Danis Umit, Rasooli Reza, Chen Chia-Yuan, Dur Onur, Sitti Metin, Pekkan Kerem
Department of Mechanical Engineering, Carnegie Mellon University, Pittsburgh, PA 15213, USA.
Department of Mechanical Engineering, Koc University, Istanbul 34450, Turkey.
Micromachines (Basel). 2019 Jul 4;10(7):449. doi: 10.3390/mi10070449.
The motility mechanism of prokaryotic organisms has inspired many untethered microswimmers that could potentially perform minimally invasive medical procedures in stagnant fluid regions inside the human body. Some of these microswimmers are inspired by bacteria with single or multiple helical flagella to propel efficiently and fast. For multiple flagella configurations, the direct measurement of thrust and hydrodynamic propulsion efficiency has been challenging due to the ambiguous mechanical coupling between the flow field and mechanical power input. To address this challenge and to compare alternative micropropulsion designs, a methodology based on volumetric velocity field acquisition is developed to acquire the key propulsive performance parameters from scaled-up swimmer prototypes. A digital particle image velocimetry (PIV) analysis protocol was implemented and experiments were conducted with the aid of computational fluid dynamics (CFD). First, this methodology was validated using a rotating single-flagellum similitude model. In addition to the standard PIV error assessment, validation studies included 2D vs. 3D PIV, axial vs. lateral PIV and simultaneously acquired direct thrust force measurement comparisons. Compatible with typical micropropulsion flow regimes, experiments were conducted both for very low and higher Reynolds (Re) number regimes (up to a Re number = 0.01) than that are reported in the literature. Finally, multiple flagella bundling configurations at 0°, 90° and 180° helical phase-shift angles were studied using scaled-up multiple concentric flagella thrust elements. Thrust generation was found to be maximal for the in-phase (0°) bundling configuration but with ~50% lower hydrodynamic efficiency than the single flagellum. The proposed measurement protocol and static thrust test-bench can be used for bio-inspired microscale propulsion methods, where direct thrust and efficiency measurement are required.
原核生物的运动机制启发了许多无系绳微型游泳器，这些微型游泳器有可能在人体内部的停滞流体区域执行微创医疗程序。其中一些微型游泳器的灵感来自具有单个或多个螺旋鞭毛的细菌，能够高效快速地推进。对于多个鞭毛配置，由于流场与机械动力输入之间的机械耦合不明确，直接测量推力和流体动力推进效率一直具有挑战性。为了应对这一挑战并比较替代的微推进设计，开发了一种基于体积速度场采集的方法，以从放大的游泳器原型中获取关键的推进性能参数。实施了数字粒子图像测速（PIV）分析协议，并借助计算流体动力学（CFD）进行了实验。首先，使用旋转单鞭毛相似模型对该方法进行了验证。除了标准的PIV误差评估外，验证研究还包括二维与三维PIV、轴向与横向PIV以及同时获取的直接推力测量比较。与典型的微推进流态兼容，实验在比文献报道的更低和更高雷诺数（Re）范围（高达Re数 = 0.01）下进行。最后，使用放大的多个同心鞭毛推力元件研究了在0°、90°和180°螺旋相移角下的多个鞭毛束配置。发现同相（0°）束配置的推力最大，但流体动力效率比单鞭毛低约50%。所提出的测量协议和静态推力试验台可用于需要直接测量推力和效率的生物启发式微尺度推进方法。
