Generation and characteristics of snowdrifts and powder snow avalanches

点击翻译按钮获取中文摘要

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