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Delegates are invited to meet and discuss with the poster presenters during the poster presentation sessions between 10:30-11:30 and 16:00-17:00 on Thursday, 19 November 2015.

Lead Session Chair:
Stephan Barth, ForWind - Center for Wind Energy Research, Germany
Alex Montornès Vortex, Spain
Co-authors:
Montornès Alex (1) F Casso Pau (1) Kosovic Branko (2)
(1) Vortex, Barcelona, Spain (2) NCAR, Boulder, United States

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Presenter's biography

Biographies are supplied directly by presenters at EWEA 2015 and are published here unedited

Alex Montornès joins academia and private industry. He has been working in the wind energy sector during the last five years, first as a wind forecasting specialist at AWS Truepower and now, as an atmospheric modeler researcher at Vortex. At the same time, he has undertaken a PhD research into the WRF-ARW physical parameterizations at the University of Barcelona. Despite his youth, he has contributed with several improvements within source code of the WRF-ARW as well as in peer-reviewed journals.


Poster

Poster Download poster (11.17 MB)

Abstract

Towards a seamless modeling chain

Introduction

An accurate and reliable wind resource assessment and forecasting tool requires a full, detailed and accurate understanding of the temporal and spatial distribution of the wind across the farm region. Today, the widely used approach in wind resource assessment as well as in wind forecasting consists in the combination between wind flow modeling and on-site measurements that are used to correct the model failures. The improvement of numerical models is, without doubt whatsoever, the key point for the industry.

The main limitation on wind modeling is the computational resource. For this reason, since the late 1990s the most extended approach is the use of mesoscale models for simulating the mean flow, which are then coupled offline with linear wind flow models early, and, more recently, with computational fluid dynamics (CFD) systems, for evaluating the high resolution effects linked to turbulent motions. This set of approaches have been demonstrated as powerful tools for modeling the flow dynamics but they fail when the atmospheric physical processes have an important role (e.g. katabatic winds or sea breezes).

Approach

The continuous improvement of the computational resource is opening the door for a new generation of mesoscale models coupled online with large-eddy simulation (LES) algorithms. LES divides the turbulent flow in such a way that eddies larger than the grid size are explicitly solved as a solution of the Navier-Stokes equations while smaller eddies need to be parameterized. Ideally, under this frame, the important physical processes occurring in the atmosphere (e.g. clouds, radiation or surface processes) interact with the turbulent flow, solving the main limitation of the other methods.

Main body of abstract

Due to the high computational specifications, LES has been reserved for idealized cases in the academic research for understanding the turbulent motions as well as for tuning the planetary boundary layer (PBL) parameterizations available in mesoscale models.

As more powerful computers have appeared, mesoscale models have increased the grid resolution from hundred to few kilometers, improving the representation of the dynamics and physical processes affecting wind farms. Today, computers are ready to reach grid sizes below hundred meters and with this, we have new challenges: can LES produce realistic turbulence patterns? Are mesoscale model approximations in radiation, clouds, etc valid for simulating the microscale or we need a new generation of physical packages? Is LES a suitable and promising tool for evaluating the wind resource or it is just a chimera?

In order to answer these questions, a set of modeling experiments using latest advance in Weather Research and Forecasting model, WRF-LES has been conducted for a full year period, for 4 sites with characteristics. The motivation for these experiments were: i) to understand WRF physical and dynamical response at very high resolution to a wide scenario of atmospheric conditions; ii) to evaluate the increase in accuracy of mean flow characterization with a turbulence enable model; iii) investigate the transition between kilometers to meters grid scales and the generation of real turbulence patterns; and finally, iv) to assess the operational feasibility for industry applications.

Conclusion

WRF-LES nested one year simulations results showed a robust dynamic modeling response to complex simulation and overall accuracy improvement respect typical PBL schemes. The improvement can be identified by the turbulence intensity, wind shear and veer bias reduction and better representation of real daily cycle profiles (including ramps). On the other hand, it has been found unrealistic turbulence generation that needs to be addressed carefully. More analysis are required to a better understanding of WRF adequacy to real conditions at under 100 m resolution.


Learning objectives
- Understanding LES. Differences between LES and current mesoscale models.
- Experiments in real scenarios with different topographic and climate features.
- Results: analysis of the WRF-LES outcomes for 1-year period including turbulence intensity, wind profile and energy cascade among others.
- Finally, we will shed light to the question: "Can mesoscale models reach the microscale?"