On the mixing of angular momentum in a stirred rotating fluid
On the mixing of angular momentum in a stirred rotating fluid
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关于搅拌旋转流体中角动量的混合
DOI：
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发表时间：
1968
影响因子：
3.7
通讯作者：
J. S. Turner
中科院分区：
文献类型：
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作者：
F. Bretherton;J. S. Turner
理论上有人认为，在圆柱形流体区域中，由于外部搅拌产生的角动量的水平混合，可以在最初的固体旋转中产生涡流。在本文中，各种支持和反对该机制的论点进行审查，并暴露其困难。没有得出确切的结论。一系列的混合运动的数学模型已被使用，以带出机械搅拌和随机分子运动的气体搅拌之间的差异。他们建议引入角动量的扩散系数，由经验确定。这些理论的想法，然后应用到解释的实验室实验的结果，已被设计为直接测试所提出的机制。将宽的扁平液体罐设置在旋转台上，并用垂直振荡的格栅搅拌，格栅的元件比罐的宽度小得多。中性浮力粒子被用作流体运动的示踪剂，以测量相对循环速度和湍流的性质。观察到的运动主要是由角动量的损失的墙壁和网格，尚未考虑到在以前的理论评估的混合角动量的影响的效果。存在的相对环流与零没有显著差异，并且测量的误差极限意味着角动量的扩散率小于流体粒子的扩散率的5%，具有95%的概率。
It has been suggested on theoretical grounds that a vortex could be initiated in a cylindrical region of fluid, originally in solid rotation, by the horizontal mixing of angular momentum produced by external stirring. In this paper various arguments for and against the mechanism are examined and their difficulties exposed. No firm conclusion is reached. A series of mathematical models of the mixing motions has been used, to bring out the differences between mechanical stirring and the agitation of a gas by random molecular motions. They suggest the introduction of a diffusion coefficient for angular momentum, to be determined empirically. These theoretical ideas are then applied to the interpretation of the results of a laboratory experiment which has been designed to test the proposed mechanism directly. A wide, flat tank of liquid was set up on a rotating table and stirred with a vertically oscillated grid, whose elements were much smaller than the width of the tank. A neutrally buoyant particle was used as a tracer of fluid motions, to measure relative circulation velocities and the properties of the turbulence. The motion observed was dominated by the loss of angular momentum to the walls and the grid, an effect which has not been taken into account in previous theoretical assessments of the effects of mixing of angular momentum. The relative circulation present was not significantly different from zero, and the limits of error of the measurements imply that the rate of diffusion of angular momentum is less than 5% of that for fluid particles, with 95% probability.