Detection of Draft Tube Surge and Erosive Blade Cavitation in a Full-Scale Francis Turbine

Escaler, Xavier; Ekanger, Jarle V.; Francke, Hakon H.; Kjeldsen, Morten; Nielsen, Torbjørn Kristian

doi:10.1115/1.4027541

Cited by 26 publications

(24 citation statements)

References 4 publications

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“…[11][12][13]; however, no study has been reported on the investigation of synchronous-and asynchronous-type pressure pulsations in prototypes. Measurements on the model turbines are not completely representative of the prototype and its dynamic behavior [11,[14][15][16][17]. An isolated test facility available in the laboratory has different dynamic characteristics [5,18] and has limited scope for scaling the data.…”

Section: Introductionmentioning

confidence: 99%

Investigation of the unsteady pressure pulsations in the prototype Francis turbines – Part 1: Steady state operating conditions

Trivedi

Gogstad

Dahlhaug

2018

Mechanical Systems and Signal Processing

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Hydropower is one of the most reliable renewable sources of electricity generation. With high efficiency and good regulating capacity, hydropower has the ability to meet rapid changes in power demand. Large investments in intermittent renewable energy resources have increased the demand for balancing power. This demand has pushed hydraulic turbines to generate electricity over the operating range from part load to full load. High-amplitude pressure pulsations are developed at off-design conditions, which cause moderate damage to the turbine components. The pressure pulsations may be either synchronous-(axial)-type, asynchronous-(rotating)-type or both. In this study, pressure measurements on low specific-speed prototype Francis turbines were performed; one of them was vertical axis and another was horizontal axis type. Four pressure sensors were mounted on the surface of the draft tube cone. Pressure measurements were performed at five operating points. The investigations showed that, in the vertical axis turbine, amplitudes of asynchronous pressure pulsations were 20 times larger than those of the synchronous component; whereas, in the horizontal axis turbine, amplitudes of asynchronous pressure pulsations were two times smaller than those of the synchronous component.

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Section: Introductionmentioning

confidence: 99%

Investigation of the unsteady pressure pulsations in the prototype Francis turbines – Part 1: Steady state operating conditions

Trivedi

Gogstad

Dahlhaug

2018

Mechanical Systems and Signal Processing

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“…Č erneticˇ8 and Č udina and Prezelj 14,28 measure the structural vibration signals in audible spectra of kinetic pumps to research the cavitation process and discrete frequency is found. The vibrations and AEs have been combined by Escaler et al 29 to experimentally investigate the draft tube swirling flows and cavitation over the full range of operation in a full-scale Francis turbine. The correlation between the transient cavitating flow structures and the vibration characteristics is analyzed for a modified NACA66 hydrofoil in Wang et al's 30 research.…”

Section: Introductionmentioning

confidence: 99%

Investigation on the vibration and flow instabilities induced by cavitation in a centrifugal pump

Yuan

Parameswaran

et al. 2017

Advances in Mechanical Engineering

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Numerical calculations and experimental measurements were carried out in a closed hydraulic test rig to investigate the vibration characteristics and instabilities induced by the development of cavitation in a centrifugal pump. The internal flow characteristics in the impeller and vibration signals at four different positions of the pump system were analyzed during the cavitation process. The results revealed that the occurrence and development of cavitation could be effectively detected by the sudden increase in the intensity of vibration at the testing points. Corresponding relationships were formulated between the occurrence and the development of cavitation and the intensification of the vibration at the measuring locations. It was found out that the virtual incipient for cavitation was much smaller than the traditional ''critical'' point.

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“…The methods used to predict cavitation are based on induced high frequency vibrations and acoustic emissions measured on the turbine guide bearing and the guide vanes [2]. A preliminary investigation [3] has already demonstrated the feasibility of the installed measuring system and the applied signal processing techniques to monitor the activity of runner blade cavitation for unit operation above the best efficiency point (BEP). The results are consistent with the hypothesis that the highest risk of erosion would occur at full load.…”

Section: Introductionmentioning

confidence: 99%

Assessment of Remote Cavitation Detection Methods with Flow Visualization in a Full Scale Francis Turbine

Escaler¹,

Vilberg²,

Ekanger³

et al. 2018

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

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This paper describes the experimental investigations carried out in the Francis turbine at Svorka power plant operated by Statkraft in Norway. The unit, with a head of 260 m, can deliver a maximum output load of 25 MW. The rated flow rate is 11 m 3 /s and the machine rotates at 600 rpm. The turbine runner shows cavitation pitting on the suction side of the blades but some blades present more erosion than others. Moreover, preliminary studies based on remote monitoring of vibrations and acoustic emissions in this particular unit have predicted risk of erosion at high loads and the presence of a draft tube swirl affecting the cavity dynamics. In order to assess the sensitivity of these methods and the validity of the predictions, several acrylic-glass windows have been installed on the draft tube wall to visualize the runner outlet flow during operation. A high speed camera has been used to record the flow field during the tests with rates up to 5000 frames per second. A cavitation detection system has been installed comprising three high-frequency uniaxial integrated electronics piezoelectric (IEPE)-type accelerometers and an acoustic emission sensor, mounted in the turbine guide bearing pedestal and a guide vane arm. In particular, a series of measurements at different operation conditions have been carried out to correlate the simultaneous camera observations with the acceleration and acoustic emission overall levels in high frequency bands. The preliminary analysis of the camera records permits to certify the existence of erosive blade cavitation with the closure region close to the eroded areas at high loads. It can be seen that cavitation appears only in some blades and that it presents different cavity sizes for the same operation condition. As the load increases towards maximum powers, both the number of blades with cavitation and the size of the cavities grow. Moreover, the overall vibration levels also rise as expected.

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Detection of Draft Tube Surge and Erosive Blade Cavitation in a Full-Scale Francis Turbine

Cited by 26 publications

References 4 publications

Investigation of the unsteady pressure pulsations in the prototype Francis turbines – Part 1: Steady state operating conditions

Investigation of the unsteady pressure pulsations in the prototype Francis turbines – Part 1: Steady state operating conditions

Investigation on the vibration and flow instabilities induced by cavitation in a centrifugal pump

Assessment of Remote Cavitation Detection Methods with Flow Visualization in a Full Scale Francis Turbine

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