Huge difference in Hybrid vs Conservative values in BC

vbraga · September 6, 2016, 10:08

Hello, I'm getting a huge difference between the values of pressure in my Boundary Condition calculated by the Hybrid and Conservative methods. I know the difference between them, however I would expect both methods to provide values within certain range. Instead of that I'm getting 0.629 bar in the outlet for the Hybrid method (which is my actual BC), and rouhly 2 bar for the conservative method. Is this a sign that my mesh is not refined enough? I know for a fact that there's a significant pressure gradient at the outlet of my domain.

Best regards.

turbo · September 6, 2016, 15:49

If there is a significant pressure gradient at your outlet BC, and if the solution is well converged, I'd go with the conservative value because it is a part of solution while the hybrid is just your wish.

ghorrocks · September 6, 2016, 19:16

Hybrid and conservative values are only different in the volume adjacent to the wall. If you get such large differences between hybrid and conservative it suggests the volumes adjacent to the wall are a large proportion of the total boundary. This does not sound like a sufficiently fine mesh to me. But to be sure you should do a mesh sensitivity check.

September 6, 2016, 10:08	Huge difference in Hybrid vs Conservative values in BC	#1
vbraga New Member Vitor Braga Join Date: Jun 2016 Posts: 4 Rep Power: 9	Hello, I'm getting a huge difference between the values of pressure in my Boundary Condition calculated by the Hybrid and Conservative methods. I know the difference between them, however I would expect both methods to provide values within certain range. Instead of that I'm getting 0.629 bar in the outlet for the Hybrid method (which is my actual BC), and rouhly 2 bar for the conservative method. Is this a sign that my mesh is not refined enough? I know for a fact that there's a significant pressure gradient at the outlet of my domain. Best regards.

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
ATTENTION! Reliability problems in CFX 5.7	Joseph	CFX	14	April 20, 2010 15:45
max node values exceed max element values in contour plot	jason_t	FLUENT	0	August 19, 2009 11:32
huge difference in running time	Jimmy	Main CFD Forum	5	July 18, 2008 22:29
high difference between cell and nodal values	Trilok	FLUENT	2	November 13, 2003 03:38
Conservative finite difference scheme?	Linfeng BI	Main CFD Forum	1	October 10, 2002 12:17

September 6, 2016, 15:49		#2
turbo Senior Member Join Date: Jun 2009 Posts: 174 Rep Power: 16	If there is a significant pressure gradient at your outlet BC, and if the solution is well converged, I'd go with the conservative value because it is a part of solution while the hybrid is just your wish.

September 6, 2016, 19:16		#3
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,700 Rep Power: 143	Hybrid and conservative values are only different in the volume adjacent to the wall. If you get such large differences between hybrid and conservative it suggests the volumes adjacent to the wall are a large proportion of the total boundary. This does not sound like a sufficiently fine mesh to me. But to be sure you should do a mesh sensitivity check.