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

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]

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

[BHOLU KUMAR]

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]

Originally Posted by BHOLU KUMAR

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]

Originally Posted by BHOLU KUMAR

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]

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.