| Great Mysteries of Engineering Fluid Dynamics
The Fate of the Sinking Tea Leaves |
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One of the realities of the flow of fluids found in most industrial settings, is that the flow patterns and physics are much more complex than those of the model flows presented in undergraduate texts on engineering fluid mechanics. The story that follows gives you an opportunity to increase your ability to understand and control these complex fluid flows. The story is presented as a mystery which is unraveled as the story progresses. The unraveling of the mystery will involve an exploration of actual flows that can be easily set up and virtual flow fields obtained by computer simulation using computational fluid dynamics (CFD) technology.
The presentation of the mystery has been designed to give ample opportunity for you to solve the mystery by exploring the flow fields. Take the time to see all of the features in each flow and to identify the relevant flow
kinematics, forces, and dynamics.
Best wishes for an enjoyable learning experience.
Synopsis
Tea leaves are added to a beaker of still cold water. As the leaves get soggy, they begin to sink to the bottom of the beaker. This indicates that the tea leaves are heavier than water. After most of the leaves have sunk to the bottom, the water in the beaker is stirred in either a clockwise or counter-clockwise direction. Where will the leaves on the bottom of the beaker collect - near the outer wall or near the middle?
Those of you that set up this simple flow will notice that the tea leaves tend to move towards the middle of the beaker. Why doesn't centrifugal action throw the leaves towards the outer wall?
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