Binary droplet collisions exhibit a wide range of outcomes, including coalescence and stretching separation, with a transition between these two outcomes arising for high Weber numbers and impact parameters. Our experimental study elucidates the effect of viscosity on this transition, which we show exhibits inertial (viscosity-independent) behaviour over an order-of-magnitude-wide range of Ohnesorge numbers. That is, the transition is not always shifted towards higher impact parameters by increasing droplet viscosity, as it might be thought from the existing literature. Moreover, we provide compelling experimental evidence that stretching separation only arises if the length of the coalesced droplet exceeds a critical multiple of the original droplet diameters (3.35). Using this as a criterion, we provide a simple but robust model (without any arbitrarily chosen free parameters) to predict the coalescence/stretching-separation transition.

中文翻译：

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二元液滴碰撞中的惯性拉伸分离

二元液滴碰撞表现出广泛的结果，包括聚结和拉伸分离，这两种结果之间的过渡是由于高韦伯数和冲击参数而产生的。我们的实验研究阐明了粘度对这种转变的影响，我们展示了在 Ohnesorge 数的数量级范围内表现出惯性（与粘度无关）行为。也就是说，转变并不总是通过增加液滴粘度而向更高的冲击参数转移，正如现有文献中可能认为的那样。此外，我们提供了令人信服的实验证据表明，只有当聚结液滴的长度超过原始液滴直径的临界倍数 (3.35) 时，才会出现拉伸分离。以此为标准，