Importance of Body Stance in Fog Droplet Collection by the Namib Desert Beetle
Importance of Body Stance in Fog Droplet Collection by the Namib Desert Beetle
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DOI：
10.3390/biomimetics4030059
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发表时间：
2019-09-01
期刊：
影响因子：
4.5
通讯作者：
Megaridis, Constantine M.
中科院分区：
文献类型：
--
作者：
Chakrabarti, Unmeelan;Paoli, Roberto;Megaridis, Constantine M.
Onymacris unguicularis是一种生活在纳米比亚沙漠沿海地区的甲虫物种，其雾晒行为最近引起了工程界的注意，因为它提出了一种可行的仿生方法来解决地球仪干旱地区的集水问题。以前的研究集中在观察和分析甲虫的鞘翅特性以及这些特性如何影响集雾率。在雾晒太阳时，Onymacris unguicularis的头部姿态是有据可查的。然而，这一立场如何影响液滴收集尚未研究到现在。本文从计算流体动力学的角度解决了这个问题，其中三维数值模拟被用来表征雾流特性周围的一个简化的几何形状模仿甲虫的身体。模拟采用双向耦合之间的气体流和分散的雾相考虑的反馈效应的雾液滴上的载体流体（空气），并假设液滴被捕获后，击中elytron表面。该研究考虑了自由流速度和液滴体积分数的几种组合。分析表明，有一个范围内的头部姿态角，对应于35度和45度之间的甲虫相对于地平线的倾斜，最大限度地收集水的甲虫的背部，在定性协议与观察在自然界和实验室实验。提出了一个理论基础来解释这种现象，发现特定的头部姿态对应于甲虫鞘翅表面上方流体颗粒的最大停留时间。这反过来又指定了水滴在甲虫上方发展的边界层中被捕获并随后击中它们被捕获的表面的最大可能性。结果揭示了甲虫的身体周围的流体流动模式的重要性，除了鞘翅的微物理特性时，水滴收集效率的可靠预测寻求。
The fog-basking behavior of the Onymacris unguicularis, a beetle species living in the coastal regions of the Namibian desert, has recently caught the attention of the engineering community, as suggesting a viable biomimetic approach to address the problem of harvesting water in arid regions of the globe. Previous research has focused on observation and analysis of the beetle's elytron properties and how these affect fog-collection rates. The head stance taken by the Onymacris unguicularis when fog basking is well documented. However, how this stance affects droplet collection has not been studied up to now. The present paper addresses this problem from a computational fluid dynamics perspective, where three-dimensional numerical simulations are used to characterize the fog flow properties around a simplified geometry mimicking the beetle's body. The simulations employ two-way coupling between the gas flow and the dispersed fog phase to account for feedback effects of fog droplets on the carrier fluid (air), and assume that droplets are captured after hitting the elytron surface. The study considers several combinations of free-stream velocity and droplet volume fraction. The analysis reveals that there is a range of head-stance angles, corresponding to an inclination of the beetle between 35 deg and 45 deg with respect to the horizon, that maximizes water collection on the beetle's back, in qualitative agreement with observations in nature and laboratory experiments. A rationale is proposed to explain this phenomenon, finding that the specific head stance corresponds to the maximum residence time of fluid particles above the beetle's elytron surface. This, in turn, designates the maximum likelihood for water droplets to be captured in the boundary layer developing over the beetle and subsequently hit the surface where they get captured. The results reveal the importance of the fluid flow pattern around the beetle's body in addition to the microphysical properties of the elytron when reliable predictions of the water droplet collection efficiency are sought.