[ysh1227]

Hi, everyone.

I am new in OF(OF 2.1.0).
I try to run the Small Horizontal Axis Wind Turbine case using MRFSimpleFoam.

First, I simulated that case with the condition that is no rotation and no velocity, and the result is good and there is no problem. The continuity error is very very small that I expected.

However, the problem occured when I simulated that case with no rotation and 7m/s inlet-velocity. After about 30 iterations, the continuity error started to increase more than 1 and finally it became very very big. The results also was very wrong when I view the velocity and pressure fields using paraView due to bad continuity error.
I already tried to change the fvScheme and fvSolver and simulated a lot of cases with the same mesh file. but Always I failed to solve because of the same reason, 'time step continuity error'.

Before simulating this case, I had the AMI problems and resolved it by making a new mesh. So, there is no AMI problems in this case, I already checked it. And my final goal is to use pimpleDyMFoam as soon as possible.

Therefore, I need your help.
Now, I'm typing it with remote control to my computer in lab. so I couldn't show you the detail of my case. But I try to give you the details as mush as possible.

I want you to reply about
1. how I can reduce the continuity error
2. Whether the fvSchemes and fvSolution is proper or not
and 3. better ideas to solve this case.

[more informations about the best but failed case that I've solved]
the log file and files in '0' folder is attached.
http://www.cfd-online.com/Forums/ope...-diverges.html

1. output from the terminal near the problem

PHP Code:

Time = 12
smoothSolver: Solving for Ux, Initial residual = 0.24178, Final residual = 4.66485e-09, No Iterations 24
smoothSolver: Solving for Uy, Initial residual = 0.236673, Final residual = 8.17346e-09, No Iterations 22
smoothSolver: Solving for Uz, Initial residual = 0.232616, Final residual = 5.05721e-09, No Iterations 24
GAMG: Solving for p, Initial residual = 0.00439615, Final residual = 4.39105e-06, No Iterations 936
GAMG: Solving for p, Initial residual = 8.99011e-06, Final residual = 9.74321e-07, No Iterations 10
GAMG: Solving for p, Initial residual = 2.92193e-06, Final residual = 9.18676e-07, No Iterations 3
time step continuity errors : sum local = 1.34624, global = 0.000523313, cumulative = 0.000717847
smoothSolver: Solving for omega, Initial residual = 0.330051, Final residual = 4.44257e-07, No Iterations 8
smoothSolver: Solving for k, Initial residual = 0.0234427, Final residual = 2.08236e-07, No Iterations 10
ExecutionTime = 11239.2 s ClockTime = 11277 s
Time = 13
smoothSolver: Solving for Ux, Initial residual = 0.394172, Final residual = 9.36361e-09, No Iterations 24
smoothSolver: Solving for Uy, Initial residual = 0.236768, Final residual = 2.40871e-09, No Iterations 24
smoothSolver: Solving for Uz, Initial residual = 0.355896, Final residual = 9.66341e-09, No Iterations 24
GAMG: Solving for p, Initial residual = 0.00107708, Final residual = 2.64334e-06, No Iterations 1000
GAMG: Solving for p, Initial residual = 3.54345e-05, Final residual = 1.29183e-06, No Iterations 1000
GAMG: Solving for p, Initial residual = 9.14944e-06, Final residual = 9.99899e-07, No Iterations 39
time step continuity errors : sum local = 0.686033, global = 0.000218238, cumulative = 0.000936085
smoothSolver: Solving for omega, Initial residual = 0.425149, Final residual = 3.32176e-07, No Iterations 12
smoothSolver: Solving for k, Initial residual = 0.0224997, Final residual = 4.76061e-07, No Iterations 8
ExecutionTime = 12351.3 s ClockTime = 12392 s
Time = 14
smoothSolver: Solving for Ux, Initial residual = 0.195003, Final residual = 2.3199e-09, No Iterations 24
smoothSolver: Solving for Uy, Initial residual = 0.173547, Final residual = 9.25896e-09, No Iterations 22
smoothSolver: Solving for Uz, Initial residual = 0.19108, Final residual = 2.86689e-09, No Iterations 24
GAMG: Solving for p, Initial residual = 0.00154395, Final residual = 1.54298e-06, No Iterations 907
GAMG: Solving for p, Initial residual = 3.66792e-06, Final residual = 8.65631e-07, No Iterations 2
GAMG: Solving for p, Initial residual = 1.34099e-06, Final residual = 7.70434e-07, No Iterations 1
time step continuity errors : sum local = 4.70061, global = -0.00500594, cumulative = -0.00406985
smoothSolver: Solving for omega, Initial residual = 0.333175, Final residual = 5.88616e-07, No Iterations 6
smoothSolver: Solving for k, Initial residual = 0.0389014, Final residual = 2.82821e-07, No Iterations 8
ExecutionTime = 12859 s ClockTime = 12902 s
Time = 15
smoothSolver: Solving for Ux, Initial residual = 0.178065, Final residual = 6.43032e-09, No Iterations 22
smoothSolver: Solving for Uy, Initial residual = 0.214259, Final residual = 2.16551e-09, No Iterations 24
smoothSolver: Solving for Uz, Initial residual = 0.196981, Final residual = 7.3701e-09, No Iterations 22
GAMG: Solving for p, Initial residual = 0.000258065, Final residual = 9.99113e-07, No Iterations 917
GAMG: Solving for p, Initial residual = 3.00182e-07, Final residual = 3.00182e-07, No Iterations 0
GAMG: Solving for p, Initial residual = 3.00182e-07, Final residual = 3.00182e-07, No Iterations 0
time step continuity errors : sum local = 53.2202, global = -0.00137399, cumulative = -0.00544385
smoothSolver: Solving for omega, Initial residual = 0.333346, Final residual = 3.29517e-07, No Iterations 8
smoothSolver: Solving for k, Initial residual = 0.217336, Final residual = 2.4148e-07, No Iterations 12
ExecutionTime = 13368.8 s ClockTime = 13413 s
Time = 16
smoothSolver: Solving for Ux, Initial residual = 0.33311, Final residual = 2.71606e-09, No Iterations 22
smoothSolver: Solving for Uy, Initial residual = 0.278035, Final residual = 9.89641e-09, No Iterations 22
smoothSolver: Solving for Uz, Initial residual = 0.299317, Final residual = 3.8482e-09, No Iterations 22
GAMG: Solving for p, Initial residual = 7.77667e-06, Final residual = 9.36191e-07, No Iterations 6
GAMG: Solving for p, Initial residual = 1.15861e-06, Final residual = 9.26386e-07, No Iterations 1
GAMG: Solving for p, Initial residual = 8.8794e-07, Final residual = 8.8794e-07, No Iterations 0
time step continuity errors : sum local = 138.064, global = -0.143375, cumulative = -0.148819
smoothSolver: Solving for omega, Initial residual = 0.333087, Final residual = 1.17684e-07, No Iterations 6
smoothSolver: Solving for k, Initial residual = 0.0501571, Final residual = 3.91316e-07, No Iterations 12
ExecutionTime = 13391.3 s ClockTime = 13436 s
Time = 17
smoothSolver: Solving for Ux, Initial residual = 0.167577, Final residual = 2.71625e-09, No Iterations 24
smoothSolver: Solving for Uy, Initial residual = 0.132945, Final residual = 3.52546e-09, No Iterations 22
smoothSolver: Solving for Uz, Initial residual = 0.154564, Final residual = 2.4897e-09, No Iterations 24
GAMG: Solving for p, Initial residual = 1.56889e-05, Final residual = 8.79822e-07, No Iterations 2
GAMG: Solving for p, Initial residual = 6.76478e-09, Final residual = 6.76478e-09, No Iterations 0
GAMG: Solving for p, Initial residual = 6.76478e-09, Final residual = 6.76478e-09, No Iterations 0
time step continuity errors : sum local = 427.601, global = -0.153837, cumulative = -0.302656
smoothSolver: Solving for omega, Initial residual = 0.333002, Final residual = 6.87238e-07, No Iterations 10
smoothSolver: Solving for k, Initial residual = 0.432678, Final residual = 3.14185e-07, No Iterations 10
ExecutionTime = 13411.8 s ClockTime = 13456 s 


2) structure of my case
I attached the file.


3) boundary

PHP Code:

BLADEFIRST
{
type wall;
nFaces 28088;
startFace 32433504;
}
BLADESECOND
{
type wall;
nFaces 28088;
startFace 32461592;
}
HUB
{
type wall;
nFaces 8924;
startFace 32489680;
}
AMI_DISK_FRONT
{
type cyclicAMI;
nFaces 64812;
startFace 32498604;
matchTolerance 0.001;
neighbourPatch AMI_DOMAIN_FRONT;
transform noOrdering;
}
AMI_DISK_BACK
{
type cyclicAMI;
nFaces 64812;
startFace 32563416;
matchTolerance 0.001;
neighbourPatch AMI_DOMAIN_BACK;
transform noOrdering;
}
AMI_DISK_SIDE
{
type cyclicAMI;
nFaces 40468;
startFace 32628228;
matchTolerance 0.001;
neighbourPatch AMI_DOMAIN_SIDE;
transform noOrdering;
}
AMI_DOMAIN_FRONT
{
type cyclicAMI;
nFaces 29440;
startFace 32668696;
matchTolerance 0.001;
neighbourPatch AMI_DISK_FRONT;
transform noOrdering;
}
AMI_DOMAIN_BACK
{
type cyclicAMI;
nFaces 19968;
startFace 32698136;
matchTolerance 0.001;
neighbourPatch AMI_DISK_BACK;
transform noOrdering;
}
AMI_DOMAIN_SIDE
{
type cyclicAMI;
nFaces 11776;
startFace 32718104;
matchTolerance 0.001;
neighbourPatch AMI_DISK_SIDE;
transform noOrdering;
}
INLET_VELOCITY
{
type patch;
nFaces 38656;
startFace 32729880;
}
OUTLE_PRESSURE
{
type patch;
nFaces 29184;
startFace 32768536;
}
SYMMETRY
{
type wall;
nFaces 41984;
startFace 32797720;
} 


4) MRFZones

PHP Code:

FLUID
{
// Fixed patches (by default they 'move' with the MRF zone)
nonRotatingPatches (AMI_DISK_FRONT AMI_DISK_BACK AMI_DISK_SIDE AMI_DOMAIN_FRONT AMI_DOMAIN_BACK AMI_DOMAIN_SIDE);
origin origin [0 1 0 0 0 0 0] (0 0 0);
axis axis [0 0 0 0 0 0 0] (0 0 1);
omega omega [0 0 -1 0 0 0 0] 0;
} 


5) fvSchemes

PHP Code:

ddtSchemes
{
default steadyState;
}
gradSchemes
{
default Gauss linear;
grad(p) Gauss linear;
grad(U) Gauss linear;
}
divSchemes
{
// default none;
// div(phi,U) Gauss limitedLinearV 1;
// div(phi,k) Gauss limitedLinear 1;
// div(phi,omega) Gauss limitedLinear 1;
// div((nuEff*dev(T(grad(U))))) Gauss linear;
default none;
div(phi,U) Gauss upwind;
div(phi,U) Gauss linearUpwind grad(U);
div(phi,k) Gauss upwind;
div(phi,omega) Gauss upwind;
div((nuEff*dev(T(grad(U))))) Gauss linear;
}
laplacianSchemes
{
default Gauss linear corrected;
}
interpolationSchemes
{
default linear;
interpolate(U) linear;
}
snGradSchemes
{
default corrected;
}
fluxRequired
{
default no;
p ;
} 


6) fvSolution

PHP Code:

solvers
{
p
{
solver GAMG;
tolerance 1e-06;
relTol 0.001;
smoother GaussSeidel;
cacheAgglomeration true;
nCellsInCoarsestLevel 20;
agglomerator faceAreaPair;
mergeLevels 1;
}
U
{
solver smoothSolver;
smoother GaussSeidel;
nSweeps 2;
tolerance 1e-08;
relTol 0;
}
k
{
solver smoothSolver;
smoother GaussSeidel;
nSweeps 2;
tolerance 1e-06;
relTol 0;
}
omega
{
solver smoothSolver;
smoother GaussSeidel;
nSweeps 2;
tolerance 1e-06;
relTol 0;
}
}
SIMPLE
{
nNonOrthogonalCorrectors 2;
pRefCell 0;
pRefValue 0;
}
relaxationFactors
{
fields
{
p 0.3;
}
equations
{
U 0.5;
k 0.5;
omega 0.5;
}
} 


[davidtran]

Hi,

Did you handle your problem? I would like to know your solution about this issue. Now, I am dealing with small wind turbine using MRF+simpleFoam and AMI interface? However, I faced the similar issue as you did.
I looking forward to hearing from you.
Best regards,