Bruecker Christoph H, Mikulich Vladimir
Department of Mechanical Engineering and Aeronautics, City, University of London, London, United Kingdom.
Institute of Mechanics and Fluid Dynamics, TU Bergakademie Freiberg, Freiburg, Germany.
PLoS One. 2017 Jun 28;12(6):e0179253. doi: 10.1371/journal.pone.0179253. eCollection 2017.
This work describes the development and use of pappus-like structures as sensitive sensors to detect minute air-flow motions. We made such sensors from pappi taken from nature-grown seed, whose filiform hairs' length-scale is suitable for the study of large-scale turbulent convection flows. The stem with the pappus on top is fixated on an elastic membrane on the wall and tilts under wind-load proportional to the velocity magnitude in direction of the wind, similar as the biological sensory hairs found in spiders, however herein the sensory hair has multiple filiform protrusions at the tip. As the sensor response is proportional to the drag on the tip and a low mass ensures a larger bandwidth, lightweight pappus structures similar as those found in nature with documented large drag are useful to improve the response of artificial sensors. The pappus of a Dandelion represents such a structure which has evolved to maximize wind-driven dispersion, therefore it is used herein as the head of our sensor. Because of its multiple hairs arranged radially around the stem it generates uniform drag for all wind directions. While still being permeable to the flow, the hundreds of individual hairs on the tip of the sensor head maximize the drag and minimize influence of pressure gradients or shear-induced lift forces on the sensor response as they occur in non-permeable protrusions. In addition, the flow disturbance by the sensor itself is limited. The optical recording of the head-motion allows continuously remote-distance monitoring of the flow fluctuations in direction and magnitude. Application is shown for the measurement of a reference flow under isothermal conditions to detect the early occurrence of instabilities.
这项工作描述了类冠毛结构作为灵敏传感器来检测微小气流运动的开发与应用。我们用从自然生长的种子上获取的冠毛制作了此类传感器，其丝状毛发的长度尺度适合用于研究大规模湍流对流。顶部带有冠毛的茎固定在壁上的弹性膜上，并在风荷载作用下倾斜，倾斜程度与风向的速度大小成正比，这与蜘蛛身上发现的生物传感毛发类似，不过在此处传感毛发尖端有多个丝状突起。由于传感器响应与尖端所受阻力成正比，且低质量确保了更大的带宽，与自然界中具有较大记录阻力的冠毛结构类似的轻质冠毛结构有助于改善人工传感器的响应。蒲公英的冠毛就代表了这样一种结构，它经过进化以实现风驱动扩散的最大化，因此在此处用作我们传感器的头部。由于其数百根毛发围绕茎径向排列，它在所有风向都能产生均匀的阻力。虽然对气流仍具有渗透性，但传感器头部尖端的数百根单独毛发使阻力最大化，并将压力梯度或剪切诱导升力对传感器响应的影响降至最低，而这些影响在非渗透性突起中会出现。此外，传感器本身对气流的干扰有限。头部运动的光学记录允许对气流波动的方向和大小进行连续的远程监测。展示了其在等温条件下测量参考气流以检测不稳定性早期发生情况的应用。
