Investigation of Pressure Fluctuation and Pulsating Hydraulic Axial Thrust in Francis Turbines

Xing, Zhou; Shi, Changzheng; Miyagawa, Kazuyoshi; Wu, Haijun; Yu, Jinhong; Ma, Zhu

doi:10.3390/en13071734

Cited by 11 publications

(6 citation statements)

References 39 publications

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“…It is evident from the figure that the periodic behavior of pressure fluctuation is governed by both frequencies. The low frequencies of 0.32, 0.64, and 0.96 times the runner rotational frequency correspond to the rotating vortex rope (RVR) frequency and its harmonics [41]. The bigger frequencies of 200 Hz, 400 Hz, and 600 Hz correspond to the guide vane passing frequency and its harmonics.…”

Section: Pressure Pulsations Inside Runnermentioning

confidence: 99%

Leakage Vortex Progression through a Guide Vane’s Clearance Gap and the Resulting Pressure Fluctuation in a Francis Turbine

et al. 2021

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A clearance gap (CG) between guide vanes (GVs) and facing plates exists at both ends of a Francis turbine and allows the opening angle to be adjusted for varying operating conditions. Leakage flow is induced through this gap due to the pressure difference between the two sides of the guide vanes. While some research works have used qualitative approaches to visualize and predict the strength of a leakage vortex (LV), this paper presents a method for quantifying vortices along a trajectory. In this paper, a prototype high-head Francis runner with specific speed of 85.4 is considered as a reference case. A systematic investigation across both space and time is carried out, i.e., analysis of the spatial temporal progression of LV for three operating conditions. While travelling from the CG to runner leading edge, LV evolution and trajectory data are observed and the values of vorticity and turbulent kinetic energy are calculated for the LV trajectory. Frequency spectrum analyses of pressure oscillations in the vaneless space, runner blade, and draft tube are also performed to observe the peak pressure pulsation and its harmonics. Unsteady fluctuations of the runner output torque are finally studied to identify the patterns and magnitudes of torque oscillations.

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Section: Pressure Pulsations Inside Runnermentioning

confidence: 99%

Leakage Vortex Progression through a Guide Vane’s Clearance Gap and the Resulting Pressure Fluctuation in a Francis Turbine

et al. 2021

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“…Compared with other sources of energy, hydropower is considered as the clean energy with many unique advantages. 1 For example, hydropower simultaneously obtains the advantage of environment-friendly and high-efficiency when hydro-turbines operating in the grid. And as a significantly potential energy, hydropower is doomed to play an important role in energy-transformation.…”

Section: Introductionmentioning

confidence: 99%

Runner cone drilling and slotting to reduce vortex rope - induced pressure fluctuations in a Francis turbine

Qin

Zhang

et al. 2023

Proceedings of the Institution of Mechanical Engineers, Part A:

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Pressure fluctuations caused by helical vortex rope in the draft tube is one of the main reasons for the instability of Francis turbines. Previous studies showed that drilling holes on runner cone can reduce the amplitude of pressure fluctuation. In this study, based on the runner cone which has been drilled one hole, two kinds of new runner cones are designed by means of drilling two more holes (2 holes runner cone) and drilling a slot (2 holes and 1 slot runner cone). Pressure fluctuation and flow pattern observation experiments as well as numerical simulations at partial load operation condition in a Francis turbine were carried out for the three types of runner cones. Analyses were performed to reveal the generation mechanism of the low frequency pressure fluctuations. The results showed that low frequency fluctuations are related to the cyclical rotation of helical vortex rope. Holes and slots on the runner cone have little impact on the efficiency of the Francis turbine. Slotting on the runner cone can reduce the amplitude of pressure fluctuation induced by vortex rope to a maximum of 29.41%. Hence, proper slotting on the runner cone can effectively reduce the low-frequency fluctuation caused by vortex rope in Francis turbines. These findings provide a new idea to improve the hydraulic instability of Francis turbines induced by vortex rope.

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“…Obviously, the numerical method could obtain the time variation law of the hydraulic thrust, and the relationship between the hydraulic thrust and the operating condition can be determined with less cost. 10 Therefore, the numerical method is widely used to evaluate the hydraulic thrust of the hydro turbine. 6,11,12 Some researcher also study the radial hydraulic thrust characteristics of the pump-turbine, and the effect of rotational inertia 13 and cavitation 14 has been discussed.…”

Section: Introductionmentioning

confidence: 99%

Effect of the pressure balance device on the flow characteristics of a pump-turbine

Luo

Wang

2022

Proceedings of the Institution of Mechanical Engineers, Part A:

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Pump-turbine plays a significant role in the pumped storage station, and it is troubled by unreasonable hydraulic thrust. Some pressure balance devices have been adopted to ensure the safety of the pump-turbine unit, but the effect mechanism has not been numerical studied. This paper establishes the CFD model of the flow passage of a pump-turbine, wherein the crown gap, band gap, pressure balance pipe, and the discharge ostium are considered. Then, the flow characteristics of the pump-turbine at four typical operating conditions in turbine mode are calculated in transient scheme, and the numerical results agree with the experimental results. Finally, the effect of the pressure balance pipe and the discharge ostium on the pressure pulsation and the hydraulic thrust is discussed. The results show that the pressure balance pipe causes the direction of the axial hydraulic thrust to change from downward to upward, and the discharge ostium helps reducing the axial hydraulic thrust to a reasonable range. The pressure balance pipe and the discharge ostium have little effect on the radial hydraulic thrust. The pressure pulsation analysis provides a basis for revealing the mechanism of the hydraulic thrust frequency, and the rotor-stator interaction frequency exists in the axial hydraulic thrust. This paper provides a deeper knowledge of the impact mechanism of the pressure balance pipe and discharge ostium on the flow characteristics of the pump-turbine, which could contribute to future designs of the pump-turbine units, and is helpful for improving the safety of the pumped storage unit.

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Investigation of Pressure Fluctuation and Pulsating Hydraulic Axial Thrust in Francis Turbines

Cited by 11 publications

References 39 publications

Leakage Vortex Progression through a Guide Vane’s Clearance Gap and the Resulting Pressure Fluctuation in a Francis Turbine

Leakage Vortex Progression through a Guide Vane’s Clearance Gap and the Resulting Pressure Fluctuation in a Francis Turbine

Runner cone drilling and slotting to reduce vortex rope - induced pressure fluctuations in a Francis turbine

Effect of the pressure balance device on the flow characteristics of a pump-turbine

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