Vibration and fatigue caused by pressure pulsations originating in the vaneless space for a Kaplan turbine with high head

Abstract

Purpose -Hydraulic instabilities are one of the most important reasons causing vibrations and fatigues in hydraulic turbines. The present paper aims to find the relationship between pressure pulsations and fatigues of key parts of a Kaplan turbine. Design/methodology/approach -3D unsteady numerical simulations were preformed for a number of operating conditions at high heads for a prototype Kaplan turbine, with the numerical results verified by online monitoring data. The contact method and the weak fluid-structure interaction method were used to calculate the stresses in the multi-body mechanism of the Kaplan turbine runner body based on the unsteady flow simulation result. Findings -The results show that vortices in the vaneless space between the guide vanes and blades cause large pressure pulsations and vibrations for high heads with small guide vane openings. The dynamic stresses in the runner body parts are small for high heads with large guide vane openings, but are large for high heads with small guide vane openings. Originality/value -A comprehensive numerical method including computational fluid dynamics analyses, finite element analyses and the contact method for multi-body dynamics has been used to identity the sources of unit vibrations and key part failures. EC 30,3 448 1. Introduction Kaplan turbines are very efficient over a range of operating conditions since the runner blades are movable and the guide vanes can be turned to any angle to match the blade angle. With increases in unit capacities and runner diameters in recent years, units have experienced stability problems such as hydraulic vibrations and cracks in the large hydraulic turbines. The energy transfer in a turbine is accompanied by pressure pulsations caused by vortices, cavitation and other complex flow phenomena in the flow field, which can result in excessive vibrations, leading to structural fatigue failures. Most research in the literature has focused on pressure pulsations in the flow path. For example, Wang et al. (2002) studied the pressure pulsations caused by rotor-stator interactions in the Three Gorges hydraulic turbines. Guedes et al. (2002) simulated unsteady rotor-stator interactions in a pump-turbine with the unsteady computation results validated by LDV and PIV measurements. Muntean et al. (2004) analyzed the flow in the spiral casing and distributor of a Kaplan turbine to obtain information on channel vortices at different operating conditions. Gehrer et al. (2006) used numerical flow simulations to optimize Kaplan turbine runner. Liu et al. (2009a, b) predicted the pressure pulsations in the entire flow passage of a model Kaplan turbine using 3D turbulent unsteady flow simulations with the predicted pressure pulsations at different points along the flow passage agreeing well with test data in terms of their frequencies and amplitudes. Motycak et al. (2010) studied runner-draft tube interactions of low head Kaplan turbines by numerical simulations and model tests. Petit et al. (2010) compared simulation results with e...

Investigation of the Starting-Up Axial Hydraulic Force and Structure Characteristics of Pump Turbine in Pump Mode

“…They found that the stress caused by hydraulic force is one of the main reasons of the runner fatigue failures and cracks. In terms of the other essential components of pump turbines, Luo et al [32][33][34] focused on the stress of the rotor bracket of the generator and the piston rod of the blade. Improvements in design are made based on stress analyses.…”

Simulation of steady and unsteady flows through a small‐size Kaplan turbine

“…5 They may run of-river without a significant water storage, 6 but their hydraulic efficiency is not high compared to large Kaplan turbines added to water feeding not stable. Kaplan turbines have a rather large vaneless space inducing a complex dissipation of vanes' wakes and vortices, causing large pressure pulsations, 7 added to the flow rotation and secondary flows near the hub and shroud, which are difficult to capture. 8 The energy transfer is accompanied by pressure oscillations caused by vortices, cavitations, and complex unsteady flow phenomena inducing excessive blade vibration.…”

Evaluation of gap influence on the dynamic response behavior of pump-turbine runner

“…In this method, all components of the hydraulic excitation force frequencies are included by using the pressure loads on the runner surfaces obtained from unsteady flow simulation as boundary condition for the dynamic stress analysis. However, the early attempts did not take into account the fluid added mass (Zhou et al, 2007;Wang et al, 2013;Luo et al, 2013).…”