The Transport of Sand by Wind
The Transport of Sand by Wind
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DOI：
10.2307/1786411
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发表时间：
1937-05
期刊：
影响因子：
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通讯作者：
R. Bagnold
中科院分区：
文献类型：
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作者：
R. Bagnold
当然，这个问题只是固体粒子在流体中输运这一普遍问题的一个特例。无论沙子是通过空气还是水运输，所涉及的雷诺数都是相同的数量级，而且颗粒的运动类型以及它们对流体产生的阻力似乎都是相同的，尽管由于沙子和流体的密度比在两种情况下差异很大，因此不应该画出太接近的平行线。但是，由于空气实验，特别是皮托管速度测量的比较简单，因此，从对沙-气输送的研究中有可能出现适用于沙-水输送的新事实。在空气中，沙子的行为和雪的行为似乎更相似。例如，G.塞利格曼在他的书《雪的结构和滑雪场》中描述的“风板”雪的特殊固体形成，似乎在某种类型的沙沉积中有非常精确的对应物，可以通过实验重现。在这里，我们可以从用沙子做的实验中学到很多关于雪的漂移，因为沙子是一种方便得多的介质。所处理的颗粒被定义为坚硬的颗粒，小到足以被流体的直接前进速度所驱动，但又太大，在飞行过程中不会受到流体内部运动的较弱速度的严重影响。这些内部运动严重影响了尘埃的小颗粒，但它们的行为超出了本文的范围。作为沙粒对风的易感性的一个例子，当以4米/秒的速度射入静止的空气时，通常在沙丘顶部发现的细粒（直径0-25毫米）（每小时9英里），在速度降低50%之前行进20厘米。在风的驱动下，沙粒在边界（或“跳跃”）中移动，急剧上升到气流中，并在那里被风的压力推动着前进。由于它们的重量，它们再次落到地面，但从空气中获得的水平速度成分很高。对…的影响
The subject of course is but a special case of the general problem of the transport of solid particles by fluids. The Reynolds' Numbers involved are of the same order, whether sand is transported by air or water, and the type of motion of the grains, and their resulting drag on the fluid, appear to be much the same, though too close a parallel should not be drawn since the density ratios of sand and fluid differ greatly in the two cases. But because of the greater simplicity of experiments with air, especially in pitot-tube velocity measurements, it is possible that new facts applicable to sand-water transportation may emerge from the study of sand-air transportation. There would appear to be a closer resemblance between the behaviour of sand in air and that of drifting snow. For instance the peculiarly solid formation of "wind-slab" snow which G. Seligman describes in his book, 'Snow Structure and Ski Fields,' seems to have a very exact counterpart in a certain type of sand deposit which can be reproduced experimentally. Here again much might be learnt about snow-drifting from experiments made with sand, which is a far more convenient medium. The particles dealt with are defined as hard grains small enough to be set in motion by the direct forward velocity of the fluid, but too massive to be seriously affected during their flight by the less violent velocities of the fluid's internal movements. Small particles of dust are seriously affected by these internal movements, but their behaviour is beyond the scope of this paper. As an example of the susceptibility of sand grains to wind motion, a fine grain of the size (0-25 mm. diam.) commonly found at the crests of dunes when shot into still air at a speed of 4 m./sec. (9 miles per hour), travels 20 cm. before its speed is reduced by 50 per cent. Wind-driven, the sand grains move in bounds (or in "saltation" 2), rising steeply into the air stream, and there being urged forward by the pressure of the wind upon them. By their weight they fall to the ground again, but with a high horizontal velocity component acquired from the air. On impact with