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- - **continuity error with simpleFOAM in duct flow**
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continuity error with simpleFOAM in duct flowHello,
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. |

Hi,
Please change the pressure inlet boundary condition to zeroGradient. Regards, Jose Santos |

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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