Drop impact onto pine needle fibers with non-circular cross section
Drop impact onto pine needle fibers with non-circular cross section
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DOI：
10.1063/5.0019310
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发表时间：
2020-09
影响因子：
4.6
通讯作者：
Amy P. Lebanoff;Andrew K. Dickerson
中科院分区：
文献类型：
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作者：
Amy P. Lebanoff;Andrew K. Dickerson
几千年来，松针随着降雨而进化。针对于雨滴的撞击具有很强的抵抗力，并且撞击雨滴的部分会留下来。松针还提供了独特的纤维轮廓，可用于研究细长结构上的液滴碰撞。在这项实验研究中，我们使用高速摄像来拍摄水滴对绿色、刚性支撑的沼泽松针的冲击，这些针叶具有非圆形横截面。撞击会导致水滴分裂成薄薄的、短暂的裂片，这些裂片会在几毫秒内崩溃，从而分裂出母滴。我们测量方向相关的波瓣形状和分离角、冲击力、纤维上的液滴扩散以及质量保留。针的圆形侧面撞击形成的裂片呈抛物线形，而楔形侧面的裂片则呈不规则形状。对于固定的液滴尺寸，圆形表面上的冲击力始终小于楔形表面所经历的冲击力，并且两个方向之间的冲击力的差异随着韦伯数的增加而增大。测试中的两个液滴尺寸中较小的一个在产生单位液滴重量的冲击力方面比较大的液滴更有效。冲击后，两个方向的纤维都保留了冲击跌落的残余质量。楔形表面在分裂液滴和脱落液滴残余物方面更有效。
Pine needles have evolved alongside rainfall for millennia. Needles are robust to raindrop impacts and the portions of mass impacting raindrops leave behind. Pine needles also provide a unique fiber profile by which to study liquid drop collisions on slender structures. In this experimental study, we use high-speed videography to film the impact of water drops onto green, rigidly supported Pinus palustris needles, which are of non-circular cross section. Impacts result in drop division into thin, ephemeral lobes, which collapse within milliseconds, splitting the parent drop. We measure orientation-dependent lobe shapes and separation angles, impact force, drop spreading on fibers, and mass retention. Lobes formed by impact with the rounded side of needles are parabolic in shape, while those with the wedged side are irregular. For a fixed drop size, impact forces on rounded surfaces are consistently less than those experienced by wedged surfaces, and the disparity in the impact force between the two orientations grows with the Weber number. The smaller of the two drop sizes on test is more effective at generating impact forces per drop weight than the larger drops. Post-impact, fibers in both orientations retain residual mass from the impacting drop. The wedged surface is more effective at splitting drops and shedding drop remnants.