Power Swing Generated in Francis Turbines by Part Load and Overload Instabilities

Valentín, David; Presas, Alexandre; Egusquiza, Eduard; Valero, Carme; Egusquiza, Mònica; Bossio, Matías

doi:10.3390/en10122124

Cited by 76 publications

(43 citation statements)

References 15 publications

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“…This conclusion supports our previous recommendation about selecting a diaphragm with a shutter area ratio from 40% to 60% [34]. Synchronous (plunging) pressure fluctuations can produce variations in head, discharge, torque, and output power known in the literature as a power swing [13]. Equations (5) and (6) are applied for two unsteady signals acquired on the same level to discriminate between asynchronous and synchronous components, respectively: ST +ST 1 2 P(t)= 2 (5) R(t)=ST -P 1 (6) As expected, the equivalent amplitudes associated with the rotating component (RC) are larger than the plunging component (PC) for the case without the diaphragm (Figure 10).…”

Section: Pressure Pulsations Decompositionsupporting

confidence: 89%

“…Synchronous (plunging) pressure fluctuations can produce variations in head, discharge, torque, and output power known in the literature as a power swing [13]. Equations (5) and (6) are applied for two unsteady signals acquired on the same level to discriminate between asynchronous and synchronous components, respectively:…”

Section: Pressure Pulsations Decompositionmentioning

confidence: 99%

“…The fixed blade turbines, i.e., Francis and propeller types, operated at far-away conditions from the BEP, leads to a high level of swirl at the draft tube inlet because of the mismatch between the swirl delivered by the wicket gates and the angular momentum extracted by the runner [12]. Therefore, the decelerated swirling flow in the draft tube cone often results in the vortex breakdown (known as the vortex rope), which is the main cause of the pressure fluctuations generated in the hydraulic turbines at part load conditions [13]. This phenomenon and the associated effects is known in the literature as a draft tube surge [14,15].…”

Section: Introductionmentioning

confidence: 99%

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A Novel Passive Method to Control the Swirling Flow with Vortex Rope from the Conical Diffuser of Hydraulic Turbines with Fixed Blades

et al. 2019

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In this paper, we introduce a novel passive control method to mitigate the unsteadiness effects associated to the swirling flows with self-induced instabilities. The control method involves a progressive throttling cross-section flow at the outlet of the conical diffuser. It adjusts the cross-section area with a diaphragm while maintaining all positions of the circular shape centered on the axis. It improves the pressure recovery on the cone wall while the pressure fluctuations associated with the self-induced instability are mitigated as it adjusts the cross-section area. It can adjust the diaphragm in correlation with the operating conditions of the turbine. We investigated the passive control method on a swirl generator, which provides a similar flow as a hydraulic turbine operated at a partial discharge. The plunging and rotating components are discriminated using the pressure fluctuation on the cone wall to provide a clear view of the effects induced by this passive control method. As a result, the novel proof of concept examined in this paper offers valuable benefits as it fulfils a good balance between the dynamical behavior and the hydraulic losses.

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Section: Pressure Pulsations Decompositionsupporting

confidence: 89%

Section: Pressure Pulsations Decompositionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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A Novel Passive Method to Control the Swirling Flow with Vortex Rope from the Conical Diffuser of Hydraulic Turbines with Fixed Blades

et al. 2019

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“…At part load [37][38][39] (and sometimes at full load [40]), a vortex rope can appear. This vortex rope has a frequency below the rotational frequency of the runner and has the ability to excite the whole hydraulic system [37,[40][41][42]. Nevertheless, the ability of this rope to excite a structural resonance of the runner may be limited as its characteristic frequency is much below the first natural frequencies of the runner.…”

Section: Vortex Ropementioning

confidence: 99%

“…Thus, the characteristics of the cavitation volume are analyzed at one arbitrary temporary point [31,48,49]. Other cavitation phenomena which are characterized by the variation of the cavitation volume, such as the part load and full load unstable vortex rope, are analyzed at different time points during one cycle [41,[50][51][52]. Therefore, although the stochastic pressure fluctuations induced by these vortices are better captured with unsteady CFD models [28,31], the cavity volume, which will be used to compute the natural frequencies of the runner, is determined by the steady CFD model, which is enough to evaluate the risk of a possible resonance.…”

Section: Simulated Cavities At Deep Part Loadmentioning

confidence: 99%

Cavitation Effects on the Structural Resonance of Hydraulic Turbines: Failure Analysis in a Real Francis Turbine Runner

et al. 2018

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When discussing potential resonances in hydraulic turbine runners, cavitation effects are usually neglected. Nevertheless, recent studies have experimentally proved, that large cavitation volumes in the proximity of flexible simple structures, such as hydrofoils, greatly modify their natural frequencies.In this paper, we analyze a resonance case in a Francis runner that leads to multiple fractures on the trailing edge of the blades, after just one day of operation at deep part load. If simple acoustic Fluid-Structure-Interaction (FSI) simulations are used, where the runner's surrounding fluid is considered as a homogenous acoustic medium (water), the risk of structural resonances seems to be limited as the predicted natural frequencies are far enough from the excited frequencies by the flow. It is shown that the only hydraulic phenomenon which could have produced such fractures in the present case is the Rotor Stator Interaction (RSI). In order to analyze possible cavitation effects on the natural frequencies of the turbine runner, CFD simulations of the deep part load conditions have been performed, which predict large inter-blade vortex cavities. These cavities have been then introduced in the acoustical FSI model showing that under such conditions, natural frequencies of the runner increase approaching to some of the RSI excited frequencies. In particular, a possible resonance of the four-nodal diameter (4ND) mode has been found which would explain the fast behavior of the crack propagation. Furthermore, the shape and the position of the real fracture found agree with the local maximum stress spots at the junction between the trailing edges and the crown.Energies 2018, 11, 2320 2 of 16 almost one century ago. More recently, the researches of Amabili et al. [4,5] and Kwak [6] revise and improve the analytical work performed by Lamb. Furthermore, many studies performed in the last decade show that acoustical FSI simulations are perfectly capable to predict natural frequencies of submerged structures [7][8][9]. In all the aforementioned studies simple thin plates have been considered.In the particular case of reaction hydraulic Turbines, which are completely submerged, added mass effects play an important role and have to be considered for the calculation of the natural frequencies as well. In this case the added mass phenomenon is even more complicated, as the gaps turbine-casing (usually considered as rigid boundaries) are extremely small (less than 1% of the turbine diameter), the turbine is rotating, and the water couples the turbine with the casing. Some effects such as rotation [10], influence of non-rigid surfaces [11] and acoustic modes [12] have been recently discussed using numerical FSI simulations and contrasting experimental results. Nevertheless, most of these effects have not been yet determined in real turbines. A review of actual research works shows that for turbine runners in still water, natural frequencies and mode shapes obtained with finite element simulations have a good agreement with exp...

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Forced vibration analysis model for pumped storage power station based on the 1D–3D coupling and pipe walls vibration

Yang

Lian

Wang

et al. 2022

Earthquake Engineering and Resilience

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Hydraulic vibration is a common phenomenon in pumped storage power stations (PSPS) and hydropower plants. Evaluating the performance of the PSPS and water conveyance system under the hydraulic vibration condition is significant for the safety of the electric power and the PSPS system. In this study, the one‐dimensional (1D) and three‐dimensional (3D) coupling model for the entire PSPS system is established based on the open‐source software OpenFOAM and in‐house C++ codes. The coupling data exchange is realized by writing and reading files. The coupling model is validated by comparing the results with the pure 1D method under small load disturbance conditions. The forced vibration source is modeled by the pipe walls vibration method in the 3D region, and the 1D method takes charge of other parts in the PSPS system. The combination of the pipe walls vibration and 1D–3D coupling could fully consider the incident and reflected characteristics of the pressure waves. The established model could evaluate the overall performance of the PSPS system under forced vibration. Sensitive analysis of the vibration magnitude is carried out, and the results are consistent with the theoretical analysis, demonstrating that the established model is applicable for the forced vibration analysis.

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Power Swing Generated in Francis Turbines by Part Load and Overload Instabilities

Cited by 76 publications

References 15 publications

A Novel Passive Method to Control the Swirling Flow with Vortex Rope from the Conical Diffuser of Hydraulic Turbines with Fixed Blades

A Novel Passive Method to Control the Swirling Flow with Vortex Rope from the Conical Diffuser of Hydraulic Turbines with Fixed Blades

Cavitation Effects on the Structural Resonance of Hydraulic Turbines: Failure Analysis in a Real Francis Turbine Runner

Forced vibration analysis model for pumped storage power station based on the 1D–3D coupling and pipe walls vibration

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