Measurements are presented of the drag force on several different balls falling vertically through water in a fish tank, at speeds up to 4.5 m/s. Experiments of this type are usually undertaken in a student laboratory by measuring the terminal velocity of an object falling either through air or a viscous liquid. At speeds slightly higher than the terminal velocity, additional effects can be observed visually in water, including flow separation and turbulent flow. Changes in the drag coefficient were observed due to both effects, although different changes were observed with different balls, resulting from the formation of an air cavity behind each ball. Cavity formation was found to depend strongly on the roughness of the ball surface as well as the incident ball speed. Results are presented at Reynolds numbers from about 20,000 up to about 250,000.

中文翻译：

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水中球阻力的测量

在鱼缸中以高达 4.5 m/s 的速度垂直落入水中的几个不同球上的阻力测量值。这种类型的实验通常在学生实验室中进行，通过测量物体在空气或粘性液体中落下的终端速度。在速度略高于终端速度时，可以在水中肉眼观察到额外的影响，包括流动分离和湍流。由于这两种效应，都观察到阻力系数的变化，尽管观察到不同的球发生了不同的变化，这是由于每个球后面形成的空气腔造成的。发现腔的形成很大程度上取决于球表面的粗糙度以及入射球速度。结果以雷诺数表示，从约 20,000 到约 250，