peteroznewman
posted this
29 November 2018

- Last edited 29 November 2018
**@rwoolhou**, this is a closed box, though the images above didn't show that. Using an ideal gas, as the temperature increases, the pressure will increase in the fixed volume. Does a fixed volume change your suggestion for using incompressible ideal gas for density? Is Pressure-Based solver appropriate, or would the Density-Based solver be better? I'm guessing Density, but correct me if I am wrong.

Dear Moda,

The body called air is meshed as a fluid for the Fluent solver, which means that each cell has a temperature, pressure and **velocity vector** computed as part of the solution. As I suggested, and rwoolhou has confirmed, gravity must be turned on.

With gravity turned on, *natural convection* will develop in the solution by heat transfer to the air near the wall, reducing its density. Gravity will pull the colder, heavier air in the center down, which pushes the warmer, lighter air near the wall upward. That means you have to edit air and change density from a constant, to **ideal-gas** or something else as suggested by the experts.

So in the steady state solution you can plot the *upward velocity of air near the wall, *while there would be a downward velocity in the center creating a big swirl pattern. With the above settings, it will take more than 1000 iterations to converge.

Here is a slice at x=40mm through the volume plotting the Y velocity component in cm/s

I would be interested to run a Transient solution and see the still air begin to flow to better visualize the convection, but that takes longer to compute than the steady-state solution.

Regarding the 5 wedges, since they have no connection to each other or to the main air cavity, they all will behave identically, so you can just mesh one wedge to see what happens in any wedge.

You can show your appreciation by clicking **Like** below the posts that are helpful. If your original question on zero thickness walls has been answered, you can click **Is Solution** on the post that best answered the question. Open a New Discussion to ask about computing Natural Convection. You can use a link in that new post to point back to this for background.

Regards,

Peter