Evaluation and performance prediction of a wind turbine blade
Date
2009-03
Authors
Pierce, Warrick Tait
Journal Title
Journal ISSN
Volume Title
Publisher
Stellenbosch : University of Stellenbosch
Abstract
The aerodynamic performance of an existing wind turbine blade optimised for low wind speed
conditions is investigated. The aerodynamic characteristics of four span locations are determined from
surface pressure measurements and wake surveys with a traversed five-hole probe performed in a low
speed wind tunnel for chord Reynolds numbers ranging from 360,000 - 640,000.
Two-dimensional modelling of the wind tunnel tests is performed with the commercial computational
fluid dynamics code FLUENT. The predictive accuracies of five eddy-viscosity turbulence models are
compared. The computational results are compared to each other and experimental data. It is found
that agreement between computational and experimental results varies with turbulence model. For
lower Reynolds numbers, the Transitional-SST turbulence model accurately predicted the presence of
laminar separation bubbles and was found to be superior to the fully turbulent models considered. This
highlighted the importance of transitional modelling at lower Reynolds numbers. With increasing angles
of attack the bubbles were found to move towards the leading edge and decrease in length. This was
validated with experimental data. For the tip blade section, computations implementing the k-ε
realizable turbulence model best predicted experimental data. The two-dimensional panel method
code, XFOIL, was found to be optimistic with significantly higher lift-to-drag ratios than measured.
Three-dimensional modelling of the rotating wind turbine rotor is performed with the commercial
computational fluid dynamics code NUMECA. The Coefficient of Power (Cp) predicted varies from 0.440
to 0.565 depending on the turbulence model. Sectional airfoil characteristics are extracted from these
computations and compared to two-dimensional airfoil characteristics. Separation was found to be
suppressed for the rotating case. A lower limit of 0.481 for Cp is proposed based on the experimental
data.
Description
Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2009.
Keywords
Wind turbines -- Aerodynamics, Dissertations -- Mechanical engineering, Theses -- Mechanical engineering