We describe a simple classroom demonstration of a fluid-dynamic instability. The demonstration requires only a bucket of water, a piece of string and some used tealeaves or coffee grounds. We argue that the mechanism for the instability, at least in its later stages, is two-dimensional barotropic (shear-flow) instability and we present evidence in support of this. We show results of an equivalent basic two-dimensional numerical non-linear model, which simulates behavior comparable to that observed in the bucket demonstration. Modified simulations show that the instability does not depend on the curvature of the domain, but rather on the velocity profile.

中文翻译：

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剪切流不稳定性的简单演示

我们描述了流体动力学不稳定性的简单课堂演示。演示只需要一桶水、一根绳子和一些用过的茶叶或咖啡渣。我们认为，至少在后期阶段，不稳定的机制是二维正压（剪切流）不稳定，我们提供了支持这一点的证据。我们展示了等效的基本二维数值非线性模型的结果，该模型模拟了与桶演示中观察到的行为相当的行为。修改后的模拟表明，不稳定性不取决于域的曲率，而是取决于速度剖面。