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Velocity increases when fluid approaches outlet

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Old   May 14, 2015, 18:30
Default Velocity increases when fluid approaches outlet
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Leonardo
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Hello there,

I'm trying to figure out why I'm getting these results. Due to pressure drop along the flow channel, shouldn't the velocity only decrease? Why is my fluid velocity increasing when approaching outlet?

Inlet BC is a specified velocity.
Outlet BC is average static pressure set to 0 Pa relative pressure.

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Old   May 14, 2015, 18:35
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You may need to provide more details.

For example, is the fluid incompressible, or compressible. For incompressible fluid with specified inlet velocity, and uniform cross section, the velocity at the outlet will be higher than the inlet away from the walls, but the net mass flow will be the same as the inlet (conservation of mass). It is not a function of the pressure drop.

Hope I made sense above,
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Old   May 14, 2015, 18:41
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Quote:
Originally Posted by Opaque View Post
You may need to provide more details.

For example, is the fluid incompressible, or compressible. For incompressible fluid with specified inlet velocity, and uniform cross section, the velocity at the outlet will be higher than the inlet away from the walls, but the net mass flow will be the same as the inlet (conservation of mass). It is not a function of the pressure drop.

Hope I made sense above,
Thanks for the response!

It's an incompressible fluid, a solution of ethanol+water. The cross section is indeed uniform throughout the flow channel. Isothermic model.
There's some transport at the -Z direction, where there's a porous material, but I don't think that should affect much the flow at the presented flow channel.
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Old   May 15, 2015, 10:16
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Alright, I might have found the answer.

It was simply because there's only one outlet in my model, so the ethanol that goes through the porous layers below the flow channel has to go back to the channel in order to leave the domain.

I confirmed this by checking the 'velocity w' profiles.
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