【摘要】 风沙研究者非常重视对输沙通量随高度变化特征的研究,并为寻找可靠的测量手段付出了不懈的努力。基于高速摄影技术获得的沙粒平均水平速度与沙粒数的垂直剖面,推导了较低风速下环境风洞内输沙通量的垂直剖面。结果表明:沙粒平均水平速度随高度呈幂函数增加,颗粒浓度随高度的算数平方根呈指数衰减。由颗粒平均水平速度剖面与浓度剖面的乘积可获得输沙通量剖面。所获得的输沙通量随高度变化曲线在距床面1~3mm处均有一个明显的拐点,拐点上方输沙通量随高度呈指数衰减。在床面与拐点之间输沙通量没有明显的变化趋势,这可能是由于气流中颗粒间的碰撞以及颗粒与床面碰撞的影响。平均跃移高度和相对衰减系数是描述输沙通量随高度变化的两个重要参数,两者有着很好的相关性,表明了随着风速增加和沙粒粒径减小跃移颗粒可以达到更大的高度,随着风速减小与粒径增大,输沙通量迅速衰减。更多还原

【Abstract】 Aeolian researchers have recognized the importance of measuring the height profile of aeolian saltating flux and devoted a lot of effort to reliable measurement.In this paper,the height profiles of aeolian saltation flux are reconstructed on the basis of the profiles of mean particle velocity and relative particle concentration obtained by high-speed photography,a nonintrusive technique,in a wind tunnel.The results suggest that the mean particle velocity increases with height.The height profile of mean particle velocity can be expressed by apower function.Particle concentration decays exponentially with the square root of height.Mass flux profiles are derived by multiplying the mean particle velocity and concentration profiles.The reconstructed mass flux profiles are characterized by two sections.Above the peak point whose height was range from1 mm to 3mm,mass flux decays exponentially with height.Between the near-surface and the peak point layers,mass flux have no obvious change trend due to the influences of mid-air inter-particle collisions and initial impact on the bed.Two significant parameters,average saltation height and relative decay factor,are proposed to characterize variation with height of aeolian saltating flux.They are well correlated and imply that saltating particles can reach higher levels as wind velocity increases and particle size decreases and that mass flux decays more rapidly as wind velocity decreases and particle size increases.更多还原