We computationally studied the kinematics of a simple reciprocal model swimmer (asymmetric dumbbell) in a Newtonian fluid as a function of the Reynolds number (Re), and investigated how the onset and gradual increase of inertia impacts swimming behavior: a reversal in the swim direction, flow field, and the swim stroke. We divided the swim stroke into the increase and decrease in the distance between the two spheres (expansion and compression respectively) and related them to power and recovery strokes. We found that the switch in swim direction also corresponds to a switch in power and recovery strokes. We obtained expressions for the mean swimming velocity by collapsing the net displacement during expansion and compression under power-law relationships with respect to Re, the swimmer's amplitude, and the distance between the two spheres. Analyzing the fluid flows, we saw that the averaged flow field during expansion always resembles a pusher and during compression it always resembles a puller, but when averaged over the whole cycle, the flow that dominates is the one that occurs during the power stroke. We also related the power and recovery strokes to the swimming efficiency during times of expansion and compression, and found that the power stroke is, surprisingly, not always more efficient than the recovery stroke. Our results may have important implications in biology and ultimately the design of artificial swimmers.

中文翻译：

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一个简单的倒数模型游泳者在雷诺数中间的运动学

我们通过计算研究了简单倒数模型游泳者（非对称哑铃）在牛顿流体中的运动学特性，该函数是雷诺数（Re）的函数，并研究了惯性的开始和逐渐增加如何影响游泳行为：游泳方向的反转，流场和游泳行程。我们将游泳冲程分为两个球体之间的距离的增加和减少（分别为扩张和压缩），并将它们与力量和恢复冲程相关联。我们发现，游泳方向上的开关也对应于力量和恢复冲程的开关。我们通过收缩相对于Re，游泳者的振幅和两个球体之间的距离的幂律关系下的膨胀和压缩过程中的净位移来获得平均游泳速度的表达式。分析流体流动，我们发现膨胀期间的平均流场始终类似于推动器，而压缩期间的平均流场始终类似于牵引器，但是在整个周期中进行平均时，占主导地位的流场就是动力冲程期间发生的流场。我们还将力量和恢复冲程与膨胀和压缩期间的游泳效率相关联，发现令人惊讶的是，力量冲程并不总是比恢复冲程更有效。我们的结果可能会对生物学产生重要影响，并最终对人工游泳运动员的设计产生影响。主导流是在动力冲程期间发生的。我们还将力量和恢复冲程与膨胀和压缩期间的游泳效率相关联，发现令人惊讶的是，力量冲程并不总是比恢复冲程更有效。我们的结果可能会对生物学产生重要影响，并最终对人工游泳运动员的设计产生影响。主导流是在动力冲程期间发生的。我们还将力量和恢复冲程与膨胀和压缩期间的游泳效率相关联，发现令人惊讶的是，力量冲程并不总是比恢复冲程更有效。我们的结果可能会对生物学产生重要影响，并最终对人工游泳运动员的设计产生影响。