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Generation and characteristics of snowdrifts and powder snow avalanches

雪堆和粉雪崩的产生及特征

基本信息

批准号：
13650565
负责人：
FUKUSHIMA Yusuke
金额：
$ 2.18万
依托单位：
Nagaoka University of Technology
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2001
资助国家：
日本
起止时间：
2001 至 2003
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-13650565/
关键词：
snowdrifts powder snow avalanches numerical simulation k-ε turbulence model non-conservative inclined thermal solid-gas two phase flow snow entrainment coefficient sediment suspension flow 煙型雪崩発生・流動機構加速・減速発生機構流動機構数値解析乱流モデ

项目摘要

The generation and characteristics of powder snow avalanches have been studied as the treatment of solid-gas two phase flow. The snowdrifts are closely related to the occurrences of powder snow avalanches in mountainous area. Snowdrifts themselves are generated by strong wind which suspends large amount of snow particles. When snowdrifts may occur on the slope, the gravity excess of mixture of snow particles and air can accelerate to become a powder snow avalanches.These mechanism of the generation of powder snow avalanches was simulated numerically using the k-ε turbulence model. In the simulation, the solid-gas two phase flow was replaced by the solid-liquid two phase flow and the gravity excess was expressed by the salinity concentration in water.The flow characteristics of the accelerated inclined thermals were discussed precisely by the results of the numerical simulation using the k-ε turbulence model. The drawings of concentration contours and velocity vectors have helped us to … More get the idea of the inner and outside structure of thermals. The variation of the travel speed, the height and the maximum concentration of a thermal in the flow direction were estimated from the numerical results of the simulation of thermals. Those mass characteristics of thermals are well agreed with the experimental results in the laboratory.The characteristics of the snowdrifts also were discussed by the numerical simulation using the k-ε turbulence model. The problem in the simulation was estimation of the boundary value of concentration of snow particles ; i.e. the snow entrainment coefficient. The values of the snow entrainment coefficient were derived from the numerical simulation and the actual values from the field observations and wind tunnel experiments of snowdrifts. The values of snow entrainment coefficient in air were smaller then those of the sand entrainment coefficient in water. The one reason was the large density difference of snow case in air comparing with the sand case in water. Thus, the snow particles are difficult to be suspended by the turbulent motion of air. On the contrary the sand particles can be easily suspended by the turbulent motion of water. The specific gravity of sand particles in water is the zero order, however, the specific gravity of snow particles in air becomes quite large values. The other reason was that diameters of snow particles were measured by the snow particle counter(SPG) in the optic principle. This method may over-estimate of diameter assuming that the shape of the particle is a sphere. Actually the shape of snow particles is not a sphere but having wide variety of crystals. Less

本文将粉雪雪崩作为气固两相流的处理，研究了粉雪雪崩的发生和特性。山区雪堆与粉雪雪崩的发生密切相关。雪堆本身是由强风悬浮大量的雪颗粒产生的。利用k-ε湍流模型对坡面上可能发生雪堆时，雪颗粒与空气混合物的重力过剩加速形成粉雪崩的机理进行了数值模拟。模拟中，将固气两相流替换为固液两相流，重力过剩用水中盐度表示，利用k-ε湍流模型的数值模拟结果，对加速倾斜热气流的流动特性进行了较为精确的讨论。浓度等值线图和速度矢量图帮助我们 ...更多信息了解热气流的内外结构。根据热气流的数值模拟结果，估算了热气流在流动方向上的传播速度、高度和最大浓度的变化。热气流的质量特性与实验结果吻合较好，并采用k-ε湍流模型对雪堆特性进行了数值模拟。模拟中的问题是雪颗粒浓度边界值的估计;即雪夹带系数。雪卷吸系数的计算值是由数值模拟和雪堆的野外观测及风洞试验得到的。空气中雪的挟沙系数小于水中的挟沙系数。其原因之一是空气中的雪壳密度与水中的沙壳密度相差较大。因此，雪颗粒很难被空气的湍流运动悬浮。相反，沙粒很容易被水的湍流运动所悬浮。沙粒在水中的比重为零级，而雪粒子在空气中的比重则变得相当大。另一个原因是雪粒子计数器（SPG）测量雪粒子直径的光学原理。假设颗粒的形状是球形，该方法可能高估直径。实际上，雪粒的形状不是球形，而是有各种各样的晶体。少