AN ANALYSIS OF THE CHARACTERS OF BLOWN SANDS
风沙二相流运动特点的分析

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 authors6,7]. 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.