Wind energy, together with other renewable energy sources, are expected to grow substantially in the coming decades and play a key role in mitigating climate change and achieving energy sustainability. One of the main challenges in optimizing the design, operation, control, and grid integration of wind farms is the prediction of their performance, owing to the complex multiscale two-way interactions between wind farms and the turbulent atmospheric boundary layer (ABL). From a fluid mechanical perspective, these interactions are complicated by the high Reynolds number of the ABL flow, its inherent unsteadiness due to the diurnal cycle and synoptic-forcing variability, the ubiquitous nature of thermal effects, and the heterogeneity of the terrain. Particularly important is the effect of ABL turbulence on wind-turbine wake flows and their superposition, as they are responsible for considerable turbine power losses and fatigue loads in wind farms. These flow interactions affect, in turn, the structure of the ABL and the turbulent fluxes of momentum and scalars. This review summarizes recent experimental, computational, and theoretical research efforts that have contributed to improving our understanding and ability to predict the interactions of ABL flow with wind turbines and wind farms.

https://link.springer.com/content/pdf/10.1007/s10546-019-00473-0.pdf

Wind-Turbine and Wind-Farm Flows: A Review

Doppler wind LiDAR (Light Detection And Ranging) makes use of the principle of optical Doppler shift between the reference and backscattered radiations to measure radial velocities at distances up to several kilometers above the ground. Such instruments promise some advantages, including its large scan volume, movability and provision of 3-dimensional wind measurements, as well as its relatively higher temporal and spatial resolution comparing with other measurement devices. In recent decades, Doppler LiDARs developed by scientific institutes and commercial companies have been well adopted in several real-life applications. Doppler LiDARs are installed in about a dozen airports to study aircraft-induced vortices and detect wind shears. In the wind energy industry, the Doppler LiDAR technique provides a promising alternative to in-situ techniques in wind energy assessment, turbine wake analysis and turbine control. Doppler LiDARs have also been applied in meteorological studies, such as observing boundary layers and tracking tropical cyclones. These applications demonstrate the capability of Doppler LiDARs for measuring backscatter coefficients and wind profiles. In addition, Doppler LiDAR measurements show considerable potential for validating and improving numerical models. It is expected that future development of the Doppler LiDAR technique and data processing algorithms will provide accurate measurements with high spatial and temporal resolutions under different environmental conditions.

A review of progress and applications of pulsed doppler wind LiDARs

Temperature and humidity profiles in the atmospheric boundary layer (i.e., from the surface to 3 km) can be retrieved from ground-based spectral infrared observations made by the atmospheric emitted radiance interferometer (AERI) at high temporal and moderate vertical resolution. However, the retrieval is an ill-posed problem, and thus there are multiple thermodynamic solutions that might satisfy the observed radiances. Previous work developed a physical-iterative method called AERIoe that retrieved temperature and water vapor mixing ratio profiles from these radiance observations in both clear and cloudy conditions. The AERIoe algorithm was modified to enforce two physical constraints, namely that the derived relative humidity must be less than 100% and that the potential temperature must be monotonically increasing with height above some thin potentially subadiabatic layer after each iteration. Furthermore, additional observations including in situ surface meteorology, numerical weather prediction model output, microwave brightness temperatures, and partial profiles of water vapor from a Raman lidar were incorporated into the observation vector of the retrieval along with the infrared radiance observations. The addition of these new observations markedly improved the accuracy of the temperature profiles, especially above 2 km, and the water vapor profiles relative to radiosondes. These improvements are seen using cases from the tropics, mid-latitudes, and Arctic.

/pdf/improvements-to-the-aerioe-thermodynamic-profile-retrieval-2yao927a1y.pdf

Improvements to the AERIoe Thermodynamic Profile Retrieval Algorithm

We review developments in the field of boundary-layer flow over complex topography, focussing on the period from 1970 to the present day. The review follows two parallel strands: the impact of hills on flow in the atmospheric boundary layer and gravity-driven flows on hill slopes initiated by heating or cooling of the surface. For each strand we consider the understanding that has resulted from analytic theory before moving to more realistic numerical computation, initially using turbulence closure models and, more recently, eddy-resolving schemes. Next we review the field experiments and the physical models that have contributed to present understanding in both strands. For the period 1970–2000 with hindsight we can link major advances in theory and modelling to the key papers that announced them, but for the last two decades we have cast the net wider to ensure that we have not missed steps that eventually will be seen as critical. Two important new themes are given prominence in the 2000–2020 period. The first is flow over hills covered with tall plant canopies. The presence of a canopy changes the flow in important ways both when the flow is nearly neutral and also when it is stably stratified, forming a link between our two main strands.
The second is the use of eddy-resolving models as vehicles to bring together hill flows and gravity-driven flows in a unified description of complex terrain meteorology.

/pdf/boundary-layer-flow-over-complex-topography-wwg3maq932.pdf

Boundary-Layer Flow Over Complex Topography

With global energy consumption increasing, a shift to renewable energy resources is critical for sustainable energy development. Wind energy has emerged as one of the most promising sustainable and renewable energy resources, with the ability to contribute to the world's energy demand significantly. Although wind is a renewable and generally inexpensive energy source, the amount of electricity available varies depending on wind conditions (e.g., speed and direction). As a result, it is critical to learn how to harvest wind energy more effectively and reliably. Furthermore, most newly constructed wind turbines were built onshore, demonstrating that the consequences of varied terrains are becoming increasingly crucial to the wind-energy field. As a result, before wind farm construction, the investment corporation must evaluate wind conditions and wind turbine wake behavior in the natural wind park site (which may include complex terrain). These investigations can be made using field measurements, laboratory experiments, or numerical simulations. In light of this trend, the present work contributes additional insights into the flow situation occurring around onshore wind turbines in the presence of different complex terrain types—Atmospheric Boundary Layer (ABL) wind profile and turbine wake recovery over hilly and forested terrains. On the contrary, there is still limited knowledge on some issues, such as how a wind farm operates in complex terrain. 

A Review of Wind Turbines in Complex Terrain

A grand challenge from the wind energy industry is to provide reliable forecasts on mountain winds several hours in advance at microscale (∼100 m) resolution. This requires better microscal...

/pdf/the-perdigao-peering-into-microscale-details-of-mountain-55lcnz4r74.pdf

The Perdigão: Peering into Microscale Details of Mountain Winds

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The Perdigão: Peering into Microscale Details of Mountain Winds