Although wind turbines have been well studied from a blade aerodynamics perspective, the interactions among these massive structures and the atmospheric turbulent boundary layer (ATBL) are still not understood in detail. It is important to understand such interactions in order to maximize the energy that can be extracted from the available wind resource. Past investigations have determined that wind turbines that operate within an array can display a significant power generation loss, when compared to a freestanding wind turbine. Thus, their ability to extract kinetic energy from the flow decreases due to complex interactions among them, the terrain topography and the atmospheric boundary layer.

In order to improve the understanding of the vertical transport of momentum and kinetic energy across a boundary layer flow with wind turbines, wind-tunnel experiments were performed to include a scaled down wind farm of 3x5. Particle-image-velocity measurements in a volume surrounding a target wind turbine are used to compute mean velocity and turbulence properties averaged on horizontal planes. The impact of vertical transport of kinetic energy due to turbulence and mean flow correlations is quantified. It is found that the fluxes of kinetic energy associated with the Reynolds shear stresses are of the same order of magnitude as the power extracted by the wind turbines, highlighting the importance of vertical transport of turbulence in the boundary layer and thus in wind farms.

The concept of coherent transfers of energy is employed here as means to uncover the scales responsible for the entrainment of mean kinetic energy into the array. The major contributions to the MKE entrainment are achieved by large-scale motions associated with sums of the Reynolds shear stress, (idiosyncratic) modes. The sum of the first 9 modes yield 54% of the total energy entrainment, with scales given by L ~ 13D associated with this sum. From these results, it is clear that scales of the order of the total wind farm size are those which are critical in determining how much power can be extracted from the atmospheric boundary layer. In addition, during this seminar it will be shown that dispersive stresses are also important in the energy entrainment and dissipation in wind arrays with complex topography and where proximity between turbines exists.

Short Bio

Luciano Castillo is the Don-Kay-Clay Cash Distinguished Engineering Chair in Wind Energy and the executive Director/President of the National Wind Resource Center (NWRC) at Texas Tech University. After spending 12 years at Rensselaer Polytechnic Institute. In 2011 he joined the ME department at TTU. His research in turbulence using experimental techniques, direct numerical simulations and multi-scale asymptotic analysis has injected new ideas in turbulent boundary layers and our understanding of initial conditions on large scale turbulence, particularly on wind energy. Some of his awards include: the NASA Faculty Fellowship, the Martin Luther King Faculty Award, and the Robert T. Knapp Award on complex flows from the ASME among others. He published over 100 articles including a seminal paper on turbulent boundary layers and scaling laws. He is currently, leading various initiatives on wind energy in the USA and Europe.

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