The Physical Origin of Severe Low-Frequency Pressure Fluctuations in Giant Francis Turbines

Zhang, R.-K.; Cai, Qingchun; Wu, Jing; Wu, Yi-Liang; Liu, S.-H.; Zhang, L.

doi:10.1142/s0217984905009821

Cited by 26 publications

(19 citation statements)

References 2 publications

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“…The origin of the vortex rope was believed to be closely similar to the vortex breakdown patterns which were observed over a delta wing at a large contact angle [3]. And the inherent unsteadiness of swirling vortex rope was due to the absolute instabilities at the conical inlet of the turbine's draft tube [4]. Following this clue, a novel solution of flow feedback was proposed which stabilized the swirling flow and thus mitigated the vortex rope and its associated pressure fluctuations [5].…”

Section: Introductionmentioning

confidence: 91%

On the Flow Instabilities and Turbulent Kinetic Energy of Large-Scale Francis Hydroturbine Model at Low Flow Rate Conditions

et al. 2014

Advances in Mechanical Engineering

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This paper is to make a better understanding of the flow instabilities and turbulent kinetic energy (TKE) features in a largescale Francis hydroturbine model. The flow instability with aspect of pressure oscillation and pressure-velocity correlation was investigated using large eddy simulation (LES) method along with two-phase cavitation model. The numerical simulation procedures were validated by the existing experimental result, and further the TKE evolution was analyzed in a curvilinear coordinates. By monitoring the fluctuating pressure and velocities in the vanes' wake region, the local pressure and velocity variations were proven to have a phase difference approaching /2, with a reasonable cross-correlation coefficient. Also the simultaneous evolution of pressure fluctuations at the opposite locations possessed a clear phase difference of , indicating the stresses variations on the runner induced by pressure oscillation were in an odd number of nodal diameter. Considering the TKE generation, the streamwise velocity component ⟨ 2 ⟩ contributed the most to the TKE, and thus the normal stress production term and shear stress production term imparted more instability to the flow than other production terms.

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Section: Introductionmentioning

confidence: 91%

On the Flow Instabilities and Turbulent Kinetic Energy of Large-Scale Francis Hydroturbine Model at Low Flow Rate Conditions

et al. 2014

Advances in Mechanical Engineering

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“…In terms of operating condition feature, under low partial load, pressure fluctuation with rotation frequency and other higher frequencies may appear [26,27]. Under the partial load condition, the draft tube vortex pressure fluctuation with a low frequency is taken as the main factor of the pressure fluctuation which may occur in the flow channel [10]. Under the high load area, Karman Vortex, channel vortex, higher part load pressure fluctuation, and so on may appear [28,29].…”

Section: Multidimensional Frequency Band Energy Ratio Feature Extractmentioning

confidence: 99%

“…When the pressure fluctuation resonates with the water body in the pressure pipeline, it will cause the vibration, output oscillation of the hydropower generating unit, and even have an influence on the electric power system [8,9]. In recent years, some large and giant Francis turbines have been put into operation, whose size and specific speed have increased, while relative stiffness has weakened; hence the hydraulic instability problems have become more serious [10]. Therefore, in order to improve the hydraulic stability of Francis turbine, it is necessary to research the inherent mechanism and performance characteristics of the pressure fluctuation and their influences on the operation stability of Francis turbine [11].…”

Section: Introductionmentioning

confidence: 99%

A Novel Multidimensional Frequency Band Energy Ratio Analysis Method for the Pressure Fluctuation of Francis Turbine

Wang

Liang

Yue

et al. 2018

Mathematical Problems in Engineering

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The pressure fluctuation has multiple influence on the steady operation of Francis turbine, and the impact degree varies with the operation condition. In this paper, for the analysis of pressure fluctuation in the Francis turbine, a novel feature extraction method of multidimensional frequency bands energy ratio is proposed based on Hilbert Huang Transform (HHT). Firstly, the pressure fluctuation signal is decomposed into intrinsic mode functions (IMFs) by EEMD. Secondly, the Hilbert marginal spectrum is utilized to analyze the frequency characteristics of IMFs. Then, according to the inner frequency of IMFs, each of them is divided into high, medium, or low frequency band which are constructed based on the frequency characteristic of the pressure fluctuations in the Francis turbine. Afterward, the energy ratio of each frequency band to the original signal is calculated, which is to realize the feature extraction of multidimensional frequency band energy ratio. Actual applications verify that this method not only can extract the time-frequency characteristics but also can analyze the condition feature of the pressure fluctuation. It is a novel method for extracting the feature of pressure fluctuation in the Francis turbine.

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“…Some peculiar phenomena of vortex instability have appeared in the decelerating swirl flow, which are named as vortex breakdown and precessing vortex core (PVC) or precessing vortex "rope". The effects associated with the transformation of an axisymmetric swirl flow in one or more precessing vortexes causes dangerous periodic vibrations on the draft tube walls [1,2].…”

Section: Introductionmentioning

confidence: 99%

Regimes with periodical pressure pulsation in Francis draft tube

2017

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Abstract. The paper reports on results of the experimental study of flow and pressure pulsations in a laboratory model of the draft tube of Francis-99 hydro turbine over a broad range of operating regimes. A novelty is the rapid prototyping and 3-d printing of the inflow swirl generators that makes it possible to acquire rapidly a large amount of experimental data for a variety of designs and operating conditions. The frequency characteristics of flow and the phase-average pressure distribution in draft tube cone have been measured with the aid of special acoustic sensors.

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The Physical Origin of Severe Low-Frequency Pressure Fluctuations in Giant Francis Turbines

Cited by 26 publications

References 2 publications

On the Flow Instabilities and Turbulent Kinetic Energy of Large-Scale Francis Hydroturbine Model at Low Flow Rate Conditions

On the Flow Instabilities and Turbulent Kinetic Energy of Large-Scale Francis Hydroturbine Model at Low Flow Rate Conditions

A Novel Multidimensional Frequency Band Energy Ratio Analysis Method for the Pressure Fluctuation of Francis Turbine

Regimes with periodical pressure pulsation in Francis draft tube

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