An experimental study on wake evolution and trailing vortex instabilities

Authors: Odemark, Y., Fransson, J. H. M.
Document Type: Conference
Pubstate: Published
Journal: Proceedings of Wake Conference, Visby, June 8-10 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. The present work aims at developing an increased understanding of the behaviour of turbine wakes, with special regard to wake evolution and the stability of the trailing vortices. The evolution of the wake behind a small-scale model turbine was investigated experimentally in the Minimum Turbulence Level (MTL) wind tunnel at the Royal Institute of Technology (KTH), by performing velocity measurements with hot-wire anemometry (HWA). The set-up was monitored by also measuring the thrust, power output and rotational frequency of the model. The width and extension of the wake were measured for different free-stream velocities and different tip speed ratios, and compared to previous measurements. The stability of the trailing vortices was studied by applying small disturbances at the end of the nacelle, introduced through two orifices perpendicular to the main flow. This was done with a high-pressure accumulator tank and two fast-switching valves, with the possibility to trigger both varicose and sinusoidal modes. The results for different disturbance frequencies as well as the evolution of the vortices will be presented.