An experimental study on tip vortex instabilities and breakdown

Authors: Odemark, Y., Fransson, J. H. M.
Document Type: Conference
Pubstate: Published
Journal: Svenska mekanikdagarna, Göteborg, June 13-15 2011
Year: 2011


The production losses and inhomogeneous loads of wind power turbines placed in the wake of another turbine is a well-known problem when building new wind power farms, and a subject of intensive research. In order to maximize the power output and extend the life time of a turbine, knowledge about the evolution and extension of the wakes is crucial. In the present study, the evolution of the wake behind a small-scale model turbine is investigated experimentally in the Minimum Turbulence Level (MTL) wind tunnel at the Royal Institute of Technology (KTH). Velocity measurements with hot-wire anemometry are performed in the wake of the model, in order to characterize the wake with regard to the extent in space and the location of the tip vortex breakdown. The width and extension of the wake are measured for different free-stream velocities and different tip speed ratios, and compared to previous measurements. Special consideration is given to the evolution of the tip and hub vortices and the location of their breakdown. The stability of these vortices are studied by applying sinusoidal disturbances of different frequencies at the end of the nacelle. Results for different frequencies as well as the resulting power output curves will be presented.