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Tip-vortex instabilities of two in-line wind turbines
KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre. Instituto Tecnológico de Aeronáutica, Praça Marechal Eduardo Gomes, 50, Vila das Acácias, São Josédos Campos SP, 12228-900, Brazil.
KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre.
KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre.ORCID iD: 0000-0002-5913-5431
KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre.ORCID iD: 0000-0001-7864-3071
2019 (English)In: Wake Conference 201922–24 May 2019, Visby, Sweden, Institute of Physics Publishing (IOPP), 2019, Vol. 1256, no 1, article id 012015Conference paper, Published paper (Refereed)
Abstract [en]

The hydrodynamic stability of a vortex system behind two in-line wind turbines operating at low tip-speed ratios is investigated using the actuator-line method in conjunction with the spectral-element flow solver Nek5000. To this end, a simplified setup with two identical wind turbine geometries rotating at the same tip-speed ratio is simulated and compared with a single turbine wake. Using the rotating frame of reference, a steady solution is obtained, which serves as a base state to study the growth mechanisms of induced perturbations to the system. It is shown that, already in the steady state, the tip vortices of the two turbines interact with each other, exhibiting the so-called overtaking phenomenon. Hereby, the tip vortices of the upstream turbine overtake those of the downstream turbine repeatedly. By applying targeted harmonic excitations at the upstream turbine's blade tips a variety of modes are excited and grow with downstream distance. Dynamic mode decomposition of this perturbed flow field showed that the unstable out-of-phase mode is dominant, both with and without the presence of the second turbine. The perturbations of the upstream turbine's helical vortex system led to the destabilization of the tip vortices shed by the downstream turbine. Two distinct mechanisms were observed: for certain frequencies the downstream turbine's vortices oscillate in phase with the vortex system of the upstream turbine while for other frequencies a clear out-of-phase behaviour is observed. Further, short-wave instabilities were shown to grow in the numerical simulations, similar to existing experimental studies [1].

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2019. Vol. 1256, no 1, article id 012015
Series
Journal of Physics: Conference Series, ISSN 1742-6588
National Category
Mechanical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-262574DOI: 10.1088/1742-6596/1256/1/012015Scopus ID: 2-s2.0-85070017009OAI: oai:DiVA.org:kth-262574DiVA, id: diva2:1365322
Conference
Wake Conference 2019; Uppsala University's Gotland Campus, Visby; Sweden; 22 May 2019 through 24 May 2019
Note

QC 20191024

Available from: 2019-10-24 Created: 2019-10-24 Last updated: 2019-10-24Bibliographically approved

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Kleine, VitorKleusberg, ElektraHanifi, ArdeshirHenningson, Dan S.

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