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Delegates are invited to meet and discuss with the poster presenters in this topic directly after the session 'The model chain: First steps towards tomorrow's technology' taking place on Thursday, 13 March 2014 at 09:00-10:30. The meet-the-authors will take place in the poster area.

Bastien Adamo ALSTOM Wind, Spain
Co-authors:

(1) ALSTOM Wind, Barcelona, Spain (2) Vortex, Barcelona, Spain

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Abstract

Benefits of multiscale modelling to reduce long term wind resource uncertainty: the Gouda case

Introduction

Wind flow modelling technology is improved year to year by the gained experience from the operational use of mesoscale modelling to screen wind resources and to synthesise long-term reference data. Using a virtual long term reference mast is a key advantage providing site specific long term data representing local wind regimes. However, when very complex wind flow is encountered current mesoscale models may be unable to fully reproduce its characteristics.
This work investigates a particular example of wind regime that shows a pronounced diurnal pattern, suggesting a complex interaction between flow scales.

Approach

A modelling experiment was conducted over the site to better understand the own flow circulations and the different mechanisms that feed the wind regime: large scale driven and modulated and triggered by the surrounding orography.
A set of WRF mesoscale model runs were designed to analyse the response and the sensibility of the model to different scales related parameters like domain extensions, grid-cell sizes and feedback between scales (nesting).
Accuracy of experiment runs was analysed to discriminate impact of the modelling at each chain stages. Finally, the benefits obtained were assessed through energy yield estimation.

Main body of abstract

The experiment is localised over the Gouda site, located in the South-African Western Cap region. The regional wind regime is characterized by a SE-NW wind rose parallel to the coast. The local wind regime has an unexpected strong East component representing nearly 80% of the overall energy.
The site is monitored with four meteorological masts with top anemometers at eighty meters height with registered data for one to three years.
The weather and wind regime can be described as a conjunction of large scale circulation from East, enhanced by low level jet phenomena, shaded by gravity/mountains waves and affected by thermal flows. Diurnal patterns and gravity waves shading are recognised from the observed time series.
Motivated by the unavailability of consistent long term reference data, a modelling task force has been designed in collaboration between Alstom and Vortex.
Sensibility of model to different flow downscaling configuration were analysed to investigate model transition between different scales. Domain shape, vertical and horizontal effective grid-cell sizes were varied through the experiment.
Post-processing and statistical analysis of the results led to select the optimal set of parameters to model Gouda wind flow.

Conclusion

Multiscale modelling has been found to be the key factor allowing characterization of complex flow such as the one occurring at Gouda site. Model adaptation and optimization based on site measurement verification did enable reducing uncertainty on the long term wind estimation and characterization of extreme events.
Among the benefits from manufactured point of view are the increased level of confidence in the selection of optimal wind turbine model and improved robust estimation of the expected energy yield.



Learning objectives
- Understand meso-scale modelling chain through different scales
- Visualize WRF meso-scale model responses on the meso/micro intermediate zone
- Show a real-case wind resource modelling example on complex flow regime
- Reduce wind assessment uncertainty thanks to an improved mesoscale model