New insight in Francis turbine cavitation vortex rope: role of the runner outlet flow swirl number

Favrel, Arthur; Pereira, João Gomes; Landry, Christian R.; Müller, Andres; Nicolet, Christophe; Avellan, François

doi:10.1080/00221686.2017.1356758

Cited by 67 publications

(39 citation statements)

References 19 publications

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“…For each tested ED n value, measurements are performed until a ED Q value for which the cavitation vortex dynamics lose its coherence and the first eigen frequency cannot be determined accurately. This phenomenon is discussed in more details in [9]. Figure 1(a) for low  values.…”

Section: The Value Of Cmentioning

confidence: 76%

“…Froude numbers, and five different speed factors. The two Thoma numbers, min  and max  , are defined using a similar approach to the one adopted in [9]. The last line of Table 1 presents additional measurements focused on the effects of the Thoma number variation on the cavitation compliance.…”

Section: Experimental Setup and Cavitation Compliance Determinationmentioning

confidence: 99%

“…The swirl number S is defined as the ratio between the axial flux of angular momentum and the axial flux of axial momentum and was originally proposed by Gupta et al [10]. As the swirl intensity and the cavitation compliance in a vortex rope are strongly related, Favrel et al proposed Equation (4) for the calculation of the swirl number at the Francis turbines outlet [9]. As presented in [9], points with similar σ, same Froude number and varying ED n presented resonance conditions when operating at the same swirl number.…”

Section: Swirl Numbermentioning

confidence: 99%

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Measurements of Cavitation Compliance in the Draft Tube Cone of a Reduced Scale Francis Turbine Operating at Part Load

Pereira¹,

Favrel²,

Landry³

et al. 2018

Proceedings of the 10th International Symposium on Cavitation (CAV2018)

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Francis turbines operating at part load conditions typically experience a cavitation vortex rope immediately at the runner outlet. As the compliance of this cavitation flow is much higher than the one in cavitation-free conditions, a decrease in the value of the eigen frequencies of the hydraulic circuit is observed. One of the eigen frequencies can eventually match the frequency of the vortex precession, which acts as an excitation source for the hydraulic system, inducing strong pressure pulsations and output power swings. To predict such undesirable resonance conditions in hydropower plants, the cavitation compliance in the draft tube cone can be identified beforehand at the model scale. This paper presents the identification of the cavitation compliance on a reduced scale model of a Francis turbine over a wide range of part load operating conditions, for different Thoma and Froude numbers. The first eigen frequency of the test rig is firstly identified by modal analysis. The cavitation compliance is then defined by adjusting a 1-D numerical model of the test rig to match this first eigen frequency. These compliance results could then be transposed to the prototype scale, enabling the prediction of the first eigen frequency of the hydropower plant in any part load condition.

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Section: The Value Of Cmentioning

confidence: 76%

Section: Experimental Setup and Cavitation Compliance Determinationmentioning

confidence: 99%

Section: Swirl Numbermentioning

confidence: 99%

See 1 more Smart Citation

Measurements of Cavitation Compliance in the Draft Tube Cone of a Reduced Scale Francis Turbine Operating at Part Load

Pereira¹,

Favrel²,

Landry³

et al. 2018

Proceedings of the 10th International Symposium on Cavitation (CAV2018)

View full text Add to dashboard Cite

show abstract

“…The internal flow and vortex rope characteristics inside the draft tube under the low flow rate conditions depend on the flow and velocity characteristics at the outlet of the runner, which is closely related to the swirl intensity. Therefore, this study used the swirl number S, defined below, to indicate the ratio between the axial fluxes of angular and axial momentum as a representation of the swirl intensity characteristics at the runner outlet, as follows [26][27][28][29]:…”

Section: Vortex Rope Characteristics According To Flow Ratementioning

confidence: 99%

Inter-Blade Vortex and Vortex Rope Characteristics of a Pump-Turbine in Turbine Mode under Low Flow Rate Conditions

Kim

Suh

Choi

et al. 2019

Water

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Pump-turbines are often used to provide a stable power supply with a constant frequency in response to intermittent renewable energy resources. However, existing pumped-storage power stations often operate under off-design conditions because of the increasing amounts of inconsistent renewable resources that have been added to the grid. Under off-design low flow rate conditions, inter-blade vortex and vortex rope phenomena usually develop in the runner and draft tube passages, respectively, in turbine mode. These vortices cause complicated flow patterns and pressure fluctuations that destabilize the operation of the pump-turbine system. Therefore, this study investigates the influence of correlation between the inter-blade vortex and vortex rope phenomena under low flow rate conditions. Three-dimensional steady- and unsteady-state Reynolds-averaged Navier–Stokes equations were calculated with a two-phase flow analysis using a shear stress transport as the turbulence model. The inter-blade vortices in the runner passages were captured well at the low flow rate conditions, and the vortex rope was found to develop within a specific range of low flow rates. These vortex regions showed a blockage effect and complicated flow characteristics with backflow in the passages. Moreover, higher unsteady pressure characteristics occurred at locations where the vortices were especially pronounced.

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“…Strong pressure pulsations, instabilities in the draft tube and excessive turbulence can generate excessive vibration levels and stresses that can damage the machine [3][4][5][6]. Flow instabilities are basically caused by the interaction of the vortex rope produced in the draft tube with the overall system [7][8][9]. It is also known that flow instabilities at part load and overload can produce power fluctuations on the electrical grid (power swing).…”

Section: Introductionmentioning

confidence: 99%

Extension of Operating Range in Pump-Turbines. Influence of Head and Load

Valero

Egusquiza

et al. 2017

Energies

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Due to the increasing share of new renewable energies like wind and solar in the generation of electricity the need for power regulation and energy storage is becoming of paramount importance. One of the systems to store huge amounts of energy is pumped storage using reversible hydropower units. The machines used in these power plants are pump-turbines, which can operate as a pump and as a turbine. The surplus of electrical energy during low consumption hours can be converted into potential hydraulic energy by pumping water to a higher level. The stored energy can be converted into electricity again by operating the runner as a turbine. Due to new regulation requirements machines have to extend the operating range in order to match energy generation with consumption for the grid stability. In this paper the consequences of extending the operating range in existing pump-turbines have been studied. For that purpose, the data obtained after two years of condition monitoring were analyzed. Vibrations and pressure fluctuations of two pump-turbines of 85 MW each have been studied during pump and turbine operation. For turbine operation the effects of extending the operating range from the standard range of 45-85 MW to and increased range of 20-85 MW were analyzed. The change in vibration levels and signatures at very low load are presented with the identification of the phenomena that occur under these conditions. The influence of head in the vibration behavior is also presented. The appearance of fluid instabilities generated at part load that may produce power swing is also presented. Finally, the effect of head on the vibration levels for pump operation is shown and analyzed.

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New insight in Francis turbine cavitation vortex rope: role of the runner outlet flow swirl number

Cited by 67 publications

References 19 publications

Measurements of Cavitation Compliance in the Draft Tube Cone of a Reduced Scale Francis Turbine Operating at Part Load

Measurements of Cavitation Compliance in the Draft Tube Cone of a Reduced Scale Francis Turbine Operating at Part Load

Inter-Blade Vortex and Vortex Rope Characteristics of a Pump-Turbine in Turbine Mode under Low Flow Rate Conditions

Extension of Operating Range in Pump-Turbines. Influence of Head and Load

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