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Reynolds number in pressure driven flow

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Old   October 1, 2013, 12:41
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Liam
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Anybody knows how to compute Reynolds number for a pressure driven flow? I have read something in the fórum about Bernouilli and mass conservation, but I am not sure if this can be used for obtaining the velocity for Reynolds number calculations...

I have two inlets, a wall and one outlet. I guess characteristic lenght is hydraulic diameter, but if I had two inlets, should I use as lenght the sum of the hydraulic dyameter of both inlets?

Sorry for that stupid questions, sure somebody can answer it easily...

Thanks!
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Old   October 1, 2013, 13:00
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Filippo Maria Denaro
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Originally Posted by Many View Post
Anybody knows how to compute Reynolds number for a pressure driven flow? I have read something in the fórum about Bernouilli and mass conservation, but I am not sure if this can be used for obtaining the velocity for Reynolds number calculations...

I have two inlets, a wall and one outlet. I guess characteristic lenght is hydraulic diameter, but if I had two inlets, should I use as lenght the sum of the hydraulic dyameter of both inlets?

Sorry for that stupid questions, sure somebody can answer it easily...

Thanks!

You just have two characteristic Reynolds numbers, each for inlet of diameter D1 and D2. The viscosity is the same. Just need to know the two velocities. If you are using a computation with non-dimensional variable, use the characteristic diameter and velocity that characterize your flow.
Note also that the Reynolds number is also a local variable as it depends on the developping of the boundary layer along the wall
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