CFD Online Discussion Forums

CFD Online Discussion Forums (http://www.cfd-online.com/Forums/)
-   FLUENT (http://www.cfd-online.com/Forums/fluent/)
-   -   Backflo direction specification method (http://www.cfd-online.com/Forums/fluent/50520-backflo-direction-specification-method.html)

vijay February 9, 2009 18:30

Backflo direction specification method
 
Can any one tell me what is back flow direction specification method in pressure outlet boundary condition window?

Alagesanj February 10, 2009 09:32

Re: Backflo direction specification method
 
Hi Vijay,

If there is any reverse flow in your model then you may need to specify the back flow specification method. Otherwise just leave the default setting "normal to Boundary". You can refer fluent 6.3 User guide for further details.

Cheers, Alagesan.

mfim88 August 5, 2015 05:30

Can anyone tell me when we should use the option "from neighboring cell" for backflow direction specification method.?

BHOLU KUMAR August 27, 2015 02:35

Back flow direction specification method
 
I have also the almost same problem, In backflow direction specification method by taking normal to boundary, Is it sure to no backflow ? In my case while taking pressure inlet bcs, the pressure at inlet is changes by small amount at the end of the simulation. Why it is happening ?

Bruno Machado August 27, 2015 06:23

Quote:

Originally Posted by BHOLU KUMAR (Post 561269)
I have also the almost same problem, In backflow direction specification method by taking normal to boundary, Is it sure to no backflow ? In my case while taking pressure inlet bcs, the pressure at inlet is changes by small amount at the end of the simulation. Why it is happening ?

the backflow specifications should be set as an approximation of the values you are expecting in the outlet, so then Fluent use it to avoid backflow. The closer you set backflow values from expected, bigger chances to avoid backflow in your problem.

LuckyTran August 27, 2015 12:03

Quote:

Originally Posted by BHOLU KUMAR (Post 561269)
I have also the almost same problem, In backflow direction specification method by taking normal to boundary, Is it sure to no backflow ? In my case while taking pressure inlet bcs, the pressure at inlet is changes by small amount at the end of the simulation. Why it is happening ?

The backflow direction specification is to specify the direction of the backflow in case there is any backflow. Since you are not solving the flow outside the domain explicitly, if backflow occurs for any reason, you do not know the direction of the flow as you did not solve for it.

The available options are to assume the backflow is normal to the boundary, or you can specify the direction yourself. The third option is to assume the backflow is parallel (but opposite) to the flow in neighboring cells.

BHOLU KUMAR August 27, 2015 12:29

CFD Simulation of Human Respiratory Tract
 
In my simulation with airflow through human airways, I have taken pressure inlet and pressure outlet bcs. At the end of simulations I found the pressure was not same as I was fixed at inlet. I faces the problem in both cases of inhalation and exhalation and in both cases it is varying at inlet only. The bcs are not supposed to change. Why it is changing ? I want to fixed it? Please someone help me.


All times are GMT -4. The time now is 17:24.