【作者】 任珊；

【导师】 黄宁；

【作者基本信息】 兰州大学 ， 工程力学， 2011， 博士

【摘要】 由于沙粒跃移过程的复杂性和随机性以及实验条件的限制,现有的模型很少计及沙粒空中碰撞对风沙流的影响,本论文针对此现状建立了同时考虑沙粒空中碰撞机制和风沙流自平衡机制的风沙跃移云模型,定量分析了沙粒空中碰撞机制对风沙流结构的影响。主要工作如下：1.在风场-沙粒相互耦合的风沙运动数值模型的基础上,结合已有空中碰撞概率模型建立了同时考虑沙粒空中碰撞机制和风沙流自平衡机制的风沙跃移云模型,模拟了考虑跃移沙粒空中发生碰撞时输沙率沿高程的分布,及沙粒空中碰撞机制对沙粒跃移轨迹的影响。2.基于上述的风沙跃移云模型,结合起跳沙粒合初速度分布函数,模拟了垂向初速度,沙粒起跳合初速度,以及同时考虑合初速度和沙粒空中碰撞机制时的输沙率和单宽输沙率。结果表明粒径大于0.5mm时,同时考虑合初速度和空中碰撞的单宽输沙率更接近实验值,而粒径较小(<0.5mm)时,模拟过程中应考虑沙粒形状的影响。3.结合上述风沙跃移云模型,分析比较了非球形沙粒和球形沙粒形成的风沙流中输沙率和单宽输沙率,发现沙粒形状对输沙率影响显著。相同条件下,不同形状沙粒产生的输沙率不同,甚至会相差几倍；对于同一形状的非球形沙粒,其纵横比越小输沙率越小；与球形沙粒相比,对于椭球和圆柱形的沙粒,当纵横比大于1时,其输沙率增大,而纵横比小于1时,其输沙率减小。因此沙粒形状也是一个较重要的影响因素。4.考虑了沙粒一地表碰撞、沙粒的空中碰撞及风场-沙粒间的相互耦合作用,建立了同时考虑现有风沙流自平衡机制和沙粒空中碰撞机制的风沙跃移运动发展过程数值模型,模拟了考虑沙粒空中碰撞机制时风沙跃移运动从起始阶段至风沙流达到平衡状态的发展过程及在发展过程中单宽输沙率以及沙粒空中碰撞整体概率随时间的变化。更多还原

【Abstract】 For the sand saltation is a stochastic and complex process, the exiting model rarely consider the effects of mid-air collision between sand particles on wind-sand flow. In this dissertation, a theoretical model is suggested to mathematically describe the wind-sand flow by considering the mid-air collision mechanism as well as the existing wind-particle feedback mechanism, and quantitatively simulate the influence of mid-air collision mechanism on structure of the wind-sand flow. The main works are concluded as follows:1. Based on the exiting mid-air collision probability model and the theoretical modeling of the wind blown sand movement at the steady state with concerning the coupled interaction between saltation particles and wind, a model is established with consideration of the mid-air collision mechanism and the wind-particle feedback mechanism to simulate the sand mass flux at heights and sand particle’ trajectory.2. On the base of the theoretical model above and the probability distribution function which considers both horizontal and vertical velocity, the mass flux against heights and sand transport rate against wind friction velocity are discussed under three conditions which are only considering the probability distribution function of vertical velocity, considering the probability distribution function of horizontal and vertical velocity, and both considering the probability distribution function of horizontal and vertical velocity and the mid-air collision mechanism. It suggests that the results, with consideration of the probability distribution function of horizontal and vertical velocity and the mid-air collision mechanism, are less and much closer to the corresponding values of experiments when the sand diameter is large than 0.5mm. While for the sand diameter less than 0.5mm, it might consider other factor, such as irregular shape of sand particle.3. Then the shape of sand particle is taken into account in the theoretical model. Choose six non-spherical sand particles to analysis the influence of different particle shape on the structure of wind-sand flow. The simulation results show that the shape of particles has great influence on the mass flux; at the same situation, the difference of mass flux of different shape particle may be up to several times; for same shape, the mass flux is increasing with the aspect ratio; for the elliptical particle and cylindrical particle,, when the aspect ratio is larger than one, their mass flux is larger then the spherical particle’s, while the aspect ratio is less than one, their mass flux is less then the spherical particle’s. So the shape of sand particles is also an important factor of mass flux.4. A theoretical model is developed to mathematically describe the evolution of wind-sand flow by considering both the exiting wind-sand feedback mechanism and the particle mid-air collision mechanism, based on the theoretical model of wind-sand flow evolution which only considers the interaction between wind and sand, the sand-bed collision. Then the entire process of sand saltation is simulated quantitatively. The simulated results show that the particle mid-air collision mechanism makes a great contribution to the whole evolution process and the sand transport.更多还原