通过蟹足的杯状调节实现流体动力学调节
Hydrodynamic modulation via cupping in a crustacean-inspired propulsor
AI总结：
研究通过调节蟹足的杯状角度，发现适度角度可优化推力-升力平衡，揭示了虾足作为混合推进器的机制。
摘要：
虾，像许多在中间雷诺数（Re）下游泳的无脊椎动物一样，依赖于形态和运动学之间的相互作用来产生推力，同时产生足够的升力以克服其负浮力。虾的 Pleopods 分裂成一个内端足和一个外端足，它们的相对运动在游泳周期中改变投影表面积。为了使这种机制发挥作用，外端足必须相对于内端足在设定的杯状角度ζ下弯曲，这在一定程度上将外端足的有效攻角与整体腿部运动学部分解耦。在这里，我们研究了ζ在稳态前向运动中调节推力-升力平衡中的作用。使用一个动态缩放（40倍）的机械 Pleopod，我们系统地改变了ζ从0°到80°，测量了水动力学力，并在Re=968下进行了粒子图像测速。适度的杯状角度（ζ=20°-40°），与生物观察一致，提供了最佳的推力-升力平衡。在这些角度下，外端足在动力冲程中迅速 abduction，最大化峰值流速时的投影面积，并在回冲冲程中早期 adduct，最小化阻力拖曳。一个降阶力模型表明，外端足贡献了总升力的52%-62%，特别是在中间ζ下，当leading-edge vortex（LEV）形成并保持附着在整个动力冲程中。在极端杯状角度下，LEV的相干性降低，力的产生减弱。这些发现表明，虾的 Pleopods 作为混合推进器，利用了基于阻力和升力的力，且ζ作为几何控制参数，能够独立于冲程运动学调节推力-升力平衡。
英文摘要：
Shrimp, like many invertebrates swimming at intermediate Reynolds numbers ($Re$), rely on the interplay between morphology and kinematics to generate thrust while producing sufficient lift to overcome their negative buoyancy. Shrimp pleopods branch into an endopodite and an exopodite, whose relative motion varies the projected surface area during the swimming cycle. For this mechanism to function, the exopodite must be cambered relative to the endopodite at a set cupping angle $ζ$, which partially decouples the effective angle of attack of the exopodite from the overall leg kinematics. Here, we investigate the role of $ζ$ in modulating thrust$-$lift balance during steady forward locomotion. Using a dynamically scaled (40$\times$) robotic pleopod, we systematically varied $ζ$ from $0^\circ$ to $80^\circ$, measured hydrodynamic forces, and performed particle image velocimetry at $Re = 968$. Moderate cupping angles ($ζ= 20^\circ-40^\circ$), consistent with biological observations, provide optimal thrust$-$lift balance. At these angles, the exopodite abducts rapidly during the power stroke, maximizing projected area at peak flow velocity, and adducts early during the return stroke, minimizing resistive drag. A reduced-order force model reveals that the exopodite contributes 52$-$62\% of total lift, particularly at intermediate $ζ$, where a leading-edge vortex (LEV) forms and remains attached throughout the power stroke. At extreme cupping angles, LEV coherence degrades and force production weakens. These findings demonstrate that shrimp pleopods function as hybrid propulsors exploiting both drag- and lift-based forces, and that $ζ$ serves as a geometric control parameter capable of tuning thrust$-$lift balance independently of stroke kinematics.
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