跃移雪颗粒运动特性的数值模拟研究

Numerical simulation on the movement characteristics of saltating snow particles

摘要:

本文运用拉格朗日方法，根据雪颗粒的运动机理，对单个跃移颗粒运行轨迹进行了数值计算。同时，结合颗粒的受力特征，对影响其运动的一些参数，如粒子直径、摩擦速度和颗粒密度等进行了分析。结果表明，随着雪颗粒直径和雪粒密度的增大，粒子竖向受力与重力之比减小，粒子的跃移高度则随之增大；而当粒子起跳速度的不同时，水平方向受力的变化规律也表现不同，进而影响其水平方向的跃移长度。基于经验公式，建立了雪面侵蚀质量通量与跃移粒子数目之间的关系，计算了雪颗粒质量传输率，并与经典文献的计算方法进行了比较。结果显示，随着雪颗粒直径和摩擦速度的增大，粒子质量传输率随之增大；随着阀值摩擦速度增大，粒子质量传输率随之减小。本文的计算结果与Iversen经验公式吻合较好。

Abstract:

According to the movement mechanism of snow particles, the numerical simulation for a single saltating particle’s trajectory is carried out by using the Lagrange method. At the same time, some of parameters that affect the movement, such as particle diameter, the friction velocity and particle density are analyzed, based on the characteristics of forces applying to the particle. The results show that as the snow particle diameter or particle density increases, the ratio of particle vertical force to gravity decreases and the particle’s saltation height increases. The ratio of horizontal force to gravity varies with the particle’s liftoff velocity, thereby affecting its horizontal saltation length. Based on empirical formula, the relationship between the mass flux of snow surface erosion and the number of saltation particles is established to calculate the mass transport rate of snow particle. And the comparison is made with the calculated results from the classically empirical formula. It is shown that, with the growth of snow particle diameter and friction velocity, particle mass transport rate increases; particle mass transport rate decreases with the increase of the threshold friction speed. The present results in this paper coincide well with Iversen’s empirical formula.