• Energy Research

This work addresses specifically the setup and evaluation of the multiscale large-eddy simulation (LES) version of the Weather Research and Forecasting Model (WRF-LES). To this end, the wind fields simulated by WRF-LES are examined at two sites that depict very different climate and orographic environments: the Cabauw Experimental Site for Atmospheric Research in the Netherlands and the Alaiz test site, located in a mountainous area in northeast Spain, which has been part of the New European Wind Atlas (NEWA) experimental campaigns. The site���s selection lines up with the efforts carried out by the International Energy Agency (IEA) Task 31 to set up a wind flow modelling and evaluation framework. So, we take advantage of their curated experimental database, particularly from two of their carefully prepared benchmarks used for this evaluation: GABLS3 and ALEX17, conducted at Cabauw and Alaiz, respectively. These benchmarks analyze weather episodes of one-to-few days duration to assess the model���s accuracy to simulate diurnal cycles with strong mesoscale components in flat and complex terrain environments. Additionally, we���ve explored the sensitivity to the following model���s setup. 1) Domain configuration, 2) Planetary Boundary Layer (PBL) schemes, and 3) Subfilter-scale (SFS) models set at the LES-resolved numerical domains.

Abstract A procedure for testing and evaluation of remote sensing instruments that makes use of two test sites in flat and complex terrain is presented. To illustrate the method, a system intercomparison experiment is presented involving one sodar and two lidars (pulsed and continuous-wave). The wind profilers are benchmarked with respect to reference cup anemometer and other mast-based instrumentation. The evaluation procedure comprises three steps: single-point regression, ensemble-averaged profile analysis and performance matrix summary. Apart from the influence of the terrain complexity on the flow field, it is also investigated the influence of the background atmospheric stability by classifying the results with the Richardson number in flat terrain and the Froude number in complex terrain. The result is a thorough field calibration of the instruments for a wide range of terrain-flow conditions fit for the purpose of conducting wind resource assessment campaigns.

The increasing size of wind turbines, with rotors already spanning more than 150 m diameter and hub heights above 100 m, requires proper modeling of the atmospheric boundary layer (ABL) from the surface to the free atmosphere. Furthermore, large wind farm arrays create their own boundary layer structure with unique physics. This poses significant challenges to traditional wind engineering models that rely on surface‐layer theories and engineering wind farm models to simulate the flow in and around wind farms. However, adopting an ABL approach offers the opportunity to better integrate wind farm design tools and meteorological models. The challenge is how to build the bridge between atmospheric and wind engineering model communities and how to establish a comprehensive evaluation process that identifies relevant physical phenomena for wind energy applications with modeling and experimental requirements. A framework for model verification, validation, and uncertainty quantification is established to guide this process by a systematic evaluation of the modeling system at increasing levels of complexity. In terms of atmospheric physics, ‘building the bridge’ means developing models for the so‐called ‘terra incognita,’ a term used to designate the turbulent scales that transition from mesoscale to microscale. This range of scales within atmospheric research deals with the transition from parameterized to resolved turbulence and the improvement of surface boundary‐layer parameterizations. The coupling of meteorological and wind engineering flow models and the definition of a formal model evaluation methodology, is a strong area of research for the next generation of wind conditions assessment and wind farm and wind turbine design tools. Some fundamental challenges are identified in order to guide future research in this area. WIREs Energy Environ 2017, 6:e214. doi: 10.1002/wene.214This article is categorized under: Wind Power > Climate and Environment Energy and Climate > Climate and Environment Energy Policy and Planning > Climate and Environment

Presentation at the Torque Conference, 6 October 2016, Munich. The associated paper can be found at: https://iopscience.iop.org/article/10.1088/1742-6596/753/3/032024 Abstract The third GEWEX Atmospheric Boundary Layer Studies (GABLS3) model intercomparison study, around the Cabauw met tower in the Netherlands, is revisited as a benchmark for wind energy atmospheric boundary layer (ABL) models. The case was originally developed by the boundary layer meteorology community, interested in analysing the performance of single-column and large-eddy simulation atmospheric models dealing with a diurnal cycle leading to the development of a nocturnal low-level jet. The case addresses fundamental questions related to the definition of the large-scale forcing, the interaction of the ABL with the surface and the evaluation of model results with observations. The characterization of mesoscale forcing for asynchronous microscale modelling of the ABL is discussed based on momentum budget analysis of WRF simulations. Then a single-column model is used to demonstrate the added value of incorporating different forcing mechanisms in microscale models. The simulations are evaluated in terms of wind energy quantities of interest.

This report ALEX17, the acronym for ALaiz EXperiment 2017, is the last full-scale experiment within the NEWA (New European Wind Atlas) project, whose primary objective is to create a wind atlas of Europe that includes the state-of-the-art in modelling the wind resource, as well as the creation of a comprehensive database. ALEX17 aims to present a utility-scale measurements campaign to characterize the wind flow in complex terrain, through a combination of measurement technologies. Having finalized the measurements campaign and processed all the information, the wind flow in the area of study can be characterized for different weather conditions. In addition, the experimental data will be able to validate the reliability of numeric simulation models of wind flow in complex terrain, in order to reduce uncertainties when evaluating the wind resource.

This dataset has been extracted from Letau (1950) to verify ABL models in neutral conditions.

Abstract. Atmospheric stability has a significant effect on wind shear and turbulence intensity, and these variables, in turn, have a direct impact on wind power production and loads on wind turbines. It is therefore important to know how to characterize atmospheric stability in order to make better energy yield estimation in a wind farm. Based on research grade meteorological mast at Alaiz (CENER's Test Site in Navarre, Spain) named MP5, this work compares and evaluates different instrument set-ups and methodologies for stability characterization. The Obukhov parameter ζ = z/L, which can be measured locally with the use of a sonic anemometer, and bulk Richardson number have been studied. The methods are examined considering their theoretical background, implementation complexity, instrumentation requirements, and practical use in connection with wind energy applications. Bulk Richardson number, which is based on one height wind speed measurement and two temperature measurements, is sometimes calculated using values from any two temperature levels without taking into account that one of the measurements would be representative of surface conditions. With the data available in MP5, it will be shown how this approximation is not correct to obtain an adequate stability characterization.