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Plotting coordinates of face centroids

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Old   May 7, 2009, 07:19
Default Plotting coordinates of face centroids
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Hi @all,

I'm trying to display the coordinates of the face centroids of a wall zone via UDM in contur plot panel. I'm using the following UDF to determine the coordinates and to put them into UDMs:

#include "udf.h"

DEFINE_ON_DEMAND(face_centrs)
{
Domain *d;
Thread *t;
face_t f;
real x[ND_ND];

int domain_id, blade_id;

domain_id = 1;
blade_id = 17;

/* get the domain pointer to the flow_domain */
d = Get_Domain(domain_id);

/* get the thread pointer to the bladethread */
t = Lookup_Thread(d,blade_id);

begin_f_loop(f,t)
{
F_CENTROID(x,f,t);
F_UDMI(f,t,0)=x[0];
F_UDMI(f,t,1)=x[1];
F_UDMI(f,t,2)=x[2];

Message("y-coord: %f \n", F_UDMI(f,t,1));

}
end_f_loop(f,t);

}

As you can see, I print the y-coordinate to the screen which works perfectly. But when I want to display the UDMs in the contour plot panel, all the values are zero. Can anyone tell where my mistake is?

I'd really appreciate any help.

cheers
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Old   May 7, 2009, 08:21
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Daniel Tanner
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This is a bit painful. Basically the contour plot in fluent only displays cell-centered data, i.e., it interpolates the cell-centre value to the face and then displays it. If you are using F_UDMI you are not storing the values at the cell centre - hence, it will be zero!

You could use C_UDMI instead but I am not sure if the value you save needs to be adjusted to account for the interpolation. See this link for details on using the C_UDMI for displaying face variables:

How to find the cells adjacent to the wall?
UDF to Access Wall Normal Concentration Gradient
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Old   May 7, 2009, 08:47
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Hey Daniel,

that was exactly the hint I needed, thanks a lot!!!!!

cheers
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