复杂地形风场的大涡模拟研究

The simulation method of wind field in complex terrain is the way to assess the wind energy resource, and the accurate simulation of wind field in complex terrain is the prerequisite for reasonable development and grid scheduling. The project intends to get a way to simulate the wind field in complex terrain as a real case based on large-eddy simulation method in WRF model with multiple nests from synoptic scale to turbulent scale and analyze the 3D characteristics of wind field and turbulent field in complex terrain. The LES parameter such as Cs, Ck, Ce and Cb will be calculated or fitted by the turbulent-gradient data of many masts in Poyanghu complex terrain area for a whole year that was already collected. The parameter of existing LES model of WRF model will be modified by the calculated value such as linear Smagorinsky model and nonlinear backscatter and anisotropy (NBA) model, and the dynamic Smagorinsky model based on Lagrangian-averaged scale-dependent (LASD), dynamic reconstruction model (DRM) and wall-in-law method will be introduced into WRF model. Multiple nests of finest horizontal resolution as 200m, 100m or 50m will be simulated with four LES methods in real cases in Poyanghu complex terrain. LES method is adopted in all model domains that are simulated with horizontal resolution less than 1km. The real case in complex terrain simulated with WRF-LES method is achieved by that multical nests of LES method are driving by simulation result with TKE method in coarser resolution in real time. The simulated turbulent stress will be validated with the observational data that is calculated by turbulence data, and then the conclusion would be drawn as which LES model and wall-in-law with which horizontal resolution is suitable for simulation of wind and turbulence field in complex terrain. And finally, the optimal LES simulation method and best setting of horizontal resolution is achieved. And then the 3D characteristics of wind and turbulent field in complex terrain will be achieved by analysis the simulation results in typical weather condition in different seasons. And then the sensitivity tests are simulated by changing the area of Poyanghu Lake to study the effect of variation of lake area on meteorological environment, wind filed and turbulent field in the extreme wet period and extreme dry period.

复杂地形下风场的模拟技术可以为我国风能资源的精细评估提供方法，风场的准确模拟也是风能资源合理利用的前提条件。本项目在WRF模式中建立基于大涡模拟技术复杂地形下实际算例从天气到湍流尺度的多重嵌套模拟计算，分析复杂地形风场和湍流场特征。基于复杂地形下湍流梯度观测修正WRF模式中LES方案SMAG和NBA模型参数，并引入基于LASD的动力SMAG模型和DRM模型及近地面耗散项，采用四种LES方案多重嵌套对鄱阳湖地区模拟，最高水平分辨率分别为200m、100m和50m，低于1km分辨率区域均采用LES方案，以WRF中TKE湍流方案较粗分辨率结果实时驱动多重嵌套的LES模拟来实现LES技术对实际算例的模拟计算。研究得出复杂地形下最优LES方案及最佳水平分辨率设置。分析鄱阳湖区典型天气条件下流场和湍流场特征，并通过改变湖区面积，研究极端丰水季和极端枯水季对该地区近地层流场和湍流场的影响。

本项目中实现了通过鄱阳湖地区测风塔湍流观测资料计算了大涡模拟方案参数，SMAG模型参数Cs 约为0.24~0.27，耗散系数Ce为0.22~0.38，扩散系数Ck为0.12~0.13，后向散射系数Cb为0.30；实现了WRF模式中复杂地形下从天气尺度到湍流尺度的多重嵌套大涡模拟计算，该方法的建立是基于大量复杂地形下实测湍流超声数据拟合的LES参数、基于LASD的动力SMAG模型和DRM模型的引入以及SMAG模型、NBA模型不同LES方案不同水平分辨率的模拟结果对比检验，对比发现NBA方案获取风速略微比SMAG方案风速偏低1m/s左右，而比LASD和DRM方案偏低约2m/s。从整体上来讲，所有方案获取的鄱阳湖区近地面10m和70m的风速数据均偏高于实测结果，但是NBA方案结果比其余方案更接近于实测结果，误差更小；实现了WRF模式针对鄱阳湖区进行多种水平分辨率的大涡模拟方案数值模拟研究，百米精细水平尺度的模拟结果可以很好的描述鄱阳湖区复杂地形地貌特征下的风场特征，模拟风速和风向与实测比较接近，模拟的风向和风速频率也与实测较为吻合，不同水平分辨率间校验指标间有一些略微的差异，但不明显；运用复杂地形下最优LES方案最佳水平分辨率设置的WRF模式研究鄱阳湖复杂地形地区典型天气条件下近地层流场分布特征、以及鄱阳湖区面积变化对该地区近地层气象环境的影响，丰水水面面积情况下风速明显增大，整个区域水面和陆地地区的气温降低，相对湿度增加，平均气压影响不大；枯水面积条件下使得鄱阳湖湖区及其附近风速下降，温度明显升高，相对湿度降低。