Flow in a Curved River that is Shallower on the Inside

Let's take a look!

Watch the video on YouTube.

What type of experiment is this?

Experimental procedure and explanation:

• In an actual river, the inner side is shallower because sediment is deposited on the inside. In this experiment, we made the inner side shallower to more accurately simulate a real river.
• The flow speed is slower at the shallow inner part.
• Up to a certain depth, we can see a tendency for the flow at the outside to be slower and the flow at the inside to be faster. This is the same as the situation described in “Speed of Flow in a Curved River,” in which the water had a uniform depth.
• At a certain depth, the flow near the bottom is slow and the centrifugal force is small, and therefore the flow near the bottom is pushed by the high pressure on the outside, creating an inward flow. Towards the top where the centrifugal force is larger, an outward flow is generated, resulting in secondary flow, as shown by the red line in the figure. (In fluid dynamics, when considering flow at a curve or a rotating flow, we often observe the phenomena of rotation from the perspective of the fluid particles. We will explain the operating principle in this experiment in this way, using apparent force and centrifugal force.)
• Particles of earth and sand that sink in the water are carried to the sides of the river and deposited there by this secondary flow. Compared to the case with the uniform depth of water (Sediment in a Curved River), the flow is slower at the shallow part on the inner side, and therefore the sediment is deposited more easily.

[Keywords]	Swirl flow, Secondary flow
[Related items]	Speed of Flow in a Curved River, Sediment in a Curved River, Collecting Tea Leaves, Centrifugal Force
[Reference]	“The Wonders of Flow,” Japan Society of Mechanical Engineering, Kodansha Blue Backs, P60・・1.