fixed value in the domain for a UDS in case of multiphase flow

swati_mohanty · November 30, 2010, 01:11

Dear all,

I need to calculate the UDS once for the domain, which will be fixed. I will be using the gradient of this UDS for subsequent calculations. I have used C_CENTROID(x,c,t) to get the co-ordinates, which I use for calculation of F_PROFILE(f,t,i). I then hook this profile to UDS. However, when I plot the contour of UDS, it does not show what I desire. I try compiling the same code for UDS outside FLUENT and plot the contour, I get the correct result. Could somebody help why the values are different. Does, F_PROFILE store the x and y cordinates for the point for which the calculations are being made.
with thanx

sm

KristianEtienne · November 30, 2010, 01:54

Hi,

My guess is that your problems are because of C_CENTROID finds the coordinates of the cell center, while F_PROFILE refers to the faces on this cell. The coordinates are different for the cell center than for the face center, so if you are using the centroid of the cell to compute the gradient and imposing it at a face, you will not get what you expect.

Compare for instance the face value F_UDSI(f,ft,uds0) to the cell value C_UDSI(c,ct,uds0) and you will see a difference in these also.

Cheers!

swati_mohanty · November 30, 2010, 03:17

Dear Kristian,

Thanx for your reply. But even after making the changes I do not get the desired results. In fact the deviation is very large. That's why I wonder what are the coordinates of the point at which F_PROFILE is being calculated. Kindly refer to Fluent 6.3 UDF Manual, pg 2-74, where they have used C_CENTROID and F_PROFILE.

sm

November 30, 2010, 01:11	fixed value in the domain for a UDS in case of multiphase flow	#1
swati_mohanty New Member sm Join Date: Jun 2009 Posts: 15 Rep Power: 16	Dear all, I need to calculate the UDS once for the domain, which will be fixed. I will be using the gradient of this UDS for subsequent calculations. I have used C_CENTROID(x,c,t) to get the co-ordinates, which I use for calculation of F_PROFILE(f,t,i). I then hook this profile to UDS. However, when I plot the contour of UDS, it does not show what I desire. I try compiling the same code for UDS outside FLUENT and plot the contour, I get the correct result. Could somebody help why the values are different. Does, F_PROFILE store the x and y cordinates for the point for which the calculations are being made. with thanx sm

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November 30, 2010, 01:54		#2
KristianEtienne New Member Kristian Etienne Einarsrud Join Date: Oct 2010 Location: Trondheim Posts: 29 Rep Power: 15	Hi, My guess is that your problems are because of C_CENTROID finds the coordinates of the cell center, while F_PROFILE refers to the faces on this cell. The coordinates are different for the cell center than for the face center, so if you are using the centroid of the cell to compute the gradient and imposing it at a face, you will not get what you expect. Compare for instance the face value F_UDSI(f,ft,uds0) to the cell value C_UDSI(c,ct,uds0) and you will see a difference in these also. Cheers!

November 30, 2010, 03:17		#3
swati_mohanty New Member sm Join Date: Jun 2009 Posts: 15 Rep Power: 16	Dear Kristian, Thanx for your reply. But even after making the changes I do not get the desired results. In fact the deviation is very large. That's why I wonder what are the coordinates of the point at which F_PROFILE is being calculated. Kindly refer to Fluent 6.3 UDF Manual, pg 2-74, where they have used C_CENTROID and F_PROFILE. sm