摘要:
沙尘暴和尘卷风等风沙运动的静电场是空气流场中沙粒间的碰撞摩擦带电及沙粒粒径的分层效应引起的,本文耦合沙粒摩擦荷电模型和风沙运动气固两相流模型,提出了离散单元法与计算流体动力学结合的数值方法.数值模拟计算表明电荷呈中性的沙粒临界直径为300μm;在充分发展的水平风沙流中,细小的沙粒带负电,较大直径的沙粒带正电,所模拟的沙粒带电的荷质比及水平风洞试验段的电场强度与实验测量值一致,验证了风沙运动的电场-流场耦合模型及数值计算方法的合理性.本文基于沙粒摩擦荷电机理的风沙运动气固两相流模型提供了理解风沙运动静电场产生的一种物理机理.
Abstract:
The electrification of wind-blown sand,such as dust storms and dust devils,is known as the tribo-electric effect of sand particles and the stratification of different size particles.Combined with the grain electrification model,a new numerical method of gas-solid two-phase flow is developed for the simulation of wind-blown-sand two-phase flow,which is a hybrid method of computational fluid dynamics and discrete element method（CFD-DEM）.In the developed wind-blown-sand two-phase flow of horizontal wind tunnel,the simulation results indicate that large size grains become positively charged while small size grains become negatively charged,and the critical diameter of grain with electric neutrality is about 300μm.The simulated charge-to-mass ratio and electric field intensity of the wind-blown sands in the field wind tunnel approach to the measured data,showing the rationality of this numerical method.The simulation also demonstrates that there occurs the maximum of electric field intensity over the sand bed of the field wind tunnel,which is the reason why the electric grounding of the field wind tunnel is used in experiment.The coupling of grain electrification model and gas-solid two-phase flow method provides an important tool for interpreting laboratory and field observations of wind-blown sands and insights into the physical dynamics of dust storms and dust devils as well.
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