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-   -   continuity error with simpleFOAM in duct flow (https://www.cfd-online.com/Forums/openfoam-solving/72598-continuity-error-simplefoam-duct-flow.html)

lbordier February 11, 2010 09:56

continuity error with simpleFOAM in duct flow
 
Hello,

I'm trying to set up a case for duct flow with simpleFOAM.
I know the inlet & outlet pressure, so I tried to fix BC in consequence but i guess i've mistaken somewhere because I've very high continuity errors.

Thank you for any comment / advice.

The setting of the bc and some logs are given below :

for velocity :
dimensions [0 1 -1 0 0 0 0];

internalField uniform (0 0 0);

boundaryField
{
Inlet
{
type pressureInletVelocity;
value uniform (0 0 0);
}

Outlet
{
type zeroGradient;
//value uniform (0 0 0);
}

Wall
{
type fixedValue;
value uniform (0 0 0);
}
}


for pressure :

dimensions [0 2 -2 0 0 0 0];

internalField uniform 0;

boundaryField
{
Inlet
{
type fixedValue;
value uniform 0;
}

Outlet
{
type fixedValue;
value uniform -1659.751;
}

Wall
{
type zeroGradient;
}
}


some log for laminar run :

Time = 268

DILUPBiCG: Solving for Ux, Initial residual = 0.0250111, Final residual = 1.79843e-06, No Iterations 3
DILUPBiCG: Solving for Uy, Initial residual = 0.0247072, Final residual = 1.19593e-06, No Iterations 3
DILUPBiCG: Solving for Uz, Initial residual = 0.0285379, Final residual = 1.2351e-06, No Iterations 3
GAMG: Solving for p, Initial residual = 0.0515492, Final residual = 0.000424851, No Iterations 5
GAMG: Solving for p, Initial residual = 0.0101859, Final residual = 9.71891e-05, No Iterations 3
time step continuity errors : sum local = 259841, global = -10979.7, cumulative = -206963
ExecutionTime = 7931.91 s ClockTime = 7933 s

Time = 269

DILUPBiCG: Solving for Ux, Initial residual = 0.0250091, Final residual = 1.86461e-06, No Iterations 3
DILUPBiCG: Solving for Uy, Initial residual = 0.0247248, Final residual = 1.15719e-06, No Iterations 3
DILUPBiCG: Solving for Uz, Initial residual = 0.0285198, Final residual = 1.22932e-06, No Iterations 3
GAMG: Solving for p, Initial residual = 0.0516174, Final residual = 0.000425292, No Iterations 5
GAMG: Solving for p, Initial residual = 0.0101802, Final residual = 9.74468e-05, No Iterations 3
time step continuity errors : sum local = 272986, global = -11533.7, cumulative = -218496
ExecutionTime = 7962.34 s ClockTime = 7964 s

Mesh check :

Checking geometry...
Domain bounding box: (0.478596 0.0186977 0.111428) (0.683153 0.121314 0.475742)
Boundary openness (-3.99958e-20 -1.02563e-19 -8.1168e-20) OK.
Max cell openness = 2.13144e-16 OK.
Max aspect ratio = 6.79448 OK.
Minumum face area = 1.45022e-09. Maximum face area = 6.95171e-06. Face area magnitudes OK.
Min volume = 2.10867e-13. Max volume = 2.42119e-08. Total volume = 0.00117081. Cell volumes OK.
Mesh non-orthogonality Max: 71.8538 average: 13.8243
*Number of severely non-orthogonal faces: 1.
Non-orthogonality check OK.
<<Writing 1 non-orthogonal faces to set nonOrthoFaces
Face pyramids OK.
Max skewness = 2.20433 OK.
*There are 250 faces with concave angles between consecutive edges. Max concave angle = 89.457 degrees.
<<Writing 250 faces with concave angles to set concaveFaces
Face flatness (1 = flat, 0 = butterfly) : average = 0.990544 min = 0.755141
*There are 47 faces with ratio between projected and actual area < 0.8
Minimum ratio (minimum flatness, maximum warpage) = 0.755141
<<Writing 47 warped faces to set warpedFaces

Mesh OK.

santos February 12, 2010 06:10

Hi,

Please change the pressure inlet boundary condition to zeroGradient.

Regards,
Jose Santos

lbordier February 15, 2010 06:20

It seems that it converge better with the following settings for p :

boundaryField
{
Inlet
{
//type zeroGradient;
type fixedValue;
value uniform 0.0;
}

Outlet
{
//type zeroGradient;
type timeVaryingUniformFixedValue;
fileName "pressure_ramp.dat";
outOfBounds clamp;
//value uniform -2000.0;
}

Wall
{
type zeroGradient;
}
}

adding a pressure ramp makes the continuity errors to be reduced


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