基于平板地形的流向均匀大气边界层比较分析

Comparative study on the uniform atmospheric boundary layer in flow direction based on flat terrain

为了得到适用于风电场计算的边界条件和参数设置,对平板地形进行计算分析。对常用的3种入流边界条件进行梳理和计算,确定了Z模型适合描述流向均匀的大气边界层,以此为基础对5组湍流模型参数进行了对比计算,选出了1组最佳参数。对不同首层网格高度、垂直网格数量和顶部边界条件进行了计算分析,结果表明:在不同首层网格高度的情况下,入口和出口的风速扩线几乎没有变化,湍动能扩线变化较小,耗散率扩线在4 m高度以下有偏差,且随着首层网格高度的增加,耗散率数值不断下降;计算域中若有地形,则顶部采用入口边界条件可避免空气从顶部流出,更加适合描述大气边界层。因此,为提高风电场模拟精度,宜采用式(6),(8),(9)组成的入口边界条件,配合第2组湍流模型参数进行计算,同时顶部应采用入口边界条件。

Numerical simulation of wind flow over flat terrain is carried out and analyzed to find out suitable boundary condition and model parameters setting method for wind farm calculation.Three commonly used inflow boundary conditions are comparied and the model Z is found most suitable for describing the flow-wise homogeneous atmospheric boundary layer flow. Based on model Z inflow boundary condition,five sets of turbulent model parameters are applied for further calculation and comparison, and a set of optimal parameters is selected. Calculations are performed with different first-layer cell height, number of vertical cells,and top boundary condition, theresults show that with different first-layer cell height the profiles of wind speed at the entrance and exit are almost the same, the profiles of turbulent kinetic energy have small changes, the deviation emerge between profiles of turbulence dissipation rate below 4 m height,and the value of the turbulence dissipation rate at exit decrease as the height of the first layer increase. If there are non-flat terrains in the calculation domain, the inlet boundary conditions at the top of the domain can avoid the outflow of air from the top, this condition is suitable for description of the atmospheric boundary layer flow. Therefore,in order to improve the simulation accuracy of wind farm flow field, the inlet boundary conditions composed by equations（6）,（8）, and（9）should be applied in conjunction with the parameters of the second set for turbulent models, and the inlet boundary conditions should be adopted at the top of the domain.