Schottler, Jannik and Bartl, Jan and Mühle, Franz and Sætran, Lars and Peinke, Joachim and Hölling, Michael
(2018)
Wind tunnel experiments on wind turbine wakes in yaw: redefining the wake width.
Wind energy science, 3 (1).
pp. 257-273.
ISSN 2366-7451
Abstract
This paper presents an investigation of wakes behind model wind turbines, including cases of yaw
misalignment. Two different turbines were used and their wakes are compared, isolating effects of boundary
conditions and turbine specifications. Laser Doppler anemometry was used to scan full planes of wakes normal to
the main flow direction, six rotor diameters downstream of the respective turbine. The wakes of both turbines are
compared in terms of the time-averaged main flow component, the turbulent kinetic energy and the distribution of
velocity increments. The shape of the velocity increments’ distributions is quantified by the shape parameter [lambda]2.
The results show that areas of strongly heavy-tailed distributed velocity increments surround the velocity deficits
in all cases examined. Thus, a wake is significantly wider when two-point statistics are included as opposed to
a description limited to one-point quantities. As non-Gaussian distributions of velocity increments affect loads
of downstream rotors, our findings impact the application of active wake steering through yaw misalignment as
well as wind farm layout optimizations and should therefore be considered in future wake studies, wind farm
layout and farm control approaches. Further, the velocity deficits behind both turbines are deformed to a kidneylike
curled shape during yaw misalignment, for which parameterization methods are introduced. Moreover, the
lateral wake deflection during yaw misalignment is investigated.
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