Mean wind forces and peak pressure acting on wind turbine nacelles are investigated by the wind tunnel tests and empirical formulae for their coefficients are proposed. The mean drag coefficient in GL Guideline 2003 seems to be conservative than proposed values, however, peak pressure coefficients recommended in the guideline appears to be considerably underestimated compared with values obtained from the wind tunnel tests. The distributions of negative peak pressure coefficients on the wind turbine nacelles are similar to those on the corresponding building roofs, but values are larger than those in the current building codes, such as Eurocode, ASCE and AIJ.
The objective of this study is to investigate the differences in accuracies of wind predictions among four different meso scale meteorological models that will be used to develop a wind power prediction model. Hindcasts of winds are carried out using these models for four wind farms (three in Tohoku and one in Kanto districts). The performances of the models are discussed by comparing the simulated results with the wind data observed at these wind farms under different meteorological conditions. The results show that the meteorological models exhibit similar tendencies for general meteorological cases. On the other hand, significant differences are found in some cases such as those characterized by the passages of cold fronts, typhoons, and so on. The evaluations of the uncertainties in the meteorological model predictions show that the individual models have uncertainties of approximately 3 m/s in wind speed and 40° in wind direction. Additionally, the results also indicate that uncertainties attributable to the differences of the model design amount to only 10% of the total uncertainties, and that the initial and boundary conditions as well as the formulations of the models themselves can have more significant effects on the prediction accuracies.