Boundary Condition for Natural Convection

  • 861 Views
  • Last Post 24 July 2018
cha10 posted this 08 May 2018

Hello,

I want to simulate air flow around heated/cooled body due to the natural convection. I am not really sure how to put the boundary conditions.

Here are what I think

1. Assign the temperature to the body, 2. no heat flux to the ground, 3. Pressure-inlet at the top boundary, pressure-outlet at the side. 

Are these fair boundary conditions? 

Thank you!

Order By: Standard | Newest | Votes
Raef.Kobeissi posted this 13 May 2018

Yes but you need to make sure that the ideal gas is selected and also the Boussinesq Parameter is set up. Please see figures below:

Raef Kobeissi

  • Liked by
  • gishnutr
  • peteroznewman
gishnutr posted this 24 May 2018

Hi, Raef

       I your comment above, you mentioned to use ideal gas as material. I have three doubts in this.

  1. The incompressible-ideal gas also have same values in the given tab. Is it just a incompressible fluid/ flow version of ideal gas model or is there any other explanation for using these two?

2. If Boussinesq parameter is set up in Operating conditions tab, then what is the use of the Boussinesq term in Density model selection under Edit Material  tab? 

3. In Operating conditions tab the operating density id given as "0". By default the value is 1.225. Why is it changed to 0?

 

Thank you.

Kremella posted this 24 July 2018

Hello,

To answer your questions:

1. An incompressible-ideal gas law is used to estimate the density of an INCOMPRESSIBLE fluid using the ideal gas law (check out section 7.3.6., Fluent User's Guide).

2. The density drop down in the material property panel allows you to choose the Boussinesq approximation model and it uses a constant value of density by writing the buoyancy term as a function of operating temperature (section 12.2.4.2, Fluent User's Guide). You will also have to specify thermal expansion coefficient (beta).

3. Operating density is non-zero because it appears in the body-force term of the momentum equation. When Boussinesq approximation is used, this value becomes irrelevant and therefore need not be specified. Care should be taken while specifying the operating density (section 12.2.4.5, Fluent User's Guide).

I hope this helps.

Best Regards,

Karthik

Close