Flow-plant interactions at a leaf scale: effects of leaf shape, serration, roughness and flexural rigidity |
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Authors: | Ismail Albayrak Vladimir Nikora Oliver Miler Matthew O’Hare |
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Institution: | (1) School of Engineering, Fraser Noble Building, University of Aberdeen, Aberdeen, AB24 3UE, UK;(2) Abt. Limnologie von Flussseen, Leibniz-Institut f?r Gew?sser?kologie und Binnenfischerei, M?ggelseedamm 301, 12587 Berlin, Deutschland;(3) Centre for Ecology and Hydrology Edinburgh, Bush Estate, Penicuik, Midlothian, EH26 0QB, UK |
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Abstract: | 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 × 103. 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. |
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