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ZeroGradient pressure Outlet BC prob (adjustPhi.C)

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Old   March 23, 2010, 06:52
Default ZeroGradient pressure Outlet BC prob (adjustPhi.C)
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Stylianos Kyriacou
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Hello Everyone

I've been trying to set-up a Rotor-Stator case for MRFSimpleFoam (my goal is to obtain an initial solution to then use with turbDyMFoam for an unsteady calculation).

I've succeeded on getting a converged solution via MRFSimpleFoam but i observed that i had a strange pressure distribution near the outlet (a pressure step exactly at the last nodes before the outlet). After some search in previous threads i found out that a good idea is to use zeroGradient (with pRefCell and pRefValue) as outlet BC.

My initial BCs were:
U:
INLET
{
type flowRateInletVelocity;
flowRate 0.750;
value uniform (0 0 0);
}
OUTLET
{
type inletOutlet;
value uniform (0 0 0);
inletValue uniform (0 0 0);
}

P:
INLET
{
type zeroGradient;
}
OUTLET
{
type fixedMeanValue;
meanValue 0;
}


My modified BCs are:
U
:
INLET
{
type flowRateInletVelocity;
flowRate 0.750;
value uniform (0 0 0);
}
OUTLET
{
type zeroGradient;
}

P:
INLET
{
type zeroGradient;
}
OUTLET
{
type zeroGradient;
}

but with the new BC set up (and although i initialized my U field with a sensible value) i get this error:

Continuity error cannot be removed by adjusting the outflow.
Please check the velocity boundary conditions and/or run potentialFoam to initialise the outflow.
Specified mass inflow : 0.75
Specified mass outflow : 0
Difference : 0.75
Adjustable mass outflow : 0

I've then went to adjustPhi.C to check out (maybe i was missing something) and i've seen that the part that calculates Specified mass outflow, Specified mass inflow and Adjustable mass outflow has undergone a recent bug fix (// HJ, 12/Feb/2010) and i was wondering if someone had successfully used it since then ?

Thanks for your help
Stylianos
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Old   March 23, 2010, 09:44
Default Pressure step exactly at the last nodes before the outlet
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Old   March 23, 2010, 10:38
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Kevin Smith
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Your BCs on pressure are not well defined; try using total pressure on the outlet.
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Old   March 23, 2010, 13:28
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Stylianos Kyriacou
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If the outlet is part of the rotating portion of the mesh dose that create a problem for MRFSimpleFoam?
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