
[Sponsors] 
April 7, 2012, 11:06 
momentum loss

#1 
New Member
suong
Join Date: Apr 2012
Posts: 7
Rep Power: 6 
hi
Can someone tell me: how to calculate energy or momentum of fluid loss behind the cylinders. ( flow past the cylinder) thank so much! 

April 7, 2012, 16:19 

#2 
Member
banty
Join Date: Mar 2012
Posts: 52
Rep Power: 6 
Hi,
U can write a UDF for energy calculation at particular time E = (rho* Velocity*Velocity)/2 

April 8, 2012, 10:18 

#3 
New Member
suong
Join Date: Apr 2012
Posts: 7
Rep Power: 6 
Thank a lot, and I think i must spent more time to learn UDF. i'm a beginner


April 8, 2012, 13:16 

#4  
Senior Member
Join Date: Jul 2009
Posts: 245
Rep Power: 10 
Quote:
That's not the exact command because you have to define that point in either Fluent or in CFD post. If you want to calculate the average momentum or energy in a volume, you need to cut that volume out of the domain. If that's what you want to do, I'll help further. 

April 8, 2012, 22:49 

#5 
New Member
suong
Join Date: Apr 2012
Posts: 7
Rep Power: 6 
Thank a lot kingjewel1. Yes, i want to calculate the average momentum or energy . Can use help me how to cut that volume out of the domain and how to calculate it, more detail, please..


April 9, 2012, 05:25 

#6 
Senior Member
Join Date: Jul 2009
Posts: 245
Rep Power: 10 
When you say you want to calculate the average momentum loss behind a cylinder what exactly do you mean? can you draw it for us?
Is it the momentum you want to calculate in a given volume behind the cylinder? If that's the case what you need to do is decide what size this volume needs to be and the bounding coordinates (x0 y0 z0) and (x1 y1 z1). Go to Adapt Region  Put in those coordinate and click MARK. Then go to Mesh Separate Zones choose the two fluid zones you want to split and that's your volume created. It's still perfectly transparent to the fluid, just has a separate name. Then go to Report/Volume/VolumeAverage choose which volume you want to calculate in (ie your new one) and then choose your variable. Since you have a particular equation, you need to define this first in Custom Field Functions for it to appear in the list available in report. You can also set this as a volume monitor during calculation eg for a convergence criterium. Hope that helps. 

April 11, 2012, 07:55 

#7 
New Member
suong
Join Date: Apr 2012
Posts: 7
Rep Power: 6 
thank you for replying
it is very useful. I did it. 

Thread Tools  
Display Modes  


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
momentum loss equation porous media  pato  CFX  1  March 21, 2012 19:28 
Momentum source / porous loss  ijk  CFX  5  May 20, 2011 10:30 
Derivation of Momentum Equation in Integral Form  Demonwolf  Main CFD Forum  2  October 29, 2009 20:53 
2D momentum source for pressure loss  Bernhard Dobmeier  CFX  0  December 5, 2006 05:05 
Experts in momentum loss please help  jemteo  CFX  7  March 15, 2006 23:42 