Big wind power: open questions for turbulence research

The growing deployment scale of wind power is pushing the technology into areas where a number of science uncertainties still exist, including fluid dynamics aspects. In particular, turbulence plays a vital role in interactions between wind turbine blades, wind turbine wakes, wind farm wakes and the atmospheric boundary layer. In this presentation, we briefly review relevant aspects of various research questions that have been articulated recently (J. Turbulence vol. 20, 2-20 (2019)). These questions touch upon the need for better analytical, synthetic and reduced order models of turbulence, better model coupling methods to e.g. couple Large Eddy Simulations to meso- and global scale models, and basic understanding of flow phenomena governing kinetic energy entrainment and limiting power density. We will focus discussion on the latter question, specifically reviewing the budget of mean flow kinetic energy, i.e. the budget of the resource of interest, and the often opposing trends associated with turbulence. These opposing trends are reflected in increased turbulent mixing which tends to mitigate the wake strength downstream and thus increase wind energy production while also increasing turbulent dissipation of mean kinetic energy, which is associated with increased overall losses. Progress along the articulated research directions are needed for robust continued improvements in wind energy and widespread implementation.