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dc.contributor.advisorDahlhaug, Ole Gunnar
dc.contributor.advisorNielsen, Torbjørn
dc.contributor.advisorThapa, Bhola
dc.contributor.authorThapa, Biraj Singh
dc.date.accessioned2017-01-09T09:29:14Z
dc.date.available2017-01-09T09:29:14Z
dc.date.issued2016
dc.identifier.isbn978-82-326-1859-0
dc.identifier.issn1503-8181
dc.identifier.urihttp://hdl.handle.net/11250/2426677
dc.description.abstractErosive wear of turbine components has been a major operational challenge for the runoff-river hydropower plants across the basins of Himalaya in Asia. The hard mineral particles, which are carried by rivers reach the turbines and erode the surface in contact. In Francis turbines, guide vanes, cover plates, hub at runner inlet and blades at runner outlet are the most affected areas due to the sediment erosion. Several attempts have been made in the past to minimize the losses due to the sediment erosion in the hydraulic turbines. However, the problem has not been solved satisfactorily. A dry clearance gap between the guide vanes and the cover plates usually exists in the Francis turbines, fromthe design. The deflection of cover plates and the erosion of the components causes the clearance gap to increase by multiple times of its design value. Inherit pressure difference between guide vane surfaces forces a leakage flow from the increased clearance gap. A systematic study of the characteristics of the leakage flow, and its effects on the flow conditions inside the Francis turbine distributor has not been reported yet. Such studies are necessary for the design optimization of the turbine components and to plan the effective maintenance schedules for repairing the eroded turbine parts. The main objective of this work is to study the effects of sediment erosion in hydro turbines, with the focus on the flow around the guide vanes of a low specific speed Francis turbine. Experimental investigations of the characteristics of leakage flow from the increased clearance gap between eroded guide vanes and cover plates, has been the focus of this study. A one-guide vane cascade has been developed to represent the flow inside a low specific speed Francis turbine distributor. Cases with five different sizes of clearance gap are investigated for the guide vane shaped with a symmetric profile. Particle Image Velocimetry techniques are applied for the flow measurement. All experiments have been carried out at the Waterpower Laboratory of Norwegian University of Science and Technology. Flow velocity exceeding 35 m/s, at the runner inlet of Francis turbine, is reported for the first time from such experimental studies. The results show that, that the clearance gap up to 0.5 mm does not have significant effects on the flow parameters and hence can be accepted as the maximum limit. The leakage flow, with clearance gap more than 1 mm, is found to change the velocity components at the runner inlet significantly. The case with the clearance gap of 2 mm is found to have the highest effects on the flow velocities and is considered as the critical size. The total crosswise leakage flow, from the critical clearance gap, is measured to be more than 1% of the main flow. As the consequence of the leakage flow, the relative velocity at the runner inlet is found to increase locally up to three times from its design value. This local increase in relative velocity is identified as the cause to have severe erosion at the runner hub in the sediment-laden projects. The leakage flow also changes the pressure distribution around guide vane, causing the torque on the guide vane shaft to increase up to 28%. Further investigation of the propagation of the leakage flow into the turbine runner, and its effects on the runner’s performance is necessary. Alternative designs of guide vane geometry, to minimize the differential pressure across is recommended as the future works.nb_NO
dc.language.isoengnb_NO
dc.publisherNTNUnb_NO
dc.relation.ispartofseriesDoctoral theses at NTNU;2016:260
dc.relation.haspartPaper A: Thapa, Biraj Singh; Dahlhaug, Ole Gunnar; Thapa, Bhola. Sediment erosion in hydro turbines and its effect on the flow around guide vanes of Francis turbine. Renewable & Sustainable Energy Reviews 2015 ;Volum 49. s. 1100-1113 http://dx.doi.org/10.1016/j.rser.2015.04.178
dc.relation.haspartPaper B: Thapa, Biraj Singh; Trivedi, Chirag; Dahlhaug, Ole Gunnar. Design and development of guide vane cascade for a low speed number Francis turbine. Journal of Hydrodynamics 2016 ;Volum 28.(4) s. 676-689 http://dx.doi.org/10.1016/S1001-6058(16)60648-0
dc.relation.haspartPaper C: Flow measurements in the distributor of Francis turbine: A PIV approach
dc.relation.haspartPaper D: Sediment erosion induced leakage flow from guide vane clearance gap in a Francis turbine. Renewable Energy - http://dx.doi.org/10.1016/j.renene.2017.01.045 © 2017. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/
dc.relation.haspartPaper E: Effects of sediment erosion in guide vanes of Francis turbine
dc.relation.haspartPaper F: Biraj Singh Thapa; Ole Gunnar Dahlhaug; Bhola Thapa. Flow field measurement in guide vane cascade of a high head Francis turbine. In Proceedings of 6th International Conference on Water Resources and Hydropower Development in Asia, 2016
dc.relation.haspartPaper G: Thapa, Biraj Singh; Dahlhaug, Ole Gunnar; Thapa, Bhola. Velocity and pressure measurements in guide vane clearance gap of a low specific speed Francis turbine. IOP Conference Series: Earth and Environment 2016 ;Volum 49. http://dx.doi.org/10.1088/1755-1315/49/6/062019 Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Published under licence by IOP Publishing Ltd
dc.titleEffects of sediment erosion in guide vanes of Francis turbinesnb_NO
dc.typeDoctoral thesisnb_NO
dc.subject.nsiVDP::Technology: 500::Environmental engineering: 610nb_NO


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