17 research outputs found

    Decomposition of the structural response of the Francis-99 runner during resonance

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    In this work, the complex structural response of the Francis-99 turbine runner is further investigated by decomposition of the output signal from previous Laser Doppler Vibrometry (LDV) measurements into the motion of each nodal diameter. During the structural measurements, the non-rotating runner was installed in the turbine pit, submerged in a non-flowing water, and excited with piezoelectric patches mounted on the hub. The patches were excited with phase shifted sinusoidal voltage to create overall excitation of the runner with a desired number of nodal diameters. The deflection of selected locations on the trailing edges were scanned with LDV, one point at a time, and the global movement was reconstructed by combining the data for all points. The Francis-99 runner has its blades bolted to an over-dimensioned hub and shroud, where the hub is not fully axi-symmetrical and has several hollows in it. This, together with the fact that one patch was found to be non-functional, is believed to have excited other ND patterns in addition to the one that was intentionally excited, therefore contaminating the movement of the trailing edges with movements that does not belongs to the excited ND. To mitigate this and create a better representation of the movement of the trailing edge, which is not affected by the bleed from other ND, the LDV signal for each excited frequency of a particular ND is post-processed using discreet Fourier transformation to decompose the motion of each nodal diameter in the range ND0 to ND7. This unveils the contribution of each nodal diameter within the output signal where a spike is seen for the excited ND in all measurements. Influence from other nodal diameters were found, where the failed patched is believed to cause a ND1 like movement. In addition the clustering of multiple eigenmodes with differing nodal diameters previously found in narrow frequency bands were also found as interfering contribution when exciting at the relevant frequencies. © Published under licence by IOP Publishing Ltd.Decomposition of the structural response of the Francis-99 runner during resonancepublishedVersio

    Optimalisering av ringledning for Peltonturbin

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    Hydroenergi er en norsk produsent av vannturbiner med godt etablert kunnskap innen Kaplan og Francis turbiner. Selskapet har designet flere Pelton skovler med det mål å redusere kavitasjon. Selskapet ønsket å finne et fullstendig Hill-diagram for en av skovlene på en 5 jets Pelton turbin. Andre design skulle bli testet i beste punktet og sammenlignet med nevnte design. I tillegg ønsket de å undersøke optimal design av ringledningen for turbinen. Tester ble utført ved Vannkraftlaboratoriet ved NTNU. Grunnet flere havari i løpet av testperioden ble antall forsøk redusert til kun å finne Hill-diagram som et av designene. Det designet som skulle testes fullt ut ble ødelagt i et av havariene etter at tester med 1 dyse åpen var fullført. De ble erstattet med skovler med samme geometri men med en 2◦ høyere pitch vinkel. Effekten av den økte pitch vinkelen kunne ikke tallfestes. Sammenligning av tester gjort med 1 og 2 dyser indikerer derimot en mulig innvirkning på plasseringen av beste punkter med hensyn til rotasjonshastighet. Et sett av kriterier for optimal design av ringledningen ble funnet og den opprinnelige ringledningen ble redesignet for å møte disse. De redesignede ringledningene gjennomgikk simuleringer i Computational Fluid Dynamics (CFD) basert på tidligere simulering av den opprinnelige ringledningen som er verifisert med eksperimenter. Simuleringene viste en forbedring av falltap ringledningen. I utløpet til dysene ble det observert ugunstig strømning, men dette er antatt å være grunnet feil i modellen. Den hydrauliske virkningsgraden til de testede skovlene ble funnet å være lavere enn på de beste Peltonturbinene på markedet

    Optimalization of Pelton Distributor

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    Hydroenergi er en norsk produsent av vannturbiner med godt etablert kunnskap innen Kaplan og Francis turbiner. Selskapet har designet flere Pelton skovler med det mål å redusere kavitasjon. Selskapet ønsket å finne et fullstendig Hill-diagram for en av skovlene på en 5 jets Pelton turbin. Andre design skulle bli testet i beste punktet og sammenlignet med nevnte design. I tillegg ønsket de å undersøke optimal design av ringledningen for turbinen. Tester ble utført ved Vannkraftlaboratoriet ved NTNU. Grunnet flere havari i løpet av testperioden ble antall forsøk redusert til kun å finne Hill-diagram som et av designene. Det designet som skulle testes fullt ut ble ødelagt i et av havariene etter at tester med 1 dyse åpen var fullført. De ble erstattet med skovler med samme geometri men med en 2◦ høyere pitch vinkel. Effekten av den økte pitch vinkelen kunne ikke tallfestes. Sammenligning av tester gjort med 1 og 2 dyser indikerer derimot en mulig innvirkning på plasseringen av beste punkter med hensyn til rotasjonshastighet. Et sett av kriterier for optimal design av ringledningen ble funnet og den opprinnelige ringledningen ble redesignet for å møte disse. De redesignede ringledningene gjennomgikk simuleringer i Computational Fluid Dynamics (CFD) basert på tidligere simulering av den opprinnelige ringledningen som er verifisert med eksperimenter. Simuleringene viste en forbedring av falltap ringledningen. I utløpet til dysene ble det observert ugunstig strømning, men dette er antatt å være grunnet feil i modellen. Den hydrauliske virkningsgraden til de testede skovlene ble funnet å være lavere enn på de beste Peltonturbinene på markedet

    A reference pelton turbine - design and efficiency measurements

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    The Pelton turbine has been subject to a varying degree of research interest since the debut of the technology over a century ago. Despite its age there are gaps in the knowledge concerning the flow mechanisms effecting the flow through the turbine. A Pelton turbine has been designed at the Waterpower Laboratory at NTNU. This has been done in connection to a Ph.D. project focusing on the flow in Pelton turbine buckets. The design of the turbine has been conducted using in-house knowledge in addition to some comments from a turbine producer. To describe the geometry multiple Bezier curves were used and the design strategy aimed to give a smooth and continuous gradient along the main flow directions in the bucket. The turbine has been designed for the operational conditions of the Pelton test rig installed at the Waterpower Laboratory which is a horizontal single jet test rig with a jet diameter(ds) of 35 mm. The diameter(D) of the runner was set to 513 mm and the width(W) of a bucket 114 mm, leading to a D/W ratio of 4.5. Manufacturing of the turbine has been carried out in aluminium and the turbine has undergone efficiency testing and visual inspection during operation at a head of 70 m. The turbine did not performed as expected and the maximum efficiency was found to be 77.75%. The low efficiency is mainly caused by a large amount of water leaving the bucket through the lip and hence transferring close to zero of its energy to the shaft. The reason for the large lip loss is discussed and two possible causes are found; the jet is located too close to the lip, and the inner surface of the bucket does not lead the water away from the lip. The turbine geometry and all data from both measurements and simulations will be available upon request in an effort to increase the amount of available data concerning Pelton turbines

    Onboard measurements of pressure pulsations in a high head Francis model runner

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    Over the last years, there have been several incidents with cracks in high head Francis turbines. These cracks are understood to be related to pressure pulsations, vibration modulus and the combination of these. In this paper, a setup for the investigation of pressure pulsations in a low specific speed model turbine is presented with the use of onboard pressure sensors. Earlier onboard measurements have mainly utilized blade-mounted sensors. In this paper, a setup with hub-mounted pressure sensors are described. In addition, a position sensor is utilized to analyse the pressure data relative to the angular position of the runner. The setup is considered as a good reference for computational fluid dynamics validation and is considered less extensive for evaluating the onboard pressure pulsations compared to blade-mounted sensors

    Signature Investigation of Typical Faults on Francis Turbines

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    Hydropower is facing new operational strategies as the increasingly competitive power market demands for higher flexibility. Consequently, turbines are forced to handle tougher operation and are prone to more frequent degradation. By implementing a real-time monitoring system, a better understanding of the behavior of components may contribute to detect faults at an earlier stage, reducing potential downtime. This paper will present the work done in the preliminary work of the author’s master thesis. The focus has been to characterize the normal behaviour of a Francis turbine through amplitude and frequency analysis. Steady-state measurements of pressure pulsations have been conducted on the Francis test-rig at the Waterpower laboratory at NTNU. Different hydraulic phenomena and respective frequencies were identified. In addition, the results revealed several unexpected frequencies and suspicious observations, and potential sources of these are discussed. Possible fault detection schemes based on peak-peak and frequency analysis are suggested. Alarm should be raised in case of mismatches in sensor relations, magnitude variations or if new harmonics or frequencies appears

    TwinLab Digital. Twin Laboratory for Hydropower

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    This report summarizes the results from the TwinLab project in 2021. The project was funded by HydroCen OpenCalls and is a multidisciplinary project with partners from all work packages in HydroCen

    On the Rotor Stator Interaction Effects of Low Specific Speed Francis Turbines

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    The rotor stator interaction in a low specific speed Francis model turbine and a pump-turbine is analyzed utilizing pressure sensors in the vaneless space and in the guide vane cascade. The measurements are analyzed relative to the runner angular position by utilizing an absolute encoder mounted on the shaft end. From the literature, the pressure in the analyzed area is known to be a combination of two effects: the rotating runner pressure and the throttling of the guide vane channels. The measured pressure is fitted to a mathematical pressure model to separate the two effects for two different runners. One turbine with 15+15 splitter blades and full-length blades and one pump-turbine with six blades are investigated. The blade loading on the two runners is different, giving different input for the pressure model. The main findings show that the pressure fluctuations in the guide vane cascade are mainly controlled by throttling for the low blade loading case and the rotating runner pressure for the higher blade loading case

    Pressure Pulsations and Fatigue Loads in High Head Francis Turbines

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    The Norwegian power system today includes a relatively large percentage of Francis turbines with a head of above 300m, in the world. This leads to a need to maintain and develop the national competence regarding the challenges connected to this type of turbine. The importance of this competence is increased by the fact that these turbines have a high installed capacity and are therefore crucial to the production stability. In the later years the old runners in Norwegian high head power plants have begun to show signs of fatigue. Taking the average age of these runners, which is approaching 45 years, into account, this may not be surprising. The surprising fact is that the same signs of fatigue, and in some cases total breakdown due to cracks, also occur in new and modern Francis runners. This leads to a hypothesis that the problem stems from sources other than the turbine runners themselves. The suspected cause of this reduction in the expected lifetime is the change the pattern of turbine operation to accommodate new intermittent energy in the power system and progress in the manufacturing technology enabling thinner blades. As an example the Horizon2020 project HydroFLEX initialised by the European Union aim to produce technology that allows for 30 start-stops per day for Francis runner. A research project funded by the Norwegian Research Council and the Norwegian Hydro Power Industry, aim to increase the available knowledge regarding these high head Francis turbines. The research is done both on a basic and applied level where the focus is to increase the knowledge of the phenomena and to produce validation data for numerical simulations of said phenomena. The fundamental research focus on the hydrodynamic dampening applied on a hydrofoil within a high velocity water flow. The applied research is focused on the Francis-99 runner, a model runner of a High Head Francis turbine, which has been instrumented in order to study the Rotor-Stator-Interaction(RSI) and the structural response of the runner. The research areas both consist experimental and numerical studies, where the experimental results are used to validate the numerical. This paper presents the background of the project, the different activities and some preliminary results from selected activities. The aim of the paper is to introduce the project, participants and the participants view on the future of High Head Francis runners that do not crack due to RSI

    Modal testing of the Francis-99 runner

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    The Francis-99 low specific speed Francis runner has undergone much study in the years since it was first made available to the public. The High Head Francis(HiFrancis) project, hosted by the Waterpower Laboratory at NTNU, have conducted multiple experimental campaigns to supply validation data for numerical simulations of the RSI phenomenon for the runner. Due to the amount of instrumentation on board the runner an asymmetry exists in the runner structure that naturally affects the structural response of the runner. From numerical analysis the runner has been found to exhibit multiple natural modes of vibration, within narrow frequency bands. In order to validate the identified natural frequencies, with their corresponding mode of vibration and the amplitude, an experiment has been conducted. The experiment utilises piezo electric patches mounted on the runner hub to excite the runner in a defined mode of vibration and the response at the trailing edge of all blades is measured with a 1D Laser Doppler Vibrometry scanner. Preliminary results are shown that demonstrate the possibilities with the presented experimental method. Francis runner, Vibration, Modal testingpublishedVersio
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