1 Department of Mechanical Engineering, Technical University of Denmark2 Fluid Mechanics, Department of Mechanical Engineering, Technical University of Denmark3 Department of Wind Energy, Technical University of Denmark
The present thesis deals with the study of the rotational effects on the laminar-turbulent transition on wind turbine blades. Linear stability theory is used to formulate the stability equations that include the effect of rotation. The mean flow required as an input to stability computations is obtained by a similarity transformation technique. This approach allows to transform the boundary layer equations that have included the effect of the Coriolis and centrifugal forces into a set of couple partial differential equations, that are more convenient to solve numerically. The solution have been parametrized and adapted to an wind turbine rotor geometry. The blade is resolved in radial sections along which calculations are performed. The obtained mean flow is classified according to the parameters used on the rotating configuration, geometry and operational conditions. The stability diagrams have been obtained by solving the stability equations as an eigenvalue problem. The Keller box Scheme that is second order accurate was used as a numerical method. Have found to be stable and effective in terms of computing time. The solution of the eigenvalue problem provide connection between the parameters used to define the resultant wave magnitude and direction. The propagation of disturbances in the boundary layers in three dimensional flows is relatively a complicated phenomena. The report discusses the available methods and techniques used to predict the transition location. Some common wind turbine airfoils are selected to performe parametrical studies with rotational effects. Finally a wind turbine rotor is used for comparison with transition experiments. The relative motion between the flow and the blade geometry defines the response of the flow to disturbances. Have been found that flow on the suction side of the blade has a stabilizating effect, while on the region from the stagnation point to the rotor plane has a destabilizating effect on the boundary layer. The tendency is that rotational effect stabilize the boundary layer on the wind turbine blade.