topic Re: assign two boundary conditions for an inlet in CFD Forum

assign two boundary conditions for an inlet

modess.seyednezhad — Tue, 20 Sep 2022 19:08:11 GMT

I am trying to define velocity and temperature for the inlet, but for some reason, I am only able to define one of them at a time. Any suggestion?

Re: assign two boundary conditions for an inlet

karol.suchon — Wed, 21 Sep 2022 12:31:54 GMT

Every BC are applied separately. So if you have a velocity, click on the surface, edit and change the boundary condition to temperature pressure etc. The software keeps the previous Boundary condition to the moment when you do not remove it.

Karol

Re: assign two boundary conditions for an inlet

modess.seyednezhad — Mon, 26 Sep 2022 14:52:03 GMT

Thank you, Karol!

I could successfully apply both Velocity and Temperature BC to the inlets, but for some reason, I cannot see any changes to the fluid!

It seems that the BC is only applied to the surface, not to the volume!

Re: assign two boundary conditions for an inlet

karol.suchon — Mon, 26 Sep 2022 14:57:15 GMT

Hello,

please check if you enable the heat transfer in the solver bar. Solve->Physics, if you have natural convection also do not forget about the gravity vector and setting the material as a variable, to detect the density changes.

Karol

Re: assign two boundary conditions for an inlet

modess.seyednezhad — Mon, 26 Sep 2022 15:00:08 GMT

I enabled that. It is forced convection.

Re: assign two boundary conditions for an inlet

modess.seyednezhad — Mon, 26 Sep 2022 15:00:41 GMT

How can I set the material as a variable?

Re: assign two boundary conditions for an inlet

karol.suchon — Mon, 26 Sep 2022 15:09:42 GMT

If you have auto-forced convection you should not set material as a variable, you do not want to compute the density change on the velocity field.

You could set the variable by clicking on RMC on the material and selecting edit material environment reference, there you could set it as a variable.

AutoForced convection first computes the velocity and pressure field, and later computes the temperature distribution. There is a chance that the second step was not computed yet.

Karol

Re: assign two boundary conditions for an inlet

modess.seyednezhad — Mon, 26 Sep 2022 15:13:23 GMT

Each inlet in this model has velocity normal, volume flow rate, and temperature as the boundary conditions.

The outlet has a pressure of zero and all walls have a heat flux of zero which represents insulation BC.

In steady state conditions, I still see no changes in temperature along the channel!!

Re: assign two boundary conditions for an inlet

modess.seyednezhad — Mon, 26 Sep 2022 15:16:29 GMT

Do I need to define unknown BC for the outlet?

Re: assign two boundary conditions for an inlet

karol.suchon — Mon, 26 Sep 2022 15:17:41 GMT

You could attach the zip file of the simulation.

But from the description of the boundary condition, you could only have two solutions constant fluid(equal to BC temperature and solid temperature( solid probably 0, or constant temperature in the entire geometry equal to BC, depending on where you applied 0 heat flux.

Karol

Re: assign two boundary conditions for an inlet

modess.seyednezhad — Mon, 26 Sep 2022 15:20:14 GMT

Here is the zip file. Could you please see where the problem is?

Thank you,

Re: assign two boundary conditions for an inlet

karol.suchon — Mon, 26 Sep 2022 15:21:39 GMT

No, absolutely do not apply an unknown BC.

That is the special BC applied only for internal compressible flow.

Send me the model and I will check it, but if that is your first attempt at CFD simulation, I will strongly recommend starting from the tutorial, and a few exercises and you could work with the software without frustration.

Karol

Re: assign two boundary conditions for an inlet

karol.suchon — Mon, 26 Sep 2022 15:22:41 GMT

Please use that method to share the file with me.

Re: assign two boundary conditions for an inlet

modess.seyednezhad — Mon, 26 Sep 2022 15:27:42 GMT

Yes, this is my first time working with Autodesk CFD. Unfortunately, the tutorials were not useful for me.

Please see the attached file.

Re: assign two boundary conditions for an inlet

karol.suchon — Mon, 26 Sep 2022 15:52:20 GMT

Ok, I am not sure but probably you stopped the simulation during the first stage of auto-forced convection manually.

As I mentioned earlier, the first stage of auto-forced convection does not compute heat transfer. That is the reason why the simulation has a constant temperature. Also, the condition of the outlet walls is not necessary, by default the wall is adiabatic.

I attached the simulation with and without auto-forced convection and for both scenarios, we get the temperature gradient.

Karol

Re: assign two boundary conditions for an inlet

modess.seyednezhad — Mon, 26 Sep 2022 16:25:09 GMT

Dear Karol,

Thank you for assisting me.

May I know what did you change except the auto-forced convection in the result dialog box?

Did you change the boundary conditions?

Re: assign two boundary conditions for an inlet

karol.suchon — Mon, 26 Sep 2022 16:56:50 GMT

The Autoforced convection works in the third scenario also. I deleted the heat flux boundary condition, on the outside wall he is applied by defoult.

Karol

Re: assign two boundary conditions for an inlet

modess.seyednezhad — Mon, 26 Sep 2022 16:58:11 GMT

I appreciate it!

Re: assign two boundary conditions for an inlet

karol.suchon — Mon, 26 Sep 2022 17:01:38 GMT

If you do not have other questions you could accept the solution 🙂

It always better if the thread has the green accept sign 🙂

Re: assign two boundary conditions for an inlet

modess.seyednezhad — Tue, 27 Sep 2022 15:25:15 GMT

I have another question. I increased the thermal conductivity and I expect to have a higher temperature drop but it was vice versa. I am not sure what is not working and I do not know how to debug it.