AI 中文总结
该研究以平板为对象，建立尾流捕获最小模型，揭示翼-尾流相互作用机制，发现反转前移动距离对阻力峰值及尾流作用力衰减的影响规律。
AI 中文摘要
在类似往复扑动的运动中，翼-尾流相互作用对流体力的产生起着至关重要的作用。尽管该效应的存在已被认可，尤其用于解释测量力与准稳态近似之间的差异，但对该相互作用背后机制及其尺度规律的基础研究仍有限。为解决这一问题，我们研究了平板在前后平移运动反转阶段所受的、相对于准稳态估计值的额外阻力。该运动产生的流动在与昆虫飞行相关的雷诺数下被研究，作为生物扑动的简化类比。我们证明，与预先存在的尾流流动的相互作用确实会产生额外阻力。控制该相互作用的主要参数是反转前的移动距离，它影响阻力峰值的大小和时间动态。我们将观测结果与最优涡形成联系起来，因为反转期间额外阻力的时间轨迹会被启动涡环的分离定性改变：涡分离和再形成导致两个不同的尾流-力峰值。此外，随着反转前移动距离的增加，反转后尾流相互作用力的衰减更慢。流动观测显示，反转时刻尾流中流向速度的空间衰减类似，表明存在直接联系。将启动涡表示为点涡表明，尾流的空间尺度以及相应的翼-尾流相互作用效应的时间尺度，主要由涡环的位置、形状和环量决定。这种简化揭示了对反转前平移距离的依赖，可通过四次方根与线性尺度的组合来描述。
英文摘要
In reciprocating flapping-like motions, wing-wake interaction plays a crucial role in fluid force generation. While this effect's existence has been acknowledged, particularly in explaining discrepancies between measured forces and quasi-steady approximations, fundamental research on the mechanism underlying this interaction and its scaling remains limited. To address this, we investigate the excess drag force, relative to quasi-steady estimates, acting on a flat plate during the reversal phase of a forward and back translational motion. The flow produced by this motion, studied at insect-flight-relevant Reynolds numbers, serves as a simplified analogue to biological flapping. We demonstrate that interaction with pre-existing wake flow indeed generates excess drag. The main parameter governing this interaction is the distance travelled before reversal, which influences both magnitude and temporal dynamics of the peak drag. We link our observations to optimal vortex formation, as the time trace of the additional drag during reversal is qualitatively altered by the detachment of the starting vortex ring: vortex detachment and re-formation lead to two distinct wake-force peaks. Furthermore, as the pre-reversal distance traversed increases, the wake interaction force post-reversal decays more slowly. Flow observations reveal a similar spatial decay of the streamwise velocity in the wake at the moment of reversal, suggesting a direct link. Representing the starting vortex as a point vortex indicates that the wake's spatial scaling, and commensurately the temporal scaling of the wing-wake interaction effect, is primarily governed by the vortex ring position, shape, and circulation. This simplification reveals a dependence on the pre-reversal translation distance that can be described by a combined fourth-root and linear scaling.
