Flow-plant interactions at a leaf scale: effects of leaf shape, serration, roughness and flexural rigidity
Flow-plant interactions at a leaf scale: effects of leaf shape, serration, roughness and flexural rigidity
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DOI：
10.1007/s00027-011-0220-9
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发表时间：
2012-04-01
期刊：
影响因子：
2.4
通讯作者：
O'Hare, Matthew
中科院分区：
文献类型：
--
作者：
Albayrak, Ismail;Nikora, Vladimir;O'Hare, Matthew
在7片叶片雷诺数为5~35×10(3)的明渠水槽中，试验研究了叶片形状、锯齿、粗糙度和弯曲刚度对流水阻力的影响及其随时间的变化规律。研究涉及相同表面积但具有三种形状(椭圆形、长方形和羽状)的人造叶片，三种弯曲刚性，光滑边缘和锯齿状锯齿，以及三种表面粗糙度组合(双面粗糙、单面粗糙/单面光滑和双面光滑)。形状是决定流-叶相互作用的最重要因素，弯曲刚度、锯齿和表面粗糙度影响阻力控制的大小，而不是方向。光滑边缘的椭圆形叶片受到的阻力较小，具有较好的流体动力形状，而矩形叶片的效率略低。羽状叶由于其复杂的几何形状，比其他叶片具有更大的阻力。羽状叶的12片小叶的流动分离可能阻止了叶片的重组，如小叶折叠和/或流线型。弯曲刚性强烈影响叶片的重组，增强锯齿效应，因为刚性很强的叶片表现出强烈的锯齿效应。此外，锯齿形通过增加湍流强度改变了叶片周围的湍流形态。在高雷诺数时，观察到表面粗糙度可以增强作用在叶片上的阻力。结果还表明，存在两种截然不同的流-叶相互作用模式：(1)当阻力统计完全由湍流统计控制时，在低湍流层的被动相互作用模式；(2)当叶片特性对阻力统计的影响与湍流贡献相当时，在高湍流水平上的主动相互作用模式。
The effects of leaf shape, serration, roughness and flexural rigidity on drag force imposed by flowing water and its time variability were experimentally studied in an open-channel flume at seven leaf Reynolds numbers ranging from 5 to 35 x 10(3). The study involved artificial leaves of the same surface area but with three shapes ('elliptic', 'rectangular' and 'pinnate'), three flexural rigidities, smooth-edge and sawtooth-like serration, and three combinations of surface roughness (two-side rough, one-side rough/one-side smooth, and two-side smooth). Shape was the most important factor determining flow-leaf interactions, with flexural rigidity, serration and surface roughness affecting the magnitude but not the direction of the effect on drag control. The smooth-edge elliptic leaf had a better hydrodynamic shape as it experienced less drag force, with the rectangular leaf showing slightly less efficiency. The pinnate leaf experienced higher drag force than the other leaves due to its complex geometry. It is likely that flow separation from 12 leaflets of the pinnate leaf prevented leaf reconfiguration such as leaflets folding and/or streamlining. Flexural rigidity strongly influenced the leaf reconfiguration and augmented the serration effect since very rigid leaves showed a strong effect of serration. Furthermore, serration changed the turbulence pattern around the leaves by increasing the turbulence intensity. Surface roughness was observed to enhance the drag force acting on the leaf at high Reynolds numbers. The results also suggest that there are two distinctly different flow-leaf interaction regimes: (I) regime of passive interaction at low turbulence levels when the drag statistics are completely controlled by the turbulence statistics, and (II) regime of active interaction at high turbulence levels when the effect of leaf properties on the drag statistics becomes comparable to the turbulence contribution.