# Reynolds number in pressure driven flow

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 October 1, 2013, 12:41 Reynolds number in pressure driven flow #1 Member   Liam Join Date: Aug 2013 Posts: 40 Rep Power: 6 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!

October 1, 2013, 13:00
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Filippo Maria Denaro
Join Date: Jul 2010
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Quote:
 Originally Posted by Many 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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