Meyer Forsting, Alexander Raul

En vindmølle opbremser vinden foran sig ved at udtrække kinetisk energi fra luften. Opbremsningen er størst i rotorplanet mens den er ubetydelig for opstrøms afstande større end 5 rotor radier (R). Området foran rotoren hvor opbremsningen er signifikant kaldes for induktionszonen. Vindha-stighedsmålinger mere end 5R opstrøms vil således ikke være influeret af vindmøllen. Imidlertid vil vindhastigheden her til dels være dekorreleret med den vind der faktisk rammer vindmøllen, specielt i de tilfælde hvor den er placeret i en vindmøllepark eller i komplekst terræn. For store vindmøller vil denne dekorrelering være endnu mere udtalt. Det er dog nødvendigt at have et eksakt mål af den tilgængelige vindhastighed for at kunne evaluere en vindmølles ydeevne. Dekorreleringen kan mindskes ved at måle tættere på rotoren, men dette vil kræve en bedre forståelse af induktionszonen således at målingerne kan korrigeres for opbremsnin-gen.Formålet med den foreliggende afhandling er derfor at studere induk-tionszonen og dens afhængighed af vindmøllen eller de ydre omgivel-ser. De fleste resultater præsenteret i afhandlingen er fundet vha. Navier-Stokes simuleringer (CFD). Simuleringerne er blevet valideret ved at sam-menligne med lidarmålinger opstrøms en fuldskala vindmølle. I forbin-delse med valideringen blev der brugt en helt ny stokastisk validerings-metode kombineret med omfattende usikkerhedskvantificering som viser vigtigheden og fordelene ved at inkludere usikkerhederne i validering af CFD modeller.Induktionszonen for en isoleret vindmølle er kun lidt følsom overfor møl-lens specifikke rotor design og de eksterne vindforhold (vindgradient, turbulens etc.), hvorimod den er meget sensitiv overfor ændringer i rotor thrust-koefficienten. Påbaggrund af denne viden er en hurtig og simpel semi-empirisk model blevet præsenteret som kan forudsige hastigheds-opbremsningen opstrøms en enkeltstående mølle. Situationer med kom-plekst terræn eller tætstående møller er dog mere krævende at forudsige.Det bliver vist at den indkommende vind til en række af møller afviger fra den der eksisterer for en enkeltstående mølle ved bl.a. at være mere afhængig af vindretningen. Denne observation udfordrer den nuværende måde hvorpå man evaluerer vindmøllers ydeevne, da dette ofte foregår på flade områder hvor møllerne står på række. From the first time I met my supervisor Niels Troldborg, I knew he is someone I would like to work with the next couple of years. I am truly grateful for his continued support throughout the three years - not only at a work level. His motivation is capturing, he is extraordinarily humble and invested a lot of time in me. He never tried to dictate an agenda, but instead knew exactly how to nudge me in the right direction. Thank you so much Niels! I would also express my gratitude to my co-supervisor Andreas Bechmann for his support regarding complex terrain flows and simulations. He was extremely approachable at all times. Many thanks also to Prof. Christian Masson for hosting me at ÉTS and essentially be-coming my supervisor for a few months. Generally, everyone that I was involved with in the UniTTe project was tremendously helpful and happy to support me - in particular Antoine Borraccino, Ameya Sathe, Nikolas Angelou and Andrea Vignaroli. Rozenn Wagner was a great project leader to have. I also need to thank my fellow PhD students and colleagues at DTU Wind - in particular Mac Gaunaa, Paul van der Laan and Niels Sørensen - and in Montréal for creating such a great work atmosphere. I sincerely enjoyed collaborating with my PhD colleagues and friends Juan-Pablo Murcia Leon, Emmanuel Branlard and Jörn Nathan (ÉTS) and am extremely grateful for incorporating me in their work. A big thank you also to my footballing friends in Copenhagen and those at my home airport EDWN in Klausheide, especially to my gliding club LSV Lingen, for allowing me to forget about my PhD every now and then. Finally, I would like to thank my parents, brother and grandparents on both sides of the Atlantic for their moral support. And of course thank you Bryony for coming to Copenhagen and making life so much better.A wind turbine decelerates the wind in front of its rotor by extracting kinetic energy. The wind speed reduction is maximal at the rotor and negligible more than five rotor radii upfront. By measuring wind speed this far from the rotor, the turbine’s performance is determined without any rotor bias. However, the measured wind speed decorrelates from the one interacting with the rotor especially in wind farms and mountainous terrain. This is exacerbated by the ever growing rotors, as the physical distance to the measurement location grows equally. Decorrelation is mitigated by measuring closer to the rotor, but requires exact knowledge of the flow deceleration to estimate the available, undis- turbed kinetic energy. Thus this thesis explores, mostly numerically, any wind turbine or environmental dependencies of this deceleration. The computational fluid dynamics model (CFD) employed is validated with velocity measurements from lidars upstream of an operational turbine. A new stochastic validation methodology in combination with extensive uncertainty quantification and propagation allows validating the CFD model under these realistic conditions for an area covering the majority of the decelerating flow upstream. This is the first validation of its kind and it demonstrates the advantage of including uncertainties in the process. The flow behaviour upstream of a single rotor is largely insensitive to specific rotor designs and operating conditions. In fact the rotor thrust coefficient is the single most significant parameter. Exploiting this singu- lar dependency, a fast semi-empirical model is devised that accurately predicts the velocity deficit upstream of a single turbine. Near-rotor mea-surements in combination with this model are able to retrieve the kinetic energy available to the turbine in flat terrain. Complex terrain and mul-tiple turbines are more demanding, though, as they enhance non-linearinteractions

Online Research Database In Technology

Modelling Wind Turbine Inflow: The Induction Zone

http://orbit.dtu.dk/ws/files/142549266/AMeyerForsting_PhD17.pdf

Modelling Wind Turbine Inflow: The Induction Zone

Abstract

Similar works

Full text

Available Versions

Online Research Database In Technology