沙粒启动机制的理论分析

Theoretical Analysis on Startup Mechanism of Sand Particles

从理论上对沙粒的初始启动与垂直抬升作了理论分析。结果指出,沙粒脱离地面的位置顺序是沙平面上凸拐点处、斜面上外突较大的地方、极大值点、水平面、极小值点以及凹槽的拐点处;提出了沙丘的平化运动、缩移运动与持相运动;气动力起沙的条件是:小粒径沙粒、大风、涡度场(与水平风同符号)、不稳定(层结不稳定与切变不稳定)以及粘性流;冲击起沙的条件是:大粒径沙粒、小风、涡度场(宜与水平风反符号)、稳定大气以及湍流;最后提出了沙尘暴启动的交替循环机制。

The initial start and vertical transportation of sand particle were analyzed in this paper. The results indicate that the most advantageous position to start sand particle is the inflexion with maximum, the next is the more undulate incline, the third is the dot with maximum, the forth is plane, the fifth is the dot with minimum and the last is the inflexion with minimum. The smoothing movement, wincing movement and holding phase movement may be the three forms of the particles＇ movement. The conditions of wind-carring starting sand are smaller diameter, gale, eddy field（ uniform orientation with gale）, instability and viscous flow;the conditions of impact-starting sand are bigger diameter, lower-speed wind, eddy field（contrary to wind）, stability and turbulence flow. In the last, this paper brings forward a mechanism of alternate circle to explain the forming of sandstrorm.