# BC settings to expand pressure on atmosphere - simpleFoam / totalPressure

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February 8, 2010, 06:22
BC settings to expand pressure on atmosphere - simpleFoam / totalPressure
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Join Date: Nov 2009
Location: Munich
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Hi Foamers,

I have a problem with the definition of boundary conditions.
I'm running a relativly easy case - standard backward facing step - with simpleFoam (kepsilon turbulence model) to compare the OF results with some other calculations.

At the inlet I have a velocity of 6,02 m/s and at the outlet I want the pressure to expand to normal atmospheric pressure (101325 Pa). My problem is, that I don't realy know, how to set the correct conditions for the inlet/outlet.

At the moment I have for U
Quote:
 inlet { type fixedValue; value uniform (6.02 0 0); } outlet { type fixedValue; value uniform (0 0 0); } wall { type fixedValue; value uniform (0 0 0); }
and for p
Quote:
 inlet { type zeroGradient; } outlet {type fixedValue; value uniform 0; } wall { type zeroGradient; }
My boundarys are
Quote:
 inlet { type patch; physicalType inlet; } outlet { type patch; physicalType outlet; }
With these settings, the simulation runs fine, but it's not exactly what I need.

I tried totalPressure with these settings - wall stays the same:
for p
Quote:
 inlet { type totalPressure; p0 uniform 1.01325e+05; U U; phi phi; rho none; psi none; gamma 1.4; } outlet { type totalPressure; p0 uniform 1.01325e+05; U U; phi phi; rho none; psi none; gamma 1.4; }
for U
Quote:
 inlet { type fixedValue; value uniform (6.02 0 0); } outlet { type zeroGradient; }
But then the simulation crashes after a few steps:
Quote:
 Time = 0.4 DILUPBiCG: Solving for Ux, Initial residual = 0.4226, Final residual = 0.0131669, No Iterations 1 DILUPBiCG: Solving for Uy, Initial residual = 0.385886, Final residual = 0.00659647, No Iterations 1 GAMG: Solving for p, Initial residual = 0.993287, Final residual = 0.00404666, No Iterations 1 time step continuity errors : sum local = 14029.9, global = -1.97454, cumulative = -52.1146 DILUPBiCG: Solving for epsilon, Initial residual = 0.245904, Final residual = 0.00112502, No Iterations 1 bounding epsilon, min: -5.08864e+15 max: 2.93019e+16 average: 6.86567e+11 DILUPBiCG: Solving for k, Initial residual = 0.796412, Final residual = 0.0271624, No Iterations 1 bounding k, min: -7.85411e+07 max: 3.01688e+10 average: 2.10361e+06 ExecutionTime = 5.7 s ClockTime = 6 s Time = 0.5 DILUPBiCG: Solving for Ux, Initial residual = 0.00899943, Final residual = 3.74612e-05, No Iterations 1 DILUPBiCG: Solving for Uy, Initial residual = 0.0728675, Final residual = 9.68172e-05, No Iterations 1 GAMG: Solving for p, Initial residual = 0.976204, Final residual = 0.00756845, No Iterations 5 time step continuity errors : sum local = 211598, global = 3456.42, cumulative = 3404.3 DILUPBiCG: Solving for epsilon, Initial residual = 2.35526e-05, Final residual = 3.37908e-07, No Iterations 1 bounding epsilon, min: -1.98511e+19 max: 4.34557e+20 average: 1.11602e+16 DILUPBiCG: Solving for k, Initial residual = 0.000959334, Final residual = 1.61051e-05, No Iterations 1 bounding k, min: -2.44986e+14 max: 9.10124e+14 average: 8.71869e+09 ExecutionTime = 6.37 s ClockTime = 7 s Time = 0.6 DILUPBiCG: Solving for Ux, Initial residual = 0.587131, Final residual = 0.00365698, No Iterations 1 DILUPBiCG: Solving for Uy, Initial residual = 0.381925, Final residual = 0.0271016, No Iterations 1 GAMG: Solving for p, Initial residual = 1, Final residual = 0.0082871, No Iterations 7 time step continuity errors : sum local = 4.51584e+49, global = -1.07389e+49, cumulative = -1.07389e+49 DILUPBiCG: Solving for epsilon, Initial residual = 1, Final residual = 0.00710696, No Iterations 1 bounding epsilon, min: -7.62782e+71 max: 8.5466e+73 average: 1.90599e+69 DILUPBiCG: Solving for k, Initial residual = 1, Final residual = 0.00716964, No Iterations 1 bounding k, min: -6.71536e+58 max: 3.06377e+59 average: 1.93931e+55 ExecutionTime = 7.11 s ClockTime = 8 s Time = 0.7 DILUPBiCG: Solving for Ux, Initial residual = 1, Final residual = 0.00874036, No Iterations 1 DILUPBiCG: Solving for Uy, Initial residual = 1, Final residual = 0.00873079, No Iterations 1 #0 Foam::error:rintStack(Foam::Ostream&) in "/opt/OpenFOAM/OpenFOAM-1.6/lib/linux64GccDPOpt/libOpenFOAM.so" #1 Foam::sigFpe::sigFpeHandler(int) in "/opt/OpenFOAM/OpenFOAM-1.6/lib/linux64GccDPOpt/libOpenFOAM.so" #2 ?? in "/lib/libc.so.6" #3 Foam::PCG::solve(Foam::Field&, Foam::Field const&, unsigned char) const in "/opt/OpenFOAM/OpenFOAM-1.6/lib/linux64GccDPOpt/libOpenFOAM.so" #4 Foam::GAMGSolver::solveCoarsestLevel(Foam::Field&, Foam::Field const&) const in "/opt/OpenFOAM/OpenFOAM-1.6/lib/linux64GccDPOpt/libOpenFOAM.so" #5 Foam::GAMGSolver::Vcycle(Foam::PtrList const&, Foam::Field&, Foam::Field const&, Foam::Field&, Foam::Field&, Foam::Field&, Foam::PtrList >&, Foam::PtrList >&, unsigned char) const in "/opt/OpenFOAM/OpenFOAM-1.6/lib/linux64GccDPOpt/libOpenFOAM.so" #6 Foam::GAMGSolver::solve(Foam::Field&, Foam::Field const&, unsigned char) const in "/opt/OpenFOAM/OpenFOAM-1.6/lib/linux64GccDPOpt/libOpenFOAM.so" #7 Foam::fvMatrix::solve(Foam::dictionary const&) in "/opt/OpenFOAM/OpenFOAM-1.6/lib/linux64GccDPOpt/libfiniteVolume.so" #8 main in "/opt/OpenFOAM/OpenFOAM-1.6/applications/bin/linux64GccDPOpt/simpleFoam" #9 __libc_start_main in "/lib/libc.so.6" #10 _start at /usr/src/packages/BUILD/glibc-2.9/csu/../sysdeps/x86_64/elf/start.S:116
It's clear, that bounding k and epsilon diverge, but I don't understand why. With the first settings, I get fine results.

How do I have to specify the correct BC for the velocity/pressure for my case?
I would realy appreciate your help!

Regards,
Erik

€dit
This is my k-file
Quote:
 inlet { type fixedValue; value uniform 0.0748; } outlet { type zeroGradient; } wall { type kqRWallFunction; value uniform 0.0748; }
This is epsilon
Quote:
 inlet { type fixedValue; value uniform 0.960; } outlet { type zeroGradient; } wall { type epsilonWallFunction; value uniform 0.960; }

 June 15, 2011, 02:49 simpleFoam totalpressure vof #2 Member   hamdi Join Date: Mar 2009 Posts: 75 Rep Power: 10 Hello Foamers, I'm doing a test case on an injector using simplefoam, and I am a bit stuck on the implementation of boundary condition on the pressure (how to use the totalpressure). when I look at the velocity profile they are not the same as in vof. The jet is horizontal in vof, and isn't in simplefoam Can someone help me, it's crucial for my thesis. Thank in advance. Last edited by hamcer; June 20, 2011 at 13:06.

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