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Pressure gradient in channel flow - mapped BC

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Old   September 7, 2012, 13:34
Default Pressure gradient in channel flow - mapped BC
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Hi!!

I want to simulate a simple channel flow with periodic boundary contidions in the inlet/outlet. If I understand correctly I have two ways of doing it:

Option 1: Use channelFoam and the solver will verify the mass flow rate.

Option 2: Use pisoFoam solver instead with the mapped (directMapped in previous OF versions) boundary conditions with "setAverage true" for the velocity. The code is also verify and correct the mass flow rate.

Is that correct? Are there any diferences between the two options?

Does it mean that by using a "mapped boundary" conditions I am imposing a pressure gradient in that direction?

Thanks in advance...
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Old   February 15, 2013, 14:35
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Quote:
Originally Posted by MaryBau View Post
Hi!!

I want to simulate a simple channel flow with periodic boundary contidions in the inlet/outlet. If I understand correctly I have two ways of doing it:

Option 1: Use channelFoam and the solver will verify the mass flow rate.

Option 2: Use pisoFoam solver instead with the mapped (directMapped in previous OF versions) boundary conditions with "setAverage true" for the velocity. The code is also verify and correct the mass flow rate.

Is that correct? Are there any diferences between the two options?

Does it mean that by using a "mapped boundary" conditions I am imposing a pressure gradient in that direction?

Thanks in advance...
Same question, how to add pressure gradient.
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Old   February 19, 2013, 17:41
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I tried two cases:

1) mapped boundary conditions (or directMapped in older versions) in the inlet/outlet with a "setAverage true" and using the regular OF pisoFoam (no pressure gradient).

2) having a pressure gradient added to the pisoFoam UEqn and cyclic inlet/outlet boundary conditions.

and I obtained the same results in both cases.

Now, to add a pressure gradient to drive the flow, you have to modified the UEqn in pisoFoam.

Code:
fvVectorMatrix UEqn
            (
                fvm::ddt(U)
              + fvm::div(phi, U)
              + turbulence->divDevReff(U)
              + gradP
            );
where

Code:
    dimensionedVector gradP
    (
        "gradP",
        dimensionSet(0, 1, -2, 0, 0),
        vector::zero
    );
Hope it helps!
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Old   February 26, 2013, 16:30
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Hi MaryBau.
Thanks very much! In code:
Code:
    dimensionedVector gradP
    (
        "gradP",
        dimensionSet(0, 1, -2, 0, 0),
        vector::zero
    );
Why did you set the gradP=0? Since there is no pressure gradient, how to drive the flow?
I am a new user of openFoam.....

Quote:
Originally Posted by MaryBau View Post
I tried two cases:

1) mapped boundary conditions (or directMapped in older versions) in the inlet/outlet with a "setAverage true" and using the regular OF pisoFoam (no pressure gradient).

2) having a pressure gradient added to the pisoFoam UEqn and cyclic inlet/outlet boundary conditions.

and I obtained the same results in both cases.

Now, to add a pressure gradient to drive the flow, you have to modified the UEqn in pisoFoam.

Code:
fvVectorMatrix UEqn
            (
                fvm::ddt(U)
              + fvm::div(phi, U)
              + turbulence->divDevReff(U)
              + gradP
            );
where

Code:
    dimensionedVector gradP
    (
        "gradP",
        dimensionSet(0, 1, -2, 0, 0),
        vector::zero
    );
Hope it helps!
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channelfoam, mappedfixedvalue, pisofoam, pressure gradient

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