Video Transcript
A fluid flows through a pipe that
decreases and then increases in thickness. In which of the regions shown would
the flow be more likely to become turbulent? (A) Region 1, (B) region 2, or (C)
the flow is equally likely to become turbulent in both regions.
We are asked in which region the
fluid is most likely to become more turbulent. So, to decide this, we first
remember that a fluid flowing in nice smooth sheets is said to undergo laminar
flow. This is shown by diagram A. However, if the layers of fluid are
chaotic and end up crossing each other and mixing, then the fluid is undergoing
turbulent flow. And this is shown by diagram B.
So the question asks us to look at
the diagram and figure out which of the regions, 1 or 2, is more likely to have
turbulent flow. Now, in the diagram, we can see
blue arrows representing the layers of the fluid, which is laminar because we see
individual parallel layers. We can also see that the fluid is
flowing from left to right. As the fluid approaches region 1,
it is being forced into a smaller region of space as the pipe narrows.
Now, it’s possible the flow will
become chaotic and turbulent here. But this would only happen if the
fluid was flowing very fast from left to right. If the fluid is flowing slowly,
it’s possible for the layers of the fluid to not mix chaotically as they flow into
the smaller region of the pipe. However, when the fluid flows
through the smaller part of the pipe, it will have to flow much quicker to ensure
the same amount of fluid flows from left to right in this smaller volume. We can also combine this with the
fact that the pipe widens again in region 2, meaning the fluid could flow in one of
many different directions. This means that the flow is much
more likely to be turbulent in region 2.
Hence, our final answer is option
(B). The flow is more likely to become
turbulent in region 2.
