Transient simulation of a pump-turbine with misaligned guide vanes during turbine model start-up

It is thought that the pressure fluctuation can occur due to the interaction between flow through guide vanes and flow into runner blades, resulting in a vibration of turbine and a blade cracking, in a hydraulic turbine operated in a wide range for flexible power demand. High accurate velocity measurement with high time/spatial resolution can help to clarify the mechanism of the interaction and to provide good experimental data for the validation of numerical procedure. So the aim of present study is to estimate the unstable velocity field quantitatively in the area between guide vanes and runner blades, using high time-resolved particle image velocimetry (PIV). Two types of velocity measurements were carried out, i.e., phase-locked measurement and high time sequential velocity measurement, in a pump-turbine model with 20 guide vanes and 6 runner blades. The characteristic of the flow field varied corresponding to the operating conditions such as flow rate and rotational speed. Opening angles of guide vanes were kept uniform. A clockwise vortex was generated at inside of the runner blade under smaller rotational speed. A counterclockwise vortex was separated at the backside of the runner blade under higher rotational speed. At any operating conditions, the velocity between guide vanes and runner blades oscillated periodically at the blade passing frequency.

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Distribution of Pressure Fluctuations in a Prototype Pump Turbine at Pump Mode

Advances in Mechanical Engineering ◽

10.1155/2014/923937 ◽

2014 ◽

Vol 6 ◽

pp. 923937 ◽

Cited By ~ 16

Author(s):

Yuekun Sun ◽

Zhigang Zuo ◽

Shuhong Liu ◽

Jintao Liu ◽

Yulin Wu

Keyword(s):

Mass Flow ◽

Pressure Fluctuations ◽

Dominant Frequency ◽

Pump Mode ◽

Pump Turbine ◽

Guide Vanes ◽

Path Direction ◽

Mass Flow Rates ◽

Operating Points ◽

Spiral Casing

Pressure fluctuations are very important characteristics in pump turbine's operation. Many researches have focused on the characteristics (amplitude and frequencies) of pressure fluctuations at specific locations, but little researches mentioned the distribution of pressure fluctuations in a pump turbine. In this paper, 3D numerical simulations using SSTk − ω turbulence model were carried out to predict the pressure fluctuations distribution in a prototype pump turbine at pump mode. Three operating points with different mass flow rates and different guide vanes’ openings were simulated. The numerical results show how pressure fluctuations at blade passing frequency (BPF) and its harmonics vary along the whole flow path direction, as well as along the circumferential direction. BPF is the first dominant frequency in vaneless space. Pressure fluctuation component at this frequency rapidly decays towards upstream (to draft tube) and downstream (to spiral casing). In contrast, pressure fluctuations component at 3BPF spreads to upstream and downstream with almost constant amplitude. Amplitude and frequencies of pressure fluctuations also vary along different circumferential locations in vaneless space. When the mass flow and guide vanes’ opening are different, the distribution of pressure fluctuations along the two directions is different basically.

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Hysteresis Characteristic in Hump Region of a Pump-Turbine Model

10.20944/preprints201608.0007.v1 ◽

2016 ◽

Author(s):

Deyou Li ◽

Hongjie Wang ◽

Jinxia Chen ◽

Torbjørn K. Nielsen ◽

Daqing Qin ◽

...

Keyword(s):

Guide Vane ◽

Pressure Sensors ◽

Low Frequency ◽

Rotational Frequency ◽

Hysteresis Phenomenon ◽

Pump Turbine ◽

Hysteresis Characteristic ◽

Hydraulic Losses ◽

Measurement Direction ◽

Turbine Model

The hump characteristic is one of the major instabilities in pump-turbines. When pump-turbines operate in the hump region, strong noise and serious fluctuations could be observed, which are harmful to the safe and stable operations and even destroy the whole unit as well as water conveyance system. In this paper, a low specific speed (nq = 36.1 min−1) pump-turbine model was experimentally investigated. Firstly, the hump characteristic was obtained under 19 mm guide vane opening. More interestingly, when the hump characteristic was measured in two directions (increasing and decreasing the discharge), the hysteresis characteristic was found during the hump region. The analysis of performance characteristics reveals that the hump instability is resultant of Euler momentum and hydraulic losses, and different Euler momentum and hydraulic losses in the two development processes lead to hysteresis phenomenon. Then, 12 pressure sensors were mounted in the different parts of the pump-turbine model to obtain the time and frequency characteristics. The analysis of fast Fourier transform confirms that the hump characteristic is related to the low-frequency (0.04–0.15 times rotational frequency) vortices. The occurrence and cease of vortices depend on the operating condition and measurement direction, which contribute to the hysteresis characteristic. Finally, the type of the low-frequency vortices was analyzed through the cross power spectrum.

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