Influence of the boundary conditions on the natural frequencies of a Francis turbine

Valentín, David; Ramos, David Alberto Lara; Bossio, Matías; Presas, Alexandre; Valero, Carme

doi:10.1088/1755-1315/49/7/072004

Cited by 20 publications

(26 citation statements)

References 8 publications

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“…The mode shapes of all kinds of Francis turbine runners are similar, especially those with a similar specific speed value, since they have common geometrical characteristics [ 5 , 19 , 20 ]. These mode shapes are formed by different number of nodal diameters (ND) with different relative amplitude between the crown, band and blades [ 8 , 21 ]. If the deformation in the crown is bigger than in the band or in the blades, these mode shapes are called crown-dominant mode shapes (CD) [ 9 ].…”

Section: Dynamics Of a Francis Turbine Runnermentioning

confidence: 99%

“…To determine experimentally the dynamic response of hydraulic turbine runners in operation is challenging, especially in the case of Francis turbines and pump turbines, because the runner of those types of machines is rotating and confined in water, with small gaps and seals, and is strongly affected by boundary conditions [ 7 , 8 , 9 ]. The natural frequencies of this kind of hydraulic turbine runner are affected by the added mass of the surrounding water [ 10 , 11 ], the rotation [ 12 , 13 ] and the distances to the stationary parts [ 7 , 14 ].…”

Section: Introductionmentioning

confidence: 99%

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Feasibility of Detecting Natural Frequencies of Hydraulic Turbines While in Operation, Using Strain Gauges

Valentín

Presas

Bossio

et al. 2018

Sensors

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Nowadays, hydropower plays an essential role in the energy market. Due to their fast response and regulation capacity, hydraulic turbines operate at off-design conditions with a high number of starts and stops. In this situation, dynamic loads and stresses over the structure are high, registering some failures over time, especially in the runner. Therefore, it is important to know the dynamic response of the runner while in operation, i.e., the natural frequencies, damping and mode shapes, in order to avoid resonance and fatigue problems. Detecting the natural frequencies of hydraulic turbine runners while in operation is challenging, because they are inaccessible structures strongly affected by their confinement in water. Strain gauges are used to measure the stresses of hydraulic turbine runners in operation during commissioning. However, in this paper, the feasibility of using them to detect the natural frequencies of hydraulic turbines runners while in operation is studied. For this purpose, a large Francis turbine runner (444 MW) was instrumented with several strain gauges at different positions. First, a complete experimental strain modal testing (SMT) of the runner in air was performed using the strain gauges and accelerometers. Then, the natural frequencies of the runner were estimated during operation by means of analyzing accurately transient events or rough operating conditions.

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Section: Dynamics Of a Francis Turbine Runnermentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Feasibility of Detecting Natural Frequencies of Hydraulic Turbines While in Operation, Using Strain Gauges

Valentín

Presas

Bossio

et al. 2018

Sensors

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“…e way of measuring frequency response found in the literature is with the use of accelerometers and strain gauges, and the excitation methods found is pressure field excitation, impact excitation, or excitation with various vibration mechanisms as electronic muscles and shakers. e surrounding structure of the runner has high impact on the natural frequencies and damping; hence, the analysis should preferably be carried out with the runner mounted in the housing [3,8]. Presas et al analyzed the frequency response of a pump turbine while mounted in the housing, but the use of two electronic muscles was not sufficient to excite all modes [9].…”

Section: Introductionmentioning

confidence: 99%

Experimental Study of a Low‐Specific Speed Francis Model Runner during Resonance

Agnalt

Østby

Solemslie

et al. 2018

Shock and Vibration

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An analysis of the pressure in a runner channel of a low-specific speed Francis model runner during resonance is presented, which includes experiments and the development of a pressure model to estimate both the convective and acoustic pressure field from the measurements. The pressure was measured with four pressure sensors mounted in the runner hub along one runner channel. The mechanical excitation of the runner corresponded to the forced excitation from rotor-stator interaction. The rotational speed was used to control the excitation frequency. The measurements found a clear resonance peak in the pressure field excited by the second harmonic of the guide vane passing frequency. From the developed pressure model, the eigenfrequency and damping were estimated. The convective pressure field seems to diminish almost linearly from the inlet to outlet of the runner, while the acoustic pressure field had the highest amplitudes in the middle of the runner channel. At resonance, the acoustic pressure clearly dominated over the convective pressure. As the turbine geometry is available to the public, it provides an opportunity for the researchers to verify their codes at resonance conditions.

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“…Inside the HYPERBOLE project (FP7-ENERGY-2013-1; Project number 608532) a large Francis unit has been investigated by means of numerical models [1,2] and experimentally on both the reduced scale model of this unit [3][4][5][6] and the real prototype [7].The real unit has a rated power of 444MW and it is located on the British Columbia in Canada. The tests on the reduced scale model (complete model with scale 1/16) were performed in the Laboratory of Hydraulic Machines (EPFL) in Switzerland.…”

Section: Introductionmentioning

confidence: 99%

“…Nevertheless, some operating points can be unstable, limiting the effective operating range of the unit. For this reason, it is of paramount importance to accurately predict (during the design phase of the unit) and to determine (during the operation of the installed unit) these particular points.Inside the HYPERBOLE project (FP7-ENERGY-2013-1; Project number 608532) a large Francis unit has been investigated by means of numerical models [1, 2] and experimentally on both the reduced scale model of this unit [3][4][5][6] and the real prototype [7].The real unit has a rated power of 444MW and it is located on the British Columbia in Canada. The tests on the reduced scale model (complete model with scale 1/16) were performed in the Laboratory of Hydraulic Machines (EPFL) in Switzerland.…”

mentioning

confidence: 99%

Detection and analysis of part load and full load instabilities in a real Francis turbine prototype

Presas

Valentín

Egusquiza

et al. 2017

J. Phys.: Conf. Ser.

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Abstract. Francis turbines operate in many cases out of its best efficiency point, in order to regulate their output power according to the instantaneous energy demand of the grid. Therefore, it is of paramount importance to analyse and determine the unstable operating points for these kind of units. In the framework of the HYPERBOLE project (FP7-ENERGY-2013-1; Project number 608532) a large Francis unit was investigated numerically, experimentally in a reduced scale model and also experimentally and numerically in the real prototype. This paper shows the unstable operating points identified during the experimental tests on the real Francis unit and the analysis of the main characteristics of these instabilities. Finally, it is shown that similar phenomena have been identified on previous research in the LMH (Laboratory for Hydraulic Machines, Lausanne) with the reduced scale model. IntroductionOne of the advantages of using large hydraulic turbines for power generation is that they output power can be adjusted depending on the instantaneous energy demand of the grid. In order to regulate the output power, these units have to operate out of its design conditions. Particularly, many Francis units, which are nowadays the most installed hydraulic turbines in power plants, have to work out of its best efficiency point for long periods of time. Nevertheless, some operating points can be unstable, limiting the effective operating range of the unit. For this reason, it is of paramount importance to accurately predict (during the design phase of the unit) and to determine (during the operation of the installed unit) these particular points.Inside the HYPERBOLE project (FP7-ENERGY-2013-1; Project number 608532) a large Francis unit has been investigated by means of numerical models [1, 2] and experimentally on both the reduced scale model of this unit [3][4][5][6] and the real prototype [7].The real unit has a rated power of 444MW and it is located on the British Columbia in Canada. The tests on the reduced scale model (complete model with scale 1/16) were performed in the Laboratory of Hydraulic Machines (EPFL) in Switzerland.The unstable points of this unit were firstly predicted based on the numerical and experimental studies made on the reduced scale model. As a final step of the HYPERBOLE project, a measurement campaign on the real unit has been performed. One of the goals of this campaign was to determine and to investigate the unstable operating points of the real prototype of the investigated unit.In this paper, the experimental data obtained during the prototype tests are analyzed. The main focus of the analysis is firstly to determine and to analyze the main unstable operating points of the unit. Finally, it is observed that similar phenomena was found in the tests made on the reduced scale model.

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Influence of the boundary conditions on the natural frequencies of a Francis turbine

Cited by 20 publications

References 8 publications

Feasibility of Detecting Natural Frequencies of Hydraulic Turbines While in Operation, Using Strain Gauges

Feasibility of Detecting Natural Frequencies of Hydraulic Turbines While in Operation, Using Strain Gauges

Experimental Study of a Low‐Specific Speed Francis Model Runner during Resonance

Detection and analysis of part load and full load instabilities in a real Francis turbine prototype

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