沙尘暴垂直输运的两相流理论Ⅱ：气柱挟卷模式

为了改进气块法对沙尘沉降问题的研究,文中利用气柱法,考虑沙尘气体与环境的交换作用以及气柱内湍流交换作用.计算结果表明,均匀场中有利于沉降的条件为较大的初始沙尘浓度扰动与较小的初始温度扰动,而且温度扩散系数越大越有利于沙尘沉降,沙尘浓度扩散系数越大越不利于沙尘沉降,湍流过程在均匀场中对沙尘沉降影响不大.考虑剑更真实的环境场,得出在环境的垂直沙尘浓度梯度与温度梯度的参数域中,初始沙尘扰动越大越有利于沙尘沉降,初始温度扰动越大,越小利于沙尘沉降.同时给出4种不利于沙尘沉降的过程:(1)上升浓度变化过程;(2)下沉浓度变化过程;(3)上升温度变化过程;(4)下沉温度变化过程.根据这些过程分析参数对沙尘沉降的影响得到:温度扩散系数越大越有利沙尘沉降;沙尘浓度扩散系数越大不利十沙尘沉降;垂直温度湍流交换系数越大有利于缓降区甚至是非沉降区的上升;垂直沙尘浓度湍流交换系数越大越有利于沙尘沉降.

The two-phase flow theory about dust storm's vertical transport,part Ⅱ:The air column entrainment model

To improve the air particle method in the previous paper, the air column entrainment method is used to study dust storm sedimentation. In the method, entrainment between the column and the environment is included, as is the turbulent exchange within the column. In a homogeneous environment, the computational results suggest that favorable conditions for sedimentation are larger initial dust concentration disturbances and smaller initial temperature disturbances; and furthermore, the larger the diffusion coefficient of temperature, the quicker the dust sedimentation, but the larger the diffusion coefficient of dust concentration, the slower the dust sedimentation. The turbulent process has little influence on the sedimentation. We further consider some more real environment conditions with vertical dust concentration and temperature gradients, the results suggest the same favorable conditions for the sedimentation in the above homogeneous environment. And meanwhile, four processes which are not conducive to the sedimentation are given: (1) ascending concentration variation process; (2) descending concentration variation process; (3) ascending temperature variation process; (4) descending temperature variation process. On the basis of the definitions of these processes, we can study the impacts of parameters on the sedimentation, and results show that the temperature diffusion is conducive to the sedimentation; and the dust concentration diffusion is not conducive to the sedimentation; the larger vertical temperature turbulent exchange coefficient is more conducive to ascending in the slowly sedimentation region, even in the non-sedimentation region; and the larger vertical dust concentration turbulent exchange coefficient is more conducive to the sedimentation.