Abstract
The wind turbulence intensity observed on a site have an influence the wind turbine energy production and the lifetime of the blades. It is therefore primordial to master this parameter for the optimization of the production. So therefore, this study is interested on the modelling of the wind turbulence intensity at 10 m above the ground on the coast of Benin. Four years of wind data measured on the site of Cotonou Port Authority (PAC) from 2011 to 2014 and recorded with a temporal resolution of 10 min were used. From the transport equation of turbulent kinetic energy followed by a numerical simulation based on the Nelder-Mead algorithm developed under the Matlab software, we proposed five new models for estimating the wind turbulence intensity. The results of the different simulations reveal that four of proposed models and based on the roughness, the speed of friction and the length of Obukhov better fit the data, during the periods of January, April, June, July, August, September and December. The estimators of the Root Mean Square Error (RMSE) and the Mean Absolute Error (MAE) vary from (0.02; 0.01) in December to (0.09; 0.07) in August. As for the model which is a function of roughness and the wind shear coefficient (expressed only according to the wind speed), it gives better performance whatever the time of the year and the atmosphere stability conditions. The estimations errors are included between (0.02; 0.01) obtained in December and (0.08; 0.06) observed in March. A comparative study between the existing models in the literature and the best model proposed in this study showed that only this model gives the best adjustment with the data. It can therefore be used on the sites where turbulence is influenced by the roughness and the atmosphere stability. Finally, from this model a new wind turbine design class has been proposed for the site of Cotonou. It takes into account the actual levels of turbulence observed and thus allow to optimize the energy production.
Highlights
Wind turbulence intensity is an important parameter for the induced loads evaluation by the wind on the wind turbines components as well as for their design (Ren et al 2018; Dimitrov et al 2015)
The model 3, which is a function of roughness and wind speed, better reproduces the different sequences of wind turbulence intensity whatever the time of year
The hypothesis formulated in this study that the average profile of wind shear can be expressed like a function of the wind shear coefficient is verified
Summary
Wind turbulence intensity is an important parameter for the induced loads evaluation by the wind on the wind turbines components as well as for their design (Ren et al 2018; Dimitrov et al 2015). In the atmospheric boundary layer where wind turbines are generally installed, this phenomenon of turbulence is high (Finnigan 1994) Such complex environments (near-ground) induce a stochastic variation in wind speed and turbulence intensity difficult to estimate (Evans et al 2017). They cause the angle of attack fluctuations for the blade element (Kamada et al 2011) inducing the fatigue loading which reduces their lifetime (Peña et al 2015; Cheung et al 2016; Stival et al 2017; Carpman 2011; Marino et al 2017; Dimitrov et al 2017; Kim et al 2015). IEC 61400 standard of the International Electrotechnical Commission (IEC) standards, has been designed by the European and the American countries to provide the wind turbine designer the valuable
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