中国沙漠 ›› 1988, Vol. 8 ›› Issue (1): 18-29.

• 论文 • 上一篇    下一篇


贺大良, 高有广   

  1. 中国科学院兰州沙漠研究所
  • 出版日期:1988-03-20 发布日期:1988-03-20

The Study of Sand Saltation Movement With High Velocity Cinecamera

He Daliang, Gao Youguang   

  1. Institute of Desert Research, Academia Sinica
  • Online:1988-03-20 Published:1988-03-20

摘要: 在沙漠所沙风洞中用HS-16型高速电影摄影机以500幅/S片速对平均粒径为0.2mm的石英沙进行了拍摄。共摄得57颗沙粒跃移运动的部份轨迹。计算了各沙粒的速度和加速度水平、垂直分量表明: 1.沙粒运动中存在着巨大的脉动, 最大加速度脉动值可达重力加速度的30倍, 这说明湍流脉动的粘性力在跃移运动中起着重要作用。2。加速度脉动具有各向同性, 其平均值并不大; 加速度水平分量的平均值在各运动阶段中始终为正值, 说明不断受到风力的拖曳; 加速度垂直分量始终为负值, 说明除重力作用外, 再无其它稳定持久的非接触力作用于跃移的沙粒上; 因此跃移沙粒起跳的原因必然是在离开地面之前受到三种接触力之中的一种作用, 三者必居其一。考虑到沙粒在飞行过程中带有高速旋转, 因而排除了振功起跳和冲击起动的可能。沙粒起跳最大可能的原因是斜面飞升力。

Abstract: We took the photos of the movement parameter of saltation quartz sands whose average diameter is 0.200 mm with HS-16 high velociy cinecamera in wind Tunnel, Institue of Desert Research, Academia Sinica. In total, the movements of 57 sand particles were partly observed under the standard velocity of 500 photos per second. We divide the locus into three parts, i.e. taking off(19 examples), level flying(30 examples) and falling down(8 examples), we also calculate the velocity and acceleration in both horizontal and vertical directions. Based on the photos and calculation, we come to the following conclusions: 1. During the three stages of gand movement, the vertical acceleration and the horizontal acceleration fluctuates a lot, the absolute fluctuation may be 30 times as big as acceleration of gravity, the fluctuation in vertical direction has nothing to do with that in horizontal direction. Thus, the viscous force which caused turbulent fluctuaion may play a great important role in sand saltation movement. 2. The big fluctuation in isotropous is flying plane, its average value is not very big, the vertical acceleration is negative. We deduced that there is no constant buoyance after leave the ground surface, viscous force is not the force which makes the sands take off. The force which makes the sands take off must be one type of the inertial forces, the impact from other particles Or the bounce of impacting particles, bevel flying and vibration. Because the sands revolve with high velocity after they take off, it is reasonable to give up the ideas that sands take off by impact or vibration. In our opinion, saltaion sanbs take off mostly through bevel flying. 3. During the three periods of saltation, the acceleration in horizontal direction is always positive, and that in vertical direction is always negative. Detailed information is as follows: ax ay Taking off(the average of 19 particles) 33.0m/s2 -15.3m/s2 level flying(the average Of 30 particles) 27.5m/s2 -13.8m/s2 Falling down(the average of 8 particles) 12.8m/s2 -10.6m/s2 From the table, we deduce that: 1) Sands were dragged downward by wind drawing force, the stressness of the dragging force is related to the relative disparity in velocities between sands and air flow, the disparity decreases during the sand movement from the taking off to the falling down. 2) The gravity is in action during the whole period of the movement, the acceleration in vertical direction is composed of two parts, i.e. the acceleration of gravity and the resistance in vertical direction. During the period of the taking off, the acceleration is big because it is caused by gravity and downward resistanc;During the period of level flying, vertical acceleration is a little Smaller; During the period of falling down, the vertical acceleration should de smaller than 9.8m/s2 because of the action of both gravity and upward resistance, although the figure is -10.6m/s2 in the paper, it's still allowed according to the range of calculation error.