Vortex generated by a swirl at the bottom

Let's take a look!

What type of experiment is this?

Experimental procedure and explanation:

• We use a stirrer to swirl the water in the container.
• We can then add the torn tissue paper to observe the flow of water. The tissue paper then moves down along the center of the vortex. This shows that the flow is facing downward at the center of the vortex. We can also see that the flow is rotating faster near the center than at the periphery (a flow similar to a free vortex).
• The water is forced to rotate faster by the rotor near the bottom of the tank. Therefore, it can be seen that the apparent centrifugal force seen from the water is also greater, and the water flows outward as it rotates.
• To replenish this displaced water, the water at the top moves in the downward direction. This causes a downward flow on the centerline of the vortex, moving outward at the bottom rising along the inner surface of the container, and a circulating flow moving inward at the top. This circulating flow will be a component of the flow perpendicular to the swirling flow (called the main flow, because it is the main actor in this phenomenon). This flow component perpendicular to the main flow is called the secondary flow.
• In the vortex given a swirl at the bottom, we see that a downward secondary flow occurs on the centerline of the vortex.
• This experimental video was produced with the support of JSPS Grant-in-Aid for Scientific Research 18K03956.

[Keywords]	Vortex, secondary flow
[Related items]	Vortex generated by a swirl at the top, Free Vortex and Forced Vortex, Centrifugal Force
[Reference]	Ryozo Ishiwata, "The Wonder of Flow," Kodansha Blue Backs, p. 52-61.

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