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Natural Convection - Boundary conditions

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Message 1 of 4
66462D
1015 Views, 3 Replies

Natural Convection - Boundary conditions

Hello!

I am having problems with setting up boundary conditions properly. The subject is natural convection.

I would like to have an open air volume with 2 solid walls (side and bottom). I set up the project and it works fine (image 1)

 

1.png

 

I also need to specify the temperature of 1 side wall to be 16 deg C. Ambient temperature must be 20 deg C. I have tried with many set up options but results are weird. The air flow is very different from results that I had with only ambient temperature set up to 20 deg C (image 2)

 

2.png

 

I even have tried with an extra wall with temperature/film coefficient boundary condition. (image 3)

 

3.png

 

 

Flag "use_property_ref_temp value" is set to 1 according to this soulution strategy guide:

 

http://knowledge.autodesk.com/support/simulation-cfd/learn-explore/caas/CloudHelp/cloudhelp/2015/ENU...

 

I would be grateful if someone could give me tips/solution how to set up scene/boundary conditions properly.

 

Thank you.

Pablo, Student.

 

3 REPLIES 3
Message 2 of 4
Jon.Wilde
in reply to: 66462D

Hi Pablo,

 

Your model looks over cosntrained to me, we should not need anything on the side walls (other than your fixed 20C - might a film coefficient be more realistic though?).

 

Please check out the guide here for how to set these models up - use the chimney approach.

 

Kind regards,

Jon

Message 3 of 4
66462D
in reply to: Jon.Wilde

Hi wildej, thank you for your answer.

 

I just wanted to simplify model in order to save time needed for solving . The situation I want to simulate is a radiator situated near one wall (which have temperature 16 deg C) when the air temperature is 20 deg C.

I followed THIS guides to set up film coefficient coundary condition on the top surface of the air. I also set those conditions to 3 other sides of the air to simulate situation when air comes from the side. Image 1 in the first post shows that it worked.

 

Do I have to model the room or there is other approach I could do to simulate this?

4.png

 

Pablo

Message 4 of 4
Jon.Wilde
in reply to: 66462D

Hi Pablo,

 

It is probably better to model the room and use a 'bucket' approach with just the conditions on the top surface of the air. P=0 and a Film Coefficient.

 

If you set all the walls open you will run into issues as we ideally want air only entering or exiting the domain over a P=0. If it recirculates we can end up with poor results.

 

Kind regards,

Jon

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