沙尘重粒子在对流边界层中的扩散模拟

Numerical Simulation of Heavy Dust-Particulate Dispersion in Convective Boundary Layers

用拉格朗日随机模式 (LagrangianStochasticModel)结合大涡模拟所得对流边界层三维湍流场的时间序列 ,研究沙尘类重粒子在大气中的扩散特性。对地转驱动风速为 0、2、4m·s-1的对流边界层情况和重粒子落速为 0 2、0 4、0 6m·s-1的情况 (对应沙尘粒子直径约 5 3、80和 10 4 μm)分别进行模拟 ,并与被动粒子扩散的情况进行比较。模拟的被动扩散情况与水槽实验及前人的数值研究结果相符甚好。对重粒子扩散的模拟结果显示了 2方面的内容。一方面 ,较小的颗粒 (5 3μm)在边界层中的扩散特征与被动扩散接近 ,较大的颗粒 (10 4 μm)则不易扩散到边界层上层 ,这与经验直观的情况相符。另一方面 ,若保持其他条件相同 ,较强的平均风有利于较重的粒子在边界层中的沉降 ,这一结果有待观测验证。

Dispersion of heavy dust-particulate was simulated by means of a Lagrangian stochastic model with turbulence fields of convective boundary layers (CBL) derived from a large-eddy simulation model. Three geostrophic winds of 0.0, 2.0 and 4.0?m·s -1 were used for the CBL simulations. And three gravity falling velocities of 0.2, 0.4 and 0.6 (which corresponded to mineral dust diameters of 53, 80 and 104?μm, respectively) were employed to represent gravity effect of dust particulate. The model results were compared well with previous works of water tank experiments and numerical modelings for neutral particle diffusion. Diffusion of small particle (53?μm) behaved in CBL similar to the neutral one, while the large particle (104?μm) could hardly be carried to upper part of the CBL. An interesting result was that strong wind in CBL seemed to benefit heavy particle falling to the surface, if other atmospheric conditions kept the same. This phenomenon need to be verified by observation.