Instability introduced by using mutRoughWallFunctions?

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March 10, 2014, 13:26
Instability introduced by using mutRoughWallFunctions?
#1
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Alex Chan
Join Date: Jan 2014
Location: Amherst, MA
Posts: 10
Rep Power: 12
All,

I am trying to implement the use of rough wall functions in a nozzle case. Roughness seems to make the cases crash for no reason. Any experience determining Ks and Cs values?

Some info:

Diameter: 200 microns
Inlet Pressure: 15 MPa
Outlet Pressure: 220 kPa
Axisymmetric, 5 degree wedge
Solver: custom multiphase flow solver
Ks: 1e-6
Cs: 0.5

-There are no signs of anything bad from the residuals (pyFoamPlotWatcher image attached).

-Here's the last iteration from my outfile where it abruptly stops with a floating point exception.

Quote:
 Minimum pressure is 7.26454 [MPa] Maximum pressure is 15.0082 [MPa] Minimum density is 36.5875 [kg/m3] Maximum density is 718.337 [kg/m3] Maximum velocity is 133.745 [m/s] Mass flux at centerline = 0 Momentum flux at centerline = 0 Mass flux at frontAndBackPlanes = 0 Momentum flux at frontAndBackPlanes = 0 Mass flux at frontAndBackPlanes_neg = -3.33872e-10 Momentum flux at frontAndBackPlanes_neg = -8.53365e-08 Mass flux at frontAndBackPlanes_pos = -3.33872e-10 Momentum flux at frontAndBackPlanes_pos = -8.53365e-08 Mass flux at inlet = -2.0674e-05 Momentum flux at inlet = -9.16769e-05 Mass flux at outlet = 1.70816e-05 Momentum flux at outlet = 6.56206e-05 Mass flux at wall = 0 Momentum flux at wall = 0 Time = 2.14247e-05 Net mass flux = -3.59313e-06 Mass flux through nozzle Tracer1 at boundary centerline = 0 total tracer value 0 Mass flux through nozzle Tracer1 at boundary frontAndBackPlanes = 0 total tracer value 0 Mass flux through nozzle Tracer1 at boundary frontAndBackPlanes_neg = 1.38041e-09 total tracer value 6530.31 Mass flux through nozzle Tracer1 at boundary frontAndBackPlanes_pos = 1.38041e-09 total tracer value 6530.31 Mass flux through nozzle Tracer1 at boundary inlet = -2.0674e-05 total tracer value 29 Mass flux through nozzle Tracer1 at boundary outlet = 8.60793e-73 total tracer value 1.64044e-66 Mass flux through nozzle Tracer1 at boundary wall = 0 total tracer value 109.401 Courant Number mean: 0.00340225 max: 0.500047 velocity magnitude: 130.963 deltaT = 2.65879e-09 Time = 2.14274e-05 DILUPBiCG: Solving for rho, Initial residual = 1.25259e-05, Final residual = 2.67179e-10, No Iterations 1 volume continuity errors : volume = 1.73046e-11, max error = 0, sum local = 0, global = 0 DILUPBiCG: Solving for x: solution singularity DILUPBiCG: Solving for y, Initial residual = 1.88362e-05, Final residual = 5.72639e-10, No Iterations 1 DILUPBiCG: Solving for Tracer1, Initial residual = 1.88365e-05, Final residual = 4.22274e-10, No Iterations 1 DILUPBiCG: Solving for epsilon, Initial residual = 1.75258e-05, Final residual = 7.51016e-09, No Iterations 2 DILUPBiCG: Solving for k, Initial residual = 3.66563e-05, Final residual = 2.34053e-08, No Iterations 2
-After solving for k, it solves for Ux.

Any and all advice appreciated!
Attached Images
 5MicronV4Rough1e-6.png (10.2 KB, 2 views)

March 18, 2014, 14:14
#2
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Alex Chan
Join Date: Jan 2014
Location: Amherst, MA
Posts: 10
Rep Power: 12
Further progress: Here's the crash after compiling foam-extend-3.0 on Debug mode. This is the output of the gdb backtrace:

Quote:
 (gdb) bt #0 0x00007ffff162ead4 in log () from /lib64/libm.so.6 #1 0x00007ffff5bd67ad in Foam::log (s=-0.0072670797110974744) at /home/achan/foam/foam-extend-3.0/src/foam/lnInclude/Scalar.H:242 #2 0x00007ffff3af7d9e in Foam::compressible::RASModel::yPlusLam (this=0xd3bb10, kappa=0.40999999999999998, E=0.95255364484361649) at RASModel/RASModel.C:162 #3 0x00007ffff3bca35a in Foam::compressible::RASModels::mutRoughWallFunctio nFvPatchScalarField::calcMut ( this=0xd41d10) at derivedFvPatchFields/wallFunctions/mutWallFunctions/mutRoughWallFunction/mutRoughWallFunctionFvPatchScalarField.C:98 #4 0x00007ffff3bc9321 in Foam::compressible::RASModels::mutWallFunctionFvPa tchScalarField::updateCoeffs ( this=0xd41d10) at derivedFvPatchFields/wallFunctions/mutWallFunctions/mutWallFunction/mutWallFunctionFvPatchScalarField.C:192 #5 0x00000000004c0ff5 in Foam::fvPatchField::evaluate (this=0xd41d10) at /home/achan/foam/foam-extend-3.0/src/finiteVolume/lnInclude/fvPatchField.C:237 #6 0x00000000004b12d9 in Foam::GeometricField::GeometricBoundaryField::evaluate (this=0xd3c350) at /home/achan/foam/foam-extend-3.0/src/foam/lnInclude/GeometricBoundaryField.C:308 #7 0x000000000049ba1e in Foam::GeometricField::correctBoundaryConditions (this=0xd3c278) at /home/achan/foam/foam-extend-3.0/src/foam/lnInclude/GeometricField.C:880 #8 0x00007ffff3b37e4c in Foam::compressible::RASModels::kEpsilon::correct (this=0xd3bb10) at kEpsilon/kEpsilon.C:335
In the calculation of yPlusLam(), the line with the log is bolded below:

Quote:
 scalar RASModel::yPlusLam(const scalar kappa, const scalar E) const { scalar ypl = 11.0; for (int i=0; i<10; i++) { ypl = log(E*ypl)/kappa; } return ypl; }
So somehow E*ypl is returning negative?

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