Propulsion efficiency of bodies appended with multiple flapping fins: When more is less
Propulsion efficiency of bodies appended with multiple flapping fins: When more is less
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DOI：
10.1063/1.4802495
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发表时间：
2013-04-01
影响因子：
4.6
通讯作者：
Leinhos, Henry A.
中科院分区：
文献类型：
--
作者：
Bandyopadhyay, Promode R.;Leinhos, Henry A.
水下动物通过在一个狭窄的频率范围内拍打胸鳍和尾鳍来推进自己，这个频率范围由Strouhal数St给出，以产生过渡涡流射流（St通常以无量纲的方式表示为拍打频率和行程（弧）长度除以前进速度的乘积）。尽管确切的机制尚不清楚，但人们认为选择St和涡流射流的组织性质可使流体动力学效率最大化。我们最近的Stuart-Landau方程模型，具有自调节特性，表明鳍和它的射流涡耦合。在单一孤立的鳍的力的时间图显示在一定范围内的过渡雷诺数的双峰行为，这种行为具有相似的神经分叉特性，欠其起源的自我调节机制。鉴于我们的理论和biorobotic证据的自我调节，在单扑鳍，我们探讨，如果这种属性是在一个鳍附加机构改变，目标是了解如何狭窄的选择圣，自我调节，最大化的水动力效率相关。已经建造了1米规模的游泳车辆，其中刚性圆柱体附加有六个扑翼，每端三个。鳍是刚性的，有一个圆形的前缘和层流截面（NACA 0012），并在一端铰接。平面形状是企鹅翼的抽象版本;它具有低展弦比和在10000至60000的过渡范围内变化的弦雷诺数。鳍的几何形状，雷诺数范围，和非柔性的性质的主体是在共同的企鹅，和长度和位移量是类似的鲨鱼。附加鳍体的最大水动力效率（0.40）低于单个鳍体的最大水动力效率（0.57），但接近使用多个鳍体的鱼的最大水动力效率。附加鳍的圆柱体的推进密度（kW/m（3）的排量体积）与巡航鲨鱼的推进密度相似。如果我们允许比较电测量和热测量，附加鳍的机身的总效率与同样基于涡流推进的豆娘和蜻蜓的总效率相似。鳍力波动由一个货车der Pol振荡器模拟。测得的力波动与其时间导数的相位图与斯特劳哈尔数。直到稳定，最大的流体动力学效率的鳍附加机构增加鳍雷诺数在一个阶梯模式，其边界与类似的过渡子制度，在单鳍，包括双峰子制度，从而与效率的自我调节射流涡流振荡器。在低雷诺数，流体动力效率的峰值保持平坦，在很宽的范围内的ST，变得陡峭，在较高的雷诺数与最大值发生在较低的ST值的建模表明，自我调节，未来的生物机器人的设计应侧重于减少结构阻尼和鳍体组件，具有互惠的能量相互作用与脱落的涡流。[http：//dx.doi.org/10.1063/1.4802495]
Underwater animals propel themselves by flapping their pectoral and caudal fins in a narrow range of frequencies, given by Strouhal number St, to produce transitional vortex jets (St is generally expressed non-dimensionally as the product of flapping frequency and stroke (arc) length divided by forward speed). The organized nature of the selection of St and of the vortex jet is thought to maximize hydrodynamic efficiency, although the exact mechanism is not known. Our recent Stuart-Landau equation models, which have self-regulation properties, indicate that the fin and its jet vortices couple. Temporal maps of forces in single isolated fins show a bimodal behavior in certain ranges of the transitional Reynolds number; this behavior bears resemblance to neural bifurcation properties that owe their origin to the self-regulation mechanism. In view of our theoretical and biorobotic evidence of self-regulation in single flapping fins, we explore if this property is altered in a fin-appended body, the goal being to understand how the narrow selection of St, self-regulation, and maximization of hydrodynamic efficiency are related. Swimming vehicles of 1-m scale have been built where a rigid cylindrical body is appended with six flapping fins, three at each end. The fins are rigid, have a rounded leading edge and a laminar section (NACA 0012), and are hinged at one end. The planform is an abstracted version of the penguin wing; it has low aspect ratio and a chord Reynolds number that varies in the transitional range from 10 000 to 60 000. The fin geometry, Reynolds number range, and the nonflexible nature of the main body are in common with those in penguins, and the length and displacement volume are similar to those of sharks. The maximum hydrodynamic efficiency of the fin-appended body (0.40) is lower than that of the single fin (0.57), but is close to that of a fish using several fins. The propulsion density (kW/m(3) of displacement volume) of the fin-appended cylinder is similar to that of a cruising shark. If we allow comparison of electrical versus thermal measurements, the total efficiency of the fin-appended body is similar to that of the damselfly and dragonfly, which are also based on vortex propulsion. The fin force fluctuations are modeled by a van der Pol oscillator. Measured phase maps of force fluctuation versus its time derivative correlate with the Strouhal numbers. Until stabilization, the maximum hydrodynamic efficiency of the fin-appended body increases with fin Reynolds number in a staircase pattern whose boundaries correlate with similar transitional sub-regimes in single fins, including the bimodal sub-regimes, thereby relating efficiency with the self-regulating jet vortex oscillators. At low Reynolds numbers, the peak of hydrodynamic efficiency remains flat over a wide range of St, becoming steeper at higher Reynolds numbers with the maximum occurring at lower values of St. The modeling shows that for self-regulation, future biorobotic design should focus on the reduction of structural damping and on a fin-body assembly that has reciprocal energetic interaction with the shed vortex. [http://dx.doi.org/10.1063/1.4802495]