dc.contributor.author | Eliassen, Lene | |
dc.date.accessioned | 2015-06-01T08:51:00Z | |
dc.date.available | 2015-06-01T08:51:00Z | |
dc.date.issued | 2015-03-13 | |
dc.identifier.citation | Aerodynamic loads on a wind turbine rotor in axial motion by Lene Eliassen, Stavanger : University of Stavanger, 2015 (PhD thesis UiS, no. 245) | nb_NO |
dc.identifier.isbn | 978-82-7644-593-0 | |
dc.identifier.issn | 1890-1387 | |
dc.identifier.uri | http://hdl.handle.net/11250/284344 | |
dc.description | PhD thesis in Offshore technology | nb_NO |
dc.description.abstract | This study investigates the unsteady aerodynamics of attached flow on
a two-dimensional airfoil. The unsteady aerodynamics introduces aerodynamic
damping of the offshore wind turbine structure and is thus important
for the turbine structural integrity. This includes an impact on
the fatigue damage of the structure and, consequently, an effect on the
total cost of energy.
Unsteady aerodynamics can be studied using a variety of methods. In
this thesis, a panel vortex method was developed to estimate the aerodynamic
forces. This method is based on potential theory, which can’t
account for the viscosity in the fluid. Consequently, dynamic stall, which
is an important unsteady aerodynamic effect, can not be modeled, and
we are limited to attached flow conditions.
Despite this limitation, the vortex method is in some situation the
preferred option when investigating unsteady aerodynamics. The vortex
method has the advantage of considering the wake history in the estimation
of the aerodynamic forces. Using the panel vortex method developed
in this study, one is not dependent on look-up tables since the aerodynamic
loads are calculated by direct modelling of flow conditions on an
airfoil of a given geometry. However, the computational time of the vortex
method is long and is therefore often not used.
There is a possibility to reduce the computational time of the vortex
method. By using a graphic processing unit, it is demonstrated how the
computational time can be reduced for a two-dimensional panel vortex
code. A significant reduction in computational time can be achieved
for the simulation, depending on the number of vortex elements in the
analysis. For a low amount of vortex elements, the computation is faster
on a central processing unit, CPU.
The panel vortex method is used to investigate the motion induced
aerodynamic loads on an offshore wind turbine. Studying the flow conditions
on an airfoil oscillating in plunge motion at frequencies similar
to the eigenfrequencies for a floating spar type wind turbine, the aerodynamic
damping for eigenmodes represented is estimated. Including the
neighbouring airfoils and their wakes in the analysis has a relatively large
effect on the estimated aerodynamic damping. The aerodynamic damping
is reduced when the period of the oscillating airfoil is equal to the time
it takes for one airfoil to travel from its original position to the neighbouring
airfoil’s original position. One example where this can occur is if
the eigenfrequency of the tower is equal to the blade passing frequency.
This effect has previously been studied by other researchers, but mostly
for helicopter rotors.
The change in the wind-structure interaction effects is studied with regards
to the fatigue damage of the tower using a single degree of freedom
model. Comparing the fatigue damage results using different computational
methods to estimate the aerodynamic forces can be useful when
evaluating the effect of the aerodynamic model chosen on the cost. This
study only focuses on one unsteady plunging motion, and is therefore
limited. It is found that the unsteady aerodynamic models that are most
commonly used may overestimate the damping, and thus estimate a too
low fatigue damage. This will have a negative impact on the cost if the
wind turbine fails. | nb_NO |
dc.language.iso | eng | nb_NO |
dc.publisher | University of Stavanger, Norway | nb_NO |
dc.relation.ispartofseries | PhD thesis UiS;245 | |
dc.rights | Copyright the author, all right reserved | |
dc.rights | Navngivelse 3.0 Norge | * |
dc.rights.uri | http://creativecommons.org/licenses/by/3.0/no/ | * |
dc.subject | offshore teknologi | nb_NO |
dc.subject | vindturbiner | nb_NO |
dc.subject | vindpåkjenning | nb_NO |
dc.subject | virvelkoder | nb_NO |
dc.title | Aerodynamic loads on a wind turbine rotor in axial motion | nb_NO |
dc.type | Doctoral thesis | nb_NO |
dc.subject.nsi | VDP::Technology: 500::Materials science and engineering: 520 | nb_NO |