Analysis of urban turbulence intensity observed by Beijing 325-m tower and comparison with the IEC turbulence model for small wind turbines

Abstract

The accurate assessment of turbulence intensity is crucial for the effective utilization of urban wind energy. However, the Normal Turbulence Model (NTM) prescribed by the IEC standard has not been adequately evaluated for its applicability in urban environments. To address this gap, we analyze one-year continuous turbulence observations collected at multiple levels on a 325-m meteorological tower in Beijing. The results show that: the turbulence intensity follows the Johnsonsb distribution instead of the Normal distribution in the IEC standard; it has significant diurnal variation and piecewise power-law vertical variation; the NTM underestimates turbulence intensity at most times and heights. A new turbulence intensity model with an exponential form is proposed, which significantly outperforms the NTM. Further, the exponential model fits the observations better than power-law model that outperforms the NTM. In terms of the fitting errors to the measurements, the full-year, monthly, and hourly RMSE (MAE) of this model are reduced on average by 51.81% (54.31%), 33.04% (34.38%) and 29.46% (28.24%) compared to that of the power-law model. These findings will contribute to the revision of the IEC standards governing the safe operation of small wind turbines in complex wind environments such as urban areas.