Difference in values of velocity contour and velocity vector

dreamz · July 13, 2015, 13:36

I plotted a velocity contour and velocity vectors for a problem whose converged solution was obtained. I noticed that the values of the minimum and maximum values shown are different in both cases. I want to know what could be the possible reason? What is the exact value of minimum and maximum velocity in the domain?

Kindly help

lixuefang · October 13, 2016, 21:50

Have you found the reason? I met the same problem recently.

Zbynek · October 17, 2016, 04:09

If you want to know the maximum and minimum of a quantity in a domain, just go to Report->Volume Integrals and choose Minimum/Maximum of the quantity. That's it.

As for the reason why the scale is different for vectors and contours - I do not know it but I guess that it may have something to do with the way how Fluent computes the auto-scale. This may be different for vectors and contours.

lixuefang · October 17, 2016, 04:43

Thank you, Zbynek. I know how to get the maximum and minimum values. I tried to export all the data on a surface to a ASCII file to see what the values were there, but failed to find out the reported max or min values. I am thinking about the Finite Volume Method that used in Fluent. Hope to find out how to calculate the values on node and facet center. If you have any idea, please let me know. You can get to me here or by email, lixfthu@hotmail.com

Zbynek · October 17, 2016, 08:55

I am not sure I am answering any better now but - to get face values, use UDFs. You can simply use F_U to get x-velocity on a face, if you combine that with begin_f_loop(f,t), you can print the face values in a file and study the outputs.

jotac · February 22, 2017, 06:43

Hi guys, I just found out why. From the Fluent User Manual: "toggles between using scalar field values at nodes and at cell centers for computing the contours. When the Filled option is off, Node Values is always on."

So basically the difference is due to the reference point you take info from. Hope it helps someone in the future

Cheers,
Jota

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October 13, 2016, 21:50		#2
lixuefang New Member Join Date: Oct 2016 Posts: 2 Rep Power: 0	Have you found the reason? I met the same problem recently.

October 17, 2016, 04:09		#3
Zbynek Member Join Date: Jun 2016 Posts: 66 Rep Power: 10	If you want to know the maximum and minimum of a quantity in a domain, just go to Report->Volume Integrals and choose Minimum/Maximum of the quantity. That's it. As for the reason why the scale is different for vectors and contours - I do not know it but I guess that it may have something to do with the way how Fluent computes the auto-scale. This may be different for vectors and contours.

October 17, 2016, 04:43		#4
lixuefang New Member Join Date: Oct 2016 Posts: 2 Rep Power: 0	Thank you, Zbynek. I know how to get the maximum and minimum values. I tried to export all the data on a surface to a ASCII file to see what the values were there, but failed to find out the reported max or min values. I am thinking about the Finite Volume Method that used in Fluent. Hope to find out how to calculate the values on node and facet center. If you have any idea, please let me know. You can get to me here or by email, lixfthu@hotmail.com

October 17, 2016, 08:55		#5
Zbynek Member Join Date: Jun 2016 Posts: 66 Rep Power: 10	I am not sure I am answering any better now but - to get face values, use UDFs. You can simply use F_U to get x-velocity on a face, if you combine that with begin_f_loop(f,t), you can print the face values in a file and study the outputs.

February 22, 2017, 06:43		#6
jotac New Member Jose Carlos Join Date: May 2013 Posts: 6 Rep Power: 12	Hi guys, I just found out why. From the Fluent User Manual: "toggles between using scalar field values at nodes and at cell centers for computing the contours. When the Filled option is off, Node Values is always on." So basically the difference is due to the reference point you take info from. Hope it helps someone in the future Cheers, Jota