【作者】 张洁；

【导师】 黄宁；

【作者基本信息】 兰州大学 ， 固体力学， 2008， 硕士

【摘要】 根据床面雪粒粘连程度的不同,建立不同的起动模型,并讨论温度在-30°C-0℃的范围内,起动风速与粒径、温度以及积雪时间的关系。结果表明:当其他因素不变时,临界起动风速随着雪粒粒径的增大而增大;在一定积雪时间内,临界起动风速随时间增加而增加,最终达到一个稳定的值;在温度低于零度时,临界起动风速随雪表温度的增大而增加。建立单颗雪粒的运动模型,分别讨论了在不同情况下各种因素对雪粒运动轨迹的影响。结果表明:除重力和拖曳力外,saffman力、magnus力、静电力以及运动随机性对雪粒的运动也有重要的影响,并且随着风速、雪粒粒径、密度的变化各因素的影响程度也发生不同程度的变化。基于对雪粒起动、运动机理的分析,结合初速度分布函数,建立稳态的风雪流计算模型,并对稳定状态下的风雪流结构进行分析,将分析的结果与风洞试验的测量值进行了比较,结果显示:风雪流发展稳定后,运动雪粒对风场有较为明显的修正作用;稳定状况下雪粒的数浓度和水平质量通量均随高度呈负指数分布,并且在考虑saffman力、magnus力以及静电力以后计算结果更接近实测值。当运动随机性较大时,其对雪粒的数浓度和水平质量通量的计算结果会有明显影响。通过击溅函数模拟了风雪流的发展过程,讨论了不同风速下风雪流发展时间的变化,模拟所得的稳定状态下的输雪通量与实验结果吻合较好。更多还原

【Abstract】 According to the adhesion degree of snow grains on the bed, this paper have established different initiation models and respectively analyzed the relationship between threshold wind velocity and particle size, temperature and snow cover time at the temperature range of - 30℃- 0℃. The results show that when other factors do not change, the critical threshold wind velocity will increase with the particle size of snow grains, the critical threshold wind velocity increase with time of snow cover, and reach a steady value finally; when the temperature below zero, the critical threshold wind velocity will increase with the temperature of snow surface.Established a movement model of single snow particle and discussed the influence of various factors on motion trajectory of snow particle at different situations. The results show that besides the gravity and the drag force, the saffman force, the magnus force, the electric field force as well as motion randomicity also have important influence to a snow grain movement, which changes with different wind speed, particle size and particle density.Based on the analysis of threshold and movement mechanism of a snow particle, a computation model of the evolution process of wind-snow drift has been established, combined with initial velocity distribution function we analyze the structure of the snow drift and compare it with the value of cold wind tunnel test. The result demonstrated that after the wind blow snow develops to a stable state, the movement of snow grains has the obviously effects on the wind field; snow grain number’s density and the horizontal quality flux obey the negative exponent distribution with height, and the computed results will be closer to the actual when the effects of Saffman force Magnus force and electric field force are taken into consideration. Furthermore the motion randomicity of mobile particle has obvious effects on the computed results too. On the basis of splash function, we simulated the evolution of snow drift and calculated the time for the entire system to reach a steady state of snow drift at several wind speeds. Compared to the experimental results of snow flux in steady state, it suggests that the simulating results are good accordance with the experimental results.更多还原