# MRF solvers give diffenrent results when MRF zone's diameter is different

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May 14, 2013, 03:25
MRF solvers give diffenrent results when MRF zone's diameter is different
#1
Senior Member

Dongyue Li
Join Date: Jun 2012
Location: Torino, Italy
Posts: 742
Rep Power: 9
Hi,

Nowdays I intend to make a test of my mrf case's result with the paper.But I find the result vary with the different diameter of my rotating size.I made a comparision in two situation in which only the MRF zones size is different.As you can see in the image.(its a slice of a 3D case)

The first one's MRF zone is smaller than the other.expect this everything is the same.But after 2000 iterations,the velocity is a little different.I dont know if it gets convergence but in 2500s iterations,the velocity looks dont change anymore.

in this thread linnemann happend to run into this situation. but I didnot try his case.http://www.openfoam.org/mantisbt/view.php?id=409

Code:
```Time = 2093

smoothSolver:  Solving for Ux, Initial residual = 0.000157922, Final residual = 1.01677e-05, No Iterations 2
smoothSolver:  Solving for Uy, Initial residual = 0.000172252, Final residual = 9.70874e-06, No Iterations 2
smoothSolver:  Solving for Uz, Initial residual = 0.000168408, Final residual = 1.10209e-05, No Iterations 2
GAMG:  Solving for p, Initial residual = 0.00286416, Final residual = 6.07327e-05, No Iterations 3
time step continuity errors : sum local = 0.000134333, global = -1.86372e-05, cumulative = 0.176384
smoothSolver:  Solving for epsilon, Initial residual = 5.02636e-05, Final residual = 1.76898e-06, No Iterations 2
smoothSolver:  Solving for k, Initial residual = 0.000214597, Final residual = 1.16413e-05, No Iterations 2
ExecutionTime = 3003.18 s  ClockTime = 3019 s```
Code:
```MRF1
{
type            MRFSource;
active          true;
selectionMode   cellZone;
cellZone        innerCylinder;

MRFSourceCoeffs
{
nonRotatingPatches ();
origin      (0 0 0);
axis        (0 1 0);
omega       31.4159;
}
}```
Attached Images
 paper's mesh.jpg (93.1 KB, 41 views) 11.jpg (94.0 KB, 47 views)

 February 18, 2014, 05:30 Are there some news? #2 New Member   Join Date: Feb 2010 Posts: 7 Rep Power: 8 Hi, I found a similar result issue in a different geometry MRF problem. Are there some news? Dothan

 March 10, 2014, 12:22 #3 Member   Pengchuan Wang Join Date: Nov 2012 Location: Michigan USA Posts: 56 Rep Power: 5 Hi everyone, Same thing happens to me as well. Different size of MRFzones gives different results. And for me, none of these gives me the same results as the analytical solution.

 March 11, 2014, 03:44 #4 New Member   Join Date: Feb 2010 Posts: 7 Rep Power: 8 Hi pechwang, Do you have a turbomachinery analytical solution to compare CFD solutiuons? I know only Eckardt Impeller. Dothan

 March 11, 2014, 11:06 #5 Member   Pengchuan Wang Join Date: Nov 2012 Location: Michigan USA Posts: 56 Rep Power: 5 Hi Dothan, No, the analytical solution is for lubrication model. Unfortunately, MRF cannot give me correct results. Thanks, Pengchuan

 May 29, 2015, 07:00 #6 Senior Member   M. Montero Join Date: Mar 2009 Location: Madrid Posts: 121 Rep Power: 9 Same problem here. When MRFZone limit is near walls ( sometimes it is required because stator zone is quite near) the pressure field around the walls is modified. The pressure lines are modified to accommodate its shape to the limit of the MRF Zone so suction lobe is affected and so all the aerodynamics of the wall (wake,....). The solution is wrong. I do not have AMI interfaces so the solution proposed does not work. Did you start a bug report?

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