Characteristics of Near Surface Winds over Different Underlying Surfaces in China: Implications for Wind Power Development

Accurate wind and turbulence information are essential to wind energy research and utilization, among which wind shear and turbulence intensity/scale have seldom been investigated. In this paper, the observational data from the 100-m high wind towers in Xilinhot in Inner Mongolia (2009–10; grassland region), Huanghua in Hebei Province (2009–10; coastal flat region), and Xingzi County in Jiangxi Province (2010–11; mountain–lake region) are used to study the variations in near surface winds and turbulence characteristics related to the development of local wind energy over different underlying surfaces. The results indicate that (1) the percentage of the observed wind shear exponents exceeding 0.3 for the grassland region is 6%, while the percentage is 13% for the coastal flat region and 10% for the mountain–lake region. In other words, if the wind speed at 10 m is 10 m s^–1, the percentage of the wind speed at 100 m exceeding 20 m s^–1 for the grassland region is 6%, while the percentage is 13% for the coastal flat region and 10% for the mountain–lake region. (2) In terms of the turbulent intensity in the zonal, meridional, and vertical directions (I_u, I_v, and I_w, respectively), the frequencies of I_v/I_u < 0.8 in the grassland, coastal flat, and mountain–lake regions are 23%–29%, 32%–38%, and 30%–37%, respectively. Additionally, the frequencies of I_w/I_u < 0.5 in the grassland, coastal flat, and mountain–lake regions are 45%–75%, 52%–70%, and 43%–53%, respectively. The frequencies of I_v/I_u < 0.8 and I_w/I_u < 0.5 in each region mean that I_u is large and the air flow is unstable and fluctuating, which will damage the wind turbines. Therefore, these conditions do not meet the wind turbine design requirements, which must be considered separately. (3) At 50- and 70-m heights, the value of the turbulence scale parameter Λ in the grassland region is greater than that in the coastal flat region, and the latter is greater than that in the mountain–lake region. Therefore, under the same conditions, some parameters, e.g., the extreme directional change and extreme operating gust at the hub height in the grassland region, are greater than those in the coastal flat region, which are greater than those in the mountain–lake region. These results provide a reference for harnessing local wind energy resources and for the selection and design of wind turbines.