基于CFD降尺度的复杂地形风场数值模拟研究

Numerical Simulation of Wind Field in Complex Terrain based on CFD Downscaling

在计算机流体力学(Computational Fluid Dynamics,CFD)模式Fluent的基础之上修改传统的RANS湍流参数化方案,选用大涡模拟(Large Eddy Simulation,LES)的湍流方案,并引入温度层结的浮力模型,得到修改后的Fluent模式。使用中尺度预报模式WRF和WRF耦合修改前后的Fluent模式模拟江西鄱阳湖地区内吉山测风站处2010年12月至2011年3月4个月的风速、风向和2011年3月6日吉山站附近地形流场以及气温场的变化过程。结合观测资料的对比发现,WRF模式在耦合Fluent后,对吉山单站点风速风向的模拟效果得到改善。WRF耦合Fluent的模拟方法在Fluent修改后(算例2),相比修改前(算例1)可以更精确地模拟吉山站各高度处的风速风向。4个月70 m高度平均风速WRF、算例1和算例2的平均误差分别为3. 963,2. 727和2. 224 m·s^-1。算例2与观测的70 m高度风向玫瑰图匹配程度总体上比算例1更高。算例2还可以模拟出白天不稳定状态下的热浮力效应和空间分布不均匀且较大的湍动能,能模拟出夜间大气边界层的逆温现象,而算例1则不能。以上结果均表明在对Fluent模式修改后,WRF耦合Fluent的模拟方法对吉山站附近风场的模拟效果得到改善。

The traditional RANS turbulence parameterization scheme is modified on the basis of the Computational Fluid Dynamics model(Fluent),and the large eddy model(LES) turbulence scheme is selected,then the buoyancy model of temperature stratification is introduced,finally the modified Fluent model is obtained.The Weather Research and Forecasting model(WRF) and WRF coupled Fluent before and after modified are used to simulate the wind speed and direction of the 4 months from December 2010 to March 2011 in Jishan wind station in Poyang Lake region,Jiangxi and the evolution of the flow field and the temperature field near Jishan station in March 6,2011.According to the comparison of the observation data,it is found that:After coupling Fluent,the better WRF simulation result of the wind speed and wind direction in Jishan station is obtained.Compared with coupling original Fluent(Example 1),WRF coupling modified Fluent(Example 2) can provide more accurate simulation result of the wind speed and wind direction at each height in Jishan station.The average error of WRF,Example 1 and Example 2 for the 4 months 70 m height average wind speed are 3.963,2.727 and 2.224 m·s^-1 respectively.The Matching ratio to the observed wind direction rose of Example 2 is higher than Example 1 at 70 m height mostly.Example 2 not only can simulate the thermal buoyancy effect under the daytime unstable state and the spatial inhomogeneous and higher turbulent kinetic energy,but also can simulate the temperature inversion of the atmospheric boundary layer at night,while Example 1 can not.All the above results indicate that after the modification of Fluent model,the simulation result of the method that WRF coupled Fluent to the wind field near Jishan Station is improved.To sum up,this research provides a new method and basis for the prediction of the atmospheric flow field in the bottom of atmospheric boundary layer and the multiscale coupling simulation,and has also laid the foundation for the development and improvement of Fluent model in the future.