Learning Forum

[aliborhan]

Hi all,

In Ansys-Fluent, is there a boundary condition that can specify both the normal velocity and species mass fraction?

I tried the velocity-inlet boundary condition, and hooked my udf for the species. However, it's not allowing me to set it properly because the flow is opposite of the inlet (backflow). If I do it on a wall boundary condition, then I can't set a leak velocity. 

This happens if I want to set a temperature profile too.

Thank you!

[Essence]

Hello,

Normally, you should not get the backflow near the inlet. This happens due to incorrect case setup. Can you share the screenshot of the backflow near the inlet?

[aliborhan]

Hi,

Sorry for the confusion. I am trying to model a pipe flow with a porous media using 2D axisymmetric. The interior in Fig 1 does not allow me to hook a udf for the species, therefore, I want to use the inlet-velocity boundary condition on the wall 2 (interior in figure 1) in figure 2 to model both the flow through the porous media and hook my species udf. By hooking the udf, it would allow me to see the concentration profile near the wall 2 in figure 2.

As I mentioned before, the flow out is the opposite of what the velocity inlet boundary condition wanted, therefore, the species udf would not be used. Ansys used the upstream cells to model it. I would like to know if there is a boundary condition or a way that allows me to hook both a velocity and species udf on a boundary.

Thank you!

[Essence]

 

Hello,

First of all you do not need to apply velocity udf or velocity profile as a boundary condition at wall 2. The pressure outlet condition is sufficient. Another thing is about the species concentration, you can provide the species boundary condition at inlet itself. Now, choose the porous media such that it is permeable only to the species you want it to be (this can be done in the Fluent settings). Therefore, you will get the species concentration data wherever you want in the domain. You might find more information here: https://ansyshelp.ansys.com/Views/Secured/corp/v231/en/flu_ug/flu_ug_bcs_sec_cell_zones.html?q=porous%20media

https://ansyshelp.ansys.com/Views/Secured/corp/v231/en/flu_ug/tgd_user_workflow_guided_tasks_create_porous_regions.html?q=porous%20media

https://ansyshelp.ansys.com/Views/Secured/corp/v231/en/flu_tg/flu_tg_tut_catalytic_converter.html?q=porous%20media

Please let me know if this helps.

 

[aliborhan]

Hi,

Thank you for your response. Could you please provide more details about how I can make a specie permeable/impermeable in the porous media? I read through the materials you provided, however, I am not able to set separate permeabilities for different species inside the porous zone. The only material that is allowed in the porous zone is the mixture, otherwise it will have an error.

Thank you!

[Essence]

 

Hello,

You can create separate cell zones and assign them required porous zones, thus the required properties. You can create the different cell zones while modeling itself.

 

[aliborhan]

Hi,

Thank you for the quick response. However, is it possible to set different permeabilities for different species in the one cell zone (porous media)? If not, how can I make one specie impermeable in one cell zone while the other species can move across freely.

Thank you.

[Essence]

Hello,

You can make use of "Viscous resistance (Inverse absolute permeability)", "inertial resistance" and "power law" to specify the required permeabilities. For more info on how to use them, please refer the user's manual provided earlier.

[aliborhan]

Hi,

Thank you for the response. I already know how to set the permeabilities with those options.  I would not need to specify inertial resistance and power law since the flow is laminar. The problem is that only "mixture" can be used for the material in the porous zone, therefore, I can only specify the permeability for the "mixture".

The goal is to specify different permeabilities for different species inside the mixture. I hope the question is explained clearly.

Thank you again.