–structure interaction calculation method, the finite element analysis of non-rotating components of the pump-turbine unit is carried out. The flow-induced stresses and deformations of head cover, stay-ring, etc., are obtained and analyzed. The results reveal that the maximum deformation of the non-rotating structures is located at the inner edge of the head cover while the maximum stress appears at the trailing edge fillet of a stay vane. In summary, the dynamic stress of the non-rotating structures changes largely during the start-up process. The stress is strongly related to the axial thrust caused by the fluid flow. The achieved results can provide guidance for further fatigue life assessment of non-rotating structures and contribute to the structural safety design of pump-turbine units.

Numerical Investigation of Flow and Structural Characteristics of a Large High-Head Prototype Pump–Turbine during Turbine Start-Up

“…Therefore, some scholars adopt the research method of combining the one-dimensional characteristic line method with the three-dimensional flow calculation, and use the inlet and outlet hydraulic characteristics such as pressure and flow rate obtained from the one-dimensional calculation of the pipeline as the boundary conditions of the three-dimensional flow calculation of the unit, so as to realize the solution of the structural response of the unit. [21,22]. Researchers have further confirmed the reliability of the numerical investigation according to the field measurement data for the turbine start-up of the pump-turbine units [23,24].…”

A Field Test Study on the Instability of a Pump-Turbine under Turbine Mode

“…The fluid instability certainly has an impact on the structural components. The dynamic stress distribution of the runner blades during the start-up process 2 of the pump turbine was preliminarily analysed through short-time Fourier transform (STFT) [5], and the effects of pressure fluctuation on the structural stress and bearing thrust of the unit during the startup process of the pump turbine were studied [6]. In terms of vibration, Cao et al [7] studied the wet mode of the runner under cavitation state, found that cavitation will affect the asymmetry of the added mass matrix.…”

Variations of flow patterns and pressure pulsations in variable speed pump-turbine during start-up process

“…During the variable speed start-up process of a unit equipped with a FSFC, different control strategies will result in different start-up operating trajectories. When the unit operates in an operating zone with poor flow patterns, the pressure pulsations will significantly increase, leading to aggravated vibration and damage to the unit [9][10][11]. Therefore, it is necessary to discover the flow patterns and pressure pulsations that may occur in different operating conditions during the unit start-up process, in order to judge the quality of the operating conditions and avoid undesirable conditions in actual operation.…”