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Coherent structures and rotational effects on the flow over spinners of horizontal axis wind turbines

Publikation: Qualifikations-/StudienabschlussarbeitDissertation

Autorschaft

  • Shy-Yea Lin

Details

OriginalspracheEnglisch
QualifikationDoktor der Ingenieurwissenschaften
Gradverleihende Hochschule
Betreut von
  • Jörg Reinhart Seume, Betreuer*in
Datum der Verleihung des Grades24 Juni 2016
ErscheinungsortHannover
PublikationsstatusVeröffentlicht - 2016

Abstract

Die dreidimensionalen Rotationseffekte, die die Vorhersagegenauigheit der Leistung von horizontalachsigen Windenergieanlagen senken, hängen mit den kohärenten Strukturen im Nabenbereich, speziell mit der Ablösung, zusammen. Das Verständnis der komplexen kohärenten Strukturen und der dreidimensionalen Rotationseffekte auf die Strömung im Nabenbereich
der horizontalachsigen Windenergieanlagen ist die Zielsetzung dieser Arbeit. Die Strömungsfelder zur Identifikation der kohärenten Strukturen und der 3D Rotationseffekte werden durch die Berechnungen der Reynolds-gemittelten Navier-Stokes Gleichungen ermittelt. Die komplexen kohärenten Strukturen, die von der viskosen Scherströmung behaftet sind, werden in dieser Arbeit durch verschiedene Methoden identifiziert. Die kohärenten Strukturen im Nabenbereich der Referenzanlage beinhalten den spiralförmigen Wurzelwirbel, den Hinterkantenwirbel, die Ablösung mit erheblicher radialer Geschwindigkeitskomponente, die Karman’sche Wirbelstraße, das gegenläufige Fußwirbelpaar, den Hufeisenwirbel und die langsame Nachlaufströmung hinter der Gondel. Der Zusammenhang des Ursprungs und der Entwicklung der spiralförmigen Wurzelwirbels mit der Zirkulation der Tragflügel wird veri-
fiziert. Die dominante Parameter, die für die 3D Rotationseffekte auf die anliegende und abgelöste Grenzschichten verantwortlich sind, werden durch die Größenordnungsanalyse abgeschätzt. Die Rotationseffekte auf die Referenzanlage haben den Anstieg des Auftriebsbeiwerts, den Abfall des Widerstandsbeiwerts und die erhebliche radiale Strömung der Ablösung zur Folge. Die erhebliche radiale Geschwindigkeitskomponente der Ablösung entsteht durch die Zentrifugalkräfte und ist vorhersagbar. Die Coriolis-Beschleunigung in Richtung der Sehnenlänge, die durch die radiale Geschwindigkeitskomponente der Ablösung induziert wird, steht mit einem Druckgradienten in Richtung der Sehnenlänge im Gleichgewicht. Der
Gradient des Druckbeiwerts in Richtung der Sehnenlänge der 3D rotierenden Rotorblätter stimmt mit der analytischen Korrelation, die in dieser Arbeit hergeleitet wurde, überein. Der genaue Ablösepunkt wird durch ein neues Kriterium, das auf Basis der Wandschubspannung definiert wurde, ermittelt. Die geringe Verschiebung des Ablösepunktes entweder in Richtung Hinter- oder Vorderkante des rotierenden Blattes zeigen die verschiedenen Einflüsse der
Berücksichtigung der Rotationseffekte auf die anliegende und abgelöste Grenzschichten.

Zitieren

Coherent structures and rotational effects on the flow over spinners of horizontal axis wind turbines. / Lin, Shy-Yea.
Hannover, 2016. 111 S.

Publikation: Qualifikations-/StudienabschlussarbeitDissertation

Lin, S-Y 2016, 'Coherent structures and rotational effects on the flow over spinners of horizontal axis wind turbines', Doktor der Ingenieurwissenschaften, Gottfried Wilhelm Leibniz Universität Hannover, Hannover. https://doi.org/10.15488/8735
Lin SY. Coherent structures and rotational effects on the flow over spinners of horizontal axis wind turbines. Hannover, 2016. 111 S. (Berichte aus dem Institut für Turbomaschinen und Fluid-Dynamik). doi: 10.15488/8735
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abstract = "Three-dimensional effects due to rotation which decrease the accuracy of predicting the wind turbine aerodynamic performance, are correlated with coherent structures near the blade roots, specifically with the flow separation. This study aims to give an insight into the complex coherent structures and the 3D rotational effects on the flow over spinners of horizontal axis wind turbines. The flow fields for the identification of the coherent structures and the 3Drotational effects are obtained by solving the Reynolds-averaged Navier-Stokes equations. The complex coherent structures, dominated by viscous shear layers are identified in this study by using various vortex detection methods. The coherent structures near the blade roots of the baseline wind turbine include helical root vortices, trailing edge vortices, flow separation with significant radial flows, von K{\'a}rm{\'a}n vortex streets, pairs of counter-rotating base vor-tices, horseshoe vortices, and a low-speed nacelle wake. The correlation between the helical root vortex and the blade-bound circulation is verified. The dominant sources responsible for the 3D rotational effect on attached and detached boundary layers are estimated by means of order of magnitude analysis. The 3D rotational effect on the baseline wind turbine results inlift augmentation, drag reduction, and significant radial flows in the flow separation region. The significant radial velocity components in the flow separation region are predictable, and substantially driven by the centrifugal acceleration. The Coriolis acceleration in the chordwise direction, induced by these significant radial velocity components in the bottom of the detached boundary layer, is balanced by a pressure gradient in the chordwise direction. This pressure gradient in the chordwise direction over the rotating blade agree well with the analytical expression derived in this study. The separation point is determined accurately in this study by a new criterion based on skin friction coefficients. The limited shift of separation points on the rotating blade, either towards the trailing edge or leading edge, indicates different effects due to rotation on the attached and detached boundary layers.",
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