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-   -   cylindrical coordinate vs cartesian coordinate (http://www.cfd-online.com/Forums/fluent/32622-cylindrical-coordinate-vs-cartesian-coordinate.html)

Lam November 29, 2003 17:28

cylindrical coordinate vs cartesian coordinate
 
I face a problem in comparing my CFD results (Fluent) with my LDA measures(Dantec) because they use cylindrical coordinate and cartesian coordinate respectively. Can I change the Fluent from a cylindrical coordinate to a cartesian coordinate?

thomas December 1, 2003 04:52

Re: cylindrical coordinate vs cartesian coordinate
 
Hi, I dunno if it is what you are looking for but here is the linked between the cartesian and cylindrical coord. in fluent Z -> X r -> Y theta -> Z

You can certainly find more informations on the fluent user web site (online documentation). Cheers, thomas

grayeagle May 1, 2013 18:33

Hi, I'm solving a natural convection problem in Fluent 13, but I want to model a 3D symetric cylindrical shape in 2-d. I assume (r=x, z=y, theta=0).

How can I change my coordinate from Cartesian to cylindrical???

er.mkumar May 10, 2013 04:56

Quote:

Originally Posted by grayeagle (Post 424514)
Hi, I'm solving a natural convection problem in Fluent 13, but I want to model a 3D symetric cylindrical shape in 2-d. I assume (r=x, z=y, theta=0).

How can I change my coordinate from Cartesian to cylindrical???

Go to define/solver...
change your problem from 2D to aisymmetric. That's it.

Best Wishes,
Mukesh

grayeagle May 10, 2013 09:24

cylinderical coordinate in Fluent
 
I have done it. Draw my half shape, and define the symmetry axis as "axis" in Boundary condition, and select 'Axisymmetry' in define-solver, but there is an error : "Divergence detected in AMG solver: x-momentum"

er.mkumar May 10, 2013 13:01

Quote:

Originally Posted by grayeagle (Post 426526)
I have done it. Draw my half shape, and define the symmetry axis as "axis" in Boundary condition, and select 'Axisymmetry' in define-solver, but there is an error : "Divergence detected in AMG solver: x-momentum"

for STEADY PROBLEM: you can try reducing relaxation factor of momentum equation from 0.7 to some lower value i.e, 0.4, 0.5, 0.6 [solve/controls...]

for UNSTAEDY PROBLEM: reduce the size of time step

grayeagle May 10, 2013 18:49

I have reduced relaxation factor of momentum equation from 0.7 to 0.3, 0.4, 0.5, 0.6, ... but there is still that error.
I even close the momentum equation (Solution control-equation) but this time the error was " Divergence detected in AMG solver: temperature " !

er.mkumar May 10, 2013 21:22

Quote:

Originally Posted by grayeagle (Post 426615)
I have reduced relaxation factor of momentum equation from 0.7 to 0.3, 0.4, 0.5, 0.6, ... but there is still that error.
I even close the momentum equation (Solution control-equation) but this time the error was " Divergence detected in AMG solver: temperature " !

Try reducing RF for energy term from 1 to 0.7,0.8.
Else there is some problem with BC.
BTW what is problem you are trying to solve.

oj.bulmer May 11, 2013 09:53

Can you post BCs please?

OJ

grayeagle May 11, 2013 12:39

I have a rectangle ( a cross section of cylinder) I wanna solve Natural convection (and then solidification) problem.
I have a temperature gradient in right and left wall (my rectangle is 40x100). and this UDF is my boundary condition in left and right wall...
I solve it in cartesian coordinate, but in Cylindrical, I have problem.
#include "udf.h"

DEFINE_PROFILE(temperature_profile, thread, index)
{
real x[ND_ND]; /* this will hold the position vector */
real y;
face_t f;

begin_f_loop(f,thread)
{
F_CENTROID(x,f,thread);
y = x[1];
F_PROFILE(f, thread, index) =((1000*y)/2)+1223;
}
end_f_loop(f,thread)
}

grayeagle May 11, 2013 13:05

I solved this problem in Planer (2d space) without any problem.
I reduce the Under-relaxation factor for energy and momentum.
I aslo try to solve it Transient.
But there is still this error.
for momentum equation: " Divergence detected in AMG solver: x-momentum "
for ener


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