- #1

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Greetings everyone,

I've been recently trying to calculate the forces acting on a stationary object in pipe with flowing fluid. I've returned to my college textbooks to get some help and I've found examples that clearly demonstrated how to accomplish just that.

Below is one example.

This example uses conservation of momentum principles for a simple incompressible, inviscid fluid which is what I'm looking for.

Now I've got to thinking.

If the plug in the example was reduced in diameter, then intuition tells me that the force to hold the plug stationary would be smaller.

So I tried using a smaller plug diameter in the formula but I got a larger force!

See the table below.

Keeping everything else the same, as the plug diameter decreases, the force to hold it in place increases.

It's either the author of the textbook has understood this calculated force incorrectly or this is actually real and my understanding of the world is wrong.

There is another example later in the textbook which is solved in the same method so it is not a one-off type or something.

Does anyone know what is happening here? And is the correct method to determine the force to keep a plug stationary in a pipe with flowing fluid?

Thanks,

I've been recently trying to calculate the forces acting on a stationary object in pipe with flowing fluid. I've returned to my college textbooks to get some help and I've found examples that clearly demonstrated how to accomplish just that.

Below is one example.

This example uses conservation of momentum principles for a simple incompressible, inviscid fluid which is what I'm looking for.

Now I've got to thinking.

If the plug in the example was reduced in diameter, then intuition tells me that the force to hold the plug stationary would be smaller.

So I tried using a smaller plug diameter in the formula but I got a larger force!

See the table below.

Keeping everything else the same, as the plug diameter decreases, the force to hold it in place increases.

It's either the author of the textbook has understood this calculated force incorrectly or this is actually real and my understanding of the world is wrong.

There is another example later in the textbook which is solved in the same method so it is not a one-off type or something.

Does anyone know what is happening here? And is the correct method to determine the force to keep a plug stationary in a pipe with flowing fluid?

Thanks,