Nigirim 
November 13, 2012 05:13 
Calculation of k and epsilon freezes
Hi all,
I've got a problem with my calculation von k and epsilon.
I'm trying to simulate a rotating geometry with a modified version of interFoam. The geometry is rotating in different directions and my fluid is
sloshing, but the values for k and epsilon just dont chance anymore after some iterations.
At the beginning there are some Iterations for k and epsilon
Code:
MULES: Solving for alpha1
Liquid phase volume fraction = 0.979575 Min(alpha1) = 2.49977e20 Max(alpha1) = 1
MULES: Solving for alpha1
Liquid phase volume fraction = 0.979575 Min(alpha1) = 7.02031e21 Max(alpha1) = 1
MULES: Solving for alpha1
Liquid phase volume fraction = 0.979575 Min(alpha1) = 1.31893e20 Max(alpha1) = 1
MULES: Solving for alpha1
Liquid phase volume fraction = 0.979575 Min(alpha1) = 4.39865e20 Max(alpha1) = 1
DICPCG: Solving for p_rgh, Initial residual = 0.00109002, Final residual = 8.85396e08, No Iterations 124
time step continuity errors : sum local = 1.83749e09, global = 2.10194e11, cumulative = 6.24155e11
DICPCG: Solving for p_rgh, Initial residual = 0.000154468, Final residual = 9.29858e08, No Iterations 114
time step continuity errors : sum local = 1.93264e09, global = 1.87438e10, cumulative = 2.49854e10
DICPCG: Solving for p_rgh, Initial residual = 2.61918e05, Final residual = 9.23886e08, No Iterations 79
time step continuity errors : sum local = 1.9189e09, global = 2.37918e10, cumulative = 1.19357e11
DILUPBiCG: Solving for epsilon, Initial residual = 0.000340262, Final residual = 6.24431e09, No Iterations 2
bounding epsilon, min: 4.02028e08 max: 0.107857 average: 5.80718e05
DILUPBiCG: Solving for k, Initial residual = 0.000539149, Final residual = 1.33527e11, No Iterations 4
bounding k, min: 7.24082e12 max: 0.00100971 average: 1.00796e05
ExecutionTime = 17.68 s ClockTime = 18 s
but later on, at about 0.2s (first directionchange is at 0.5s) it pretty much looks like this:
Code:
MULES: Solving for alpha1
Liquid phase volume fraction = 0.979575 Min(alpha1) = 2.15831e20 Max(alpha1) = 1.00001
MULES: Solving for alpha1
Liquid phase volume fraction = 0.979575 Min(alpha1) = 2.96242e20 Max(alpha1) = 1.00001
MULES: Solving for alpha1
Liquid phase volume fraction = 0.979575 Min(alpha1) = 1.20443e20 Max(alpha1) = 1.00001
MULES: Solving for alpha1
Liquid phase volume fraction = 0.979575 Min(alpha1) = 9.61596e21 Max(alpha1) = 1.00001
DICPCG: Solving for p_rgh, Initial residual = 0.000269819, Final residual = 9.59801e08, No Iterations 26
time step continuity errors : sum local = 1.39057e09, global = 1.24122e10, cumulative = 4.05415e08
DICPCG: Solving for p_rgh, Initial residual = 1.5512e05, Final residual = 9.55703e08, No Iterations 21
time step continuity errors : sum local = 1.3846e09, global = 1.14579e10, cumulative = 4.04269e08
DICPCG: Solving for p_rgh, Initial residual = 1.98201e06, Final residual = 9.75346e08, No Iterations 5
time step continuity errors : sum local = 1.41305e09, global = 1.08762e10, cumulative = 4.03181e08
DILUPBiCG: Solving for epsilon, Initial residual = 0.00010125, Final residual = 7.4232e09, No Iterations 1
bounding epsilon, min: 1.98379e18 max: 16.2816 average: 0.00581568
DILUPBiCG: Solving for k, Initial residual = 9.96483e11, Final residual = 9.96483e11, No Iterations 0
ExecutionTime = 936.41 s ClockTime = 977 s
Right now I'm using realizableKE as turbulence model, but I also tried to run it wie kOmegaSST with the same result.
I tried several things I found on the internet including:  Changing mesh quality (changed it between 20.000 and 100.000 cells)
 Decreasing and increasing the timesteps
 Changing my BCs for k, epsilon and nut
 Used other schemes
 Added some extra layers to my mesh
 Changing the tolerance for k and epsilon
 Changing my relaxation factors
But still my simulation looks pretty much the same, just the change of my tolerance resulted in an increase of the time that k and epsilon are calculated but still only about 1s out of 2s.
Here are my current BCs for k, epsilon and nut
k
Code:
boundaryField
{
outlet
{
type inletOutlet;
inletValue uniform 0.001;
value uniform 0.01;
}
symmetry
{
type symmetryPlane;
}
wall
{
type kqRWallFunction;
value uniform 1e06;
}
epsilon
Code:
boundaryField
{
outlet
{
type inletOutlet;
inletValue uniform 0.0001;
value uniform 0;
}
symmetry
{
type symmetryPlane;
}
wall
{
type epsilonWallFunction;
value uniform 0.001;
}
nut
Code:
boundaryField
{
outlet
{
type calculated;
value uniform 0;
}
symmetry
{
type symmetryPlane;
}
wall
{
type nutkWallFunction;
value uniform 0;
}
I still think there is something with my BCs, but I dont know whats wrong or
causing the problem.
If anyone has an idea what I could do, please let me know.
My englisch isnt the best so if you dont understand something just ask me :D
Greets
Nigirim
