草地近地表风速脉动及其与平均风速、摩阻风速的关系

Characteristics of Wind Velocity Pulsation and Its Relation to Average Wind Velocity and Friction Wind Velocity

[目的]研究草地近地表脉动风速与平均风速、摩阻风速之间的关系,揭示草地风速脉动规律。[方法]利用三维超声风速仪对天然草地近地表风速进行连续观测。[结果]草地近地表风速存在明显的脉动特性,脉动强度与平均风速之间呈显著线性正相关。湍流度在较小风速下分布非常分散,随平均风速的增大而趋于集中,在2~14 m/s风速范围内概率分布峰值对应的湍流度为0.23。摩阻风速与瞬时风速之间缺乏相关性;1 s时距下摩阻风速与平均风速呈显著线性正相关,但风速脉动导致摩阻风速计算结果波动仍非常明显;1 min时距下摩阻风速波动范围降低至10%以下,摩阻风速与平均风速线性相关性极为显著。[结论]风速脉动对摩阻风速的计算有很大影响,采用1 s或1 min时距的平均风速,可有效降低这一影响。

[Objective]The characteristics of wind velocity pulsation and its relation to the average wind velocity and friction wind velocity were studied to reveal the rule of the wind velocity pulsation above grassland.[Methods]A sonic anemometer was used to observe the near surface wind velocity above the grassland.[Results]The near surface wind velocity had obvious pulsating characteristics,and there was a significant positive linear correlation between the pulsation intensity and the average wind velocity.The turbulence distribution was very scattered at a low wind velocity but tended to concentrate with the increase of the average wind velocity.The turbulence intensity at the peak of its probability distribution curve was 0.23 under a wind velocity ranging from 2 to 14 m/s.There was no correlation between the friction wind velocity and the instantaneous wind velocity.The friction wind velocity was positively and linearly correlated with the average wind speed at 1 s time intervals,but the fluctuation of the calculated results was still obvious because of wind velocity pulsation.At 1 min time intervals,the influence of wind pulsation on friction velocity was approximately 10%,and the linear correlation between friction wind velocity and average wind speed was extremely significant.[Conclusion]The wind velocity pulsation has a great influence on the calculation of the friction wind velocity.Using the average wind velocity at 1 s or 1 min time intervals can effectively reduce this influence.