Abstract
In order to understand the complex nature of the system dynamic phenomena, such as the strong vibration and noise caused by blade passage in the pump turbine, a state-of-the-art three-dimensional (3D) compressible transient simulation would be desirable to study the problem in depth. This study investigated the phase resonance (PR) that occurred during a full-load operation in the turbine mode of a pump turbine on a prototype scale. As a first step, the wave reflection at the boundaries, and the influence of the timestep and sound speeds on the behavior of traveling pressure waves inside a spiral casing, were studied. It was found that nonreflective boundary conditions and an appropriately small timestep are critical to capturing the wave reflection and superposition process inside a spiral casing; a certain kind of direct PR risk was detected in its system design. The detected direct PR differed from the well-known PR with two features: firstly, it was almost independent of the sound speeds, and secondly, the pressure distribution over the spiral circumference varied among the amplitudes. The latter feature was caused by pressure waves at every stator channel induced by a rotor stator interaction (RSI). The 3D flow simulation with an acoustic model, which couples the RSI and PR phenomena, would predict better results for understanding the problem than the simplified one-dimensional (1D) method.
Highlights
Reversible pump turbines have been widely applied in the design and construction of pumped storage projects
The frequency of interest for the project under investigation was 128.6 Hz, which was equal to two times the blade passing frequency (BPF) observed from the prototype operation
This study developed a state-of-the-art 3D CFD transient simulation method based on the acoustic model available in CFX to study the phase resonance that occurred during a full load operation in the turbine mode of a pump turbine on the prototype scale
Summary
Reversible pump turbines have been widely applied in the design and construction of pumped storage projects. Nicolet proposed a one-dimensional (1D) hydroacoustic model based on the matrix transfer method developed by Haban et al [1] and conducted a modeling of RSI for a Francis pump turbine on the model scale with a configuration of nine blades and 20 guide vanes [2]. Zobeiri conducted three-dimensional (3D) incompressible transient flow numerical simulations of RSI and PVR for a similar pump turbine configuration on the model scale [3]. Yan and Koutnik developed a partial 3D compressible simulation method to study RSI in pump turbines [4]. In 2015, Fang and Zhang translated Doerfler’s book on flow-induced pulsation and vibration in hydroelectric machinery published in 2013 [13] into Chinese, which drew the attention of one client and a unit supplier of the project with strong vibrations and noises observed at a turbine full load operation. We were given the opportunity to conduct incompressible and compressible simulations to investigate the internal mechanisms of PR in depth
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