可侵蚀地表上方含尘大气运动的数值模型

NUMERICAL MODELLING OF DUSTY ATMOSPHERIC FLOWS OVER AN ERODIBLE SURFACE

在稀相气固两相流的双流体模型框架下,导出含尘大气运动的基本方程,其中的源项考虑相间双向耦合作用;通过对基本方程进行无量纲化,求得控制气相和弥散相动力学行为的相似准则,包括弗洛德数、罗斯贝数、颗粒雷诺数、颗粒惯性参数、颗粒剪切横移参数、颗粒旋转横移参数和沙尘质量载荷率等.作为一个模型问题,研究可侵蚀地表上方充分发展湍流大气边界层流动对土壤颗粒的气动卷扬作用,其中计及气动阻力、萨弗曼升力和重力等因素的影响.为了克服由于沙尘跃移运动轨迹交叉导致流动参数多值性所造成的困难,引进拉格朗日坐标下弥散相连续方程.对两种不同风速和4种不同粒径条件下的沙尘运动进行数值模拟,给出相应情况中沙尘运动特性和密度分布剖面并讨论风速和粒径等参数的影响,还细致分析了含尘大气边界层中沙尘与气流之间的能量传递过程.所得的方程、准则和方法可以为土壤风蚀和沙尘暴等自然灾害的预报提供理论基础.

In the framework of the two-fluid model of dilute dusty gases, the present paper gives the governing equations for dusty atmospheric flows, where the two-way coupling is taken into account in the source terms. The similarity criteria are derived for dynamical behaviors of the carrier- and dispersed-phase and they include seven parameters such as the Froude number, the dust mass loading and so on. As a model problem, the aerodynamic entrainment of the dust and sand particles in the fully developed turbulent atmospheric boundary layer over an erodible surface are studied and the aerodynamic drag as well as the Saffman lifting and gravity forces are considered. To overcome the difficulties associated with the non-uniqueness of the flow parameters due to the intersection of particle trajectories, the continuity equation of the dispersed phase is introduced in the Lagrangian coordinates. The motion characteristics and concentration distributions of the dispersed phase are simulated numerically at two different wind speeds and four different particle sizes and the effects of wind velocity and dust size are discussed in detail. These results are also relevant to the energy exchange process between the two phases in the atmospheric boundary layer. The equations, criteria and method may be useful in interpretation of some natural disaster phenomena such as wind erosion and sand-dust storm.