摘要
本文以平坦沙漠上定常、充分发展的风沙二相流为例分析了颗粒的跃移运动，在这种运动中颗粒吸收气流的机械能和水平动量向下输送，并在落地时传递给床面。本文还用拟流体观点分析了固相运动的特点：在床面上有较大的滑移速度，有较大的垂向速度脉动，但垂向的平均速度却为零，等等。并指出，这种速度脉动既不属于热运动，又不是湍流脉动，它是一种新形式的无规则运动，是颗粒跃移运动在连续介质模型中的反映，对风沙流的结构和流场中的细致平衡有很大影响。最后讨论了这种新型脉动产生的剪应力，给出了这种应力的近似本构式。这种应力有一个重要特征：非梯度型，即不能由当地的固相速度梯度完全决定。
In this paper, the saltation of sand grains was studied in the case of the steady and fully developed blown sands.It was found that moving sand grains always gain horizontal momentum and mechanical energy from the wind and transfer them down to the bed surface.The features of saltation was analysed in a continuum viewpoint:the particle phase has relatively fast slip velocity on the bed surface,and it has rather strong vertical velocity fluctuation while the average vertical velocity is exactly zero. The vertical velocity fluctuation of particle phase is neither(molecular)thermal motion nor turbulent fluctuation,so it is a new sort of fluctuation which is called PL fluctuation by the authors[6,7]. It was pointed out that this velocity fluctuation is the reflection of particle saltation in the continuum viewpoint, and it plays a rather important role in determining the structure of the blown sand field and maintaining the microscopical balance in this field.In the end,the shear stress corresponding to this fluctuation was discussed:the constitutive relation was given and an important character of this shear stress was discoverd that it is almost independent of the local velocity gradient of the particle phase.
出处
《地理学报》
CSSCI
CSCD
北大核心
1996年第5期434-444,共11页
Acta Geographica Sinica
基金
国家自然科学基金
关键词
风沙浪
跃移运动
风沙流结构
二相流
blown sands
saltation
velocity fluctuation
pseudo-fluid
continuum model,the structure of blown sand field
