# How to calculate pressure forces using custom field functions?

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 June 22, 2009, 07:57 How to calculate pressure forces using custom field functions? #1 New Member   Toni Pujol Join Date: Jun 2009 Posts: 6 Rep Power: 8 Dear all, I am trying to obtain forces and torques on the blades of an axial fan using a transient simulation. I can obtain them by using the Report => Forces panel. However, I would like to obtain them as a function of time. Therefore, I want to create a Custom Field Function and then make a Monitor => Surface of that Custom Field Function. In order to be confident with what I am doing, I am currently checking if the Custom Field Function I have written gives the same answer as the Report => Forces panel... and I am making one (or several) mistake(s) I am unable to detect. For the x component of the pressure force on the surface, I define a Custom Field Function as: p * x-surface- area and Sum over the surface on the Report => Surface Integrals. The result is very different from that I obtain using the Report => Force panel (it also disagrees with y and z components). Any help? Thanks, Toni

 February 9, 2011, 06:10 #2 Member   J.-H. Wang Join Date: Oct 2010 Location: Ithaca, New York Posts: 52 Rep Power: 6 Hi, Toni. I ran to the same problem with you. I'm wondering if we misunderstand the definition of "X Face Area" in the droplist of "Mesh" or something else, and neither do I know how Fluent calculate the integrals/sum in the surface monitor operation. This makes me really uncomfortable... If you already find the answer, could you share it some time? It would be helpful, thanks. JH

 February 10, 2011, 02:29 #3 Member   J.-H. Wang Join Date: Oct 2010 Location: Ithaca, New York Posts: 52 Rep Power: 6 Since that no one reponse to this question, I would answer it myself. First, I need to admit that "X Face Area" is a strange quantity and it seems no one know what it represents. Even the official manual is written in so abstruse language that I doubt that they cannot figure it out either... I have did some experiments on the quantity yet I still coulnd't get it. After spending hours, I quit on this thing. I temporarily use the monitor panel to obtain the force coefficient and it sucks because of the restrictions, anyway if there are people who have better advices I would be much appreciated. JH

April 13, 2011, 03:25
#4
New Member

qingkai
Join Date: Apr 2011
Posts: 11
Rep Power: 6
Hi， JH. Have you solved this problem now?
I have a similar question similar with you, and want to get some advices from you.
You know, in Force Report, we can get the force on Wall only. However, I need the force on Wall and another kind of boundary. So I used p*x-surface-area as you ever used before, but the result seems not reasonable.
Do you have any idea about my problem?

Quote:
 Originally Posted by f0208secretx Since that no one reponse to this question, I would answer it myself. First, I need to admit that "X Face Area" is a strange quantity and it seems no one know what it represents. Even the official manual is written in so abstruse language that I doubt that they cannot figure it out either... I have did some experiments on the quantity yet I still coulnd't get it. After spending hours, I quit on this thing. I temporarily use the monitor panel to obtain the force coefficient and it sucks because of the restrictions, anyway if there are people who have better advices I would be much appreciated. JH

 April 13, 2011, 03:34 #5 Member   J.-H. Wang Join Date: Oct 2010 Location: Ithaca, New York Posts: 52 Rep Power: 6 Actually we are taking different issues: I was stucked on the transient force report, while you are confused about outputting properties of the non-wall boundaries. What kind of boundaries are you handling here? Try to identify them in the pre-process procedure as an independent wall. That might help. JH

 April 13, 2011, 03:36 #6 Member   J.-H. Wang Join Date: Oct 2010 Location: Ithaca, New York Posts: 52 Rep Power: 6 One more thing, the x-surface-area and the x-face-area is tricky as it seems, you shall examine the mechanisms underlying carefully before utilization. Teach me when you figure it out. :-D

April 13, 2011, 04:03
#7
New Member

qingkai
Join Date: Apr 2011
Posts: 11
Rep Power: 6
Yeah, I set then as Velocity Inlet because I want to simulate the plasma on the surface. But when it is set as Velocity Inlet, cannot be set as Wall at the same time. I will try to figure out.

Quote:
 Originally Posted by f0208secretx Actually we are taking different issues: I was stucked on the transient force report, while you are confused about outputting properties of the non-wall boundaries. What kind of boundaries are you handling here? Try to identify them in the pre-process procedure as an independent wall. That might help. JH

 Tags custom field function, pressure forc

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