Abstract
In this work a technique capable to investigate the near-wake stability properties of a wind turbine immersed in the atmospheric boundary layer is presented. Specifically, a 2D local spatial stability analysis is developed in order to take into account typical flow features of real operating wind turbines, such as the presence of the atmospheric boundary layer and the turbulence heterogeneity of the oncoming wind. This stability analysis can be generally applied on either experimental measurements or numerical data. In this paper it was carried out on wind tunnel experiments, for which a downscaled wind turbine is immersed in a turbulent boundary layer. Through spatial stability analysis, the dominant mode in the near wake, i.e. the most amplified one, is characterized and its frequency matches the hub-vortex instability frequency measured in the wind tunnel. As in the case of [10], where an axisymmetric wake condition was investigated, the hub-vortex instability results in a single-helical mode.
Highlights
In the wake of wind turbines two main vorticity structures are typically observed: the helicoidal tip vortices and the hub vortex
The method is based on the triple decomposition of the flow field, where an equation describing the dynamics of the coherent perturbations on the timeaveraged flow and taking into account the turbulent diffusion is provided
At a given streamwise position in the wake, x, both y and z directions are discretized by using Chebyshev polynomials and the spatial amplification of perturbations as a function of the frequency are computed
Summary
- The effect of the number of blades on wind turbine wake - a comparison between 2and 3-bladed rotors Franz Mühle, Muyiwa S Adaramola and Lars Sretran. - Identification and quantification of vortical structures in wind turbine wakes for operational wake modeling Y Marichal, I De Visscher, P Chatelain et al. - Wind turbine wakes in forest and neutral plane wall boundary layer large-eddy simulations Josef Schröttle, Zbigniew Piotrowski, Thomas Gerz et al. This content was downloaded from IP address 131.114.71.138 on 09/02/2021 at 11:21. Instability of wind turbine wakes immersed in the atmospheric boundary layer Francesco Viola, Giacomo Valerio Iungo, Simone Camarri, Fernando Porte-Agel and Francois Gallaire
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