Wickramarathna Lalith N, Noss Christian, Lorke Andreas
Institute for Environmental Sciences, University of Koblenz-Landau, Koblenz-Landau, Germany.
PLoS One. 2014 Mar 26;9(3):e92383. doi: 10.1371/journal.pone.0092383. eCollection 2014.
This study focuses on quantifying hydrodynamic trails produced by freely swimming zooplankton. We combined volumetric tracking of swimming trajectories with planar observations of the flow field induced by Daphnia of different size and swimming in different patterns. Spatial extension of the planar flow field along the trajectories was used to interrogate the dimensions (length and volume) and energetics (dissipation rate of kinetic energy and total dissipated power) of the trails. Our findings demonstrate that neither swimming pattern nor size of the organisms affect the trail width or the dissipation rate. However, we found that the trail volume increases with increasing organism size and swimming velocity, more precisely the trail volume is proportional to the third power of Reynolds number. This increase furthermore results in significantly enhanced total dissipated power at higher Reynolds number. The biggest trail volume observed corresponds to about 500 times the body volume of the largest daphnids. Trail-averaged viscous dissipation rate of the swimming daphnids vary in the range of 1.8 x 10(-6) W/kg to 3.4 x 10(-6) W/kg and the observed magnitudes of total dissipated power between 1.3 x 10(-9) W and 1 x 10(-8) W, respectively. Among other zooplankton species, daphnids display the highest total dissipated power in their trails. These findings are discussed in the context of fluid mixing and transport by organisms swimming at intermediate Reynolds numbers.
本研究聚焦于对自由游动的浮游动物产生的水动力尾迹进行量化。我们将游泳轨迹的体积跟踪与对不同大小且以不同模式游动的水蚤所诱导的流场进行的平面观测相结合。利用平面流场沿轨迹的空间扩展来探究尾迹的尺寸（长度和体积）以及能量学特征（动能耗散率和总耗散功率）。我们的研究结果表明，生物体的游动模式和大小均不会影响尾迹宽度或耗散率。然而，我们发现尾迹体积会随着生物体大小和游动速度的增加而增大，更确切地说，尾迹体积与雷诺数的三次方成正比。这种增加进而导致在较高雷诺数时总耗散功率显著增强。观测到的最大尾迹体积约为最大水蚤体体积的500倍。游动水蚤的尾迹平均粘性耗散率在1.8×10⁻⁶瓦/千克至3.4×10⁻⁶瓦/千克的范围内，观测到的总耗散功率大小分别在1.3×10⁻⁹瓦至1×10⁻⁸瓦之间。在其他浮游动物物种中，水蚤在其尾迹中表现出最高的总耗散功率。本文在中等雷诺数下生物体游动引起的流体混合和输运的背景下对这些发现进行了讨论。
