Learning Forum

[klara.marek]

The problem depicted is a cubical cavity filled with air. The left wall of the domain is cold with a fixed temperature, the left wall is cold with a fixed temperature. Goal of this simulation is to visualize the natural convection occurring in a setup like this. The walls on top, bottom, front and back are insulated walls. The temperature difference between warm and cold wall is small, the Boussinesq Approximation therefor to my knowledge applicable. Ideally I would like to set the fluid material to air as an ideal fluid. Is air in the discovery library acting like an ideal fluid? Furthermore, since buoyancy and gravity are relevant for this simulation, I was wondering what the default value for the gravity was and if it is possible to change it anywhere? Since I would like to calculate natural convection for different Rayleigh Numbers, I would like to specify a reference density and operating pressure for my system. Is there a way to implement this in Discovery? If not, what is the default operating pressure and density used in fluid simulations? Thank you very much for all comments, clarifications and inputs regarding this problem!

[Charudatta Bandgar]

Hello Klara ,

I am looking into your query, will get back to you as soon as possible.

Regards.

[Charudatta Bandgar]

Hello Klara ,

The problem depicted is a cubical cavity filled with air.

This problem is possible in Discovery Explore mode, but the accuracy of the solution might not be that well. Although, it is soon to be released in Refine mode in the next release.  

The left wall of the domain is cold with a fixed temperature, the left wall is cold with a fixed temperature....The walls on top, bottom, front and back are insulated walls.

This can be done by defining wall conditions and defining thermal conditions for them (with temperatures on two walls and insulated on the remaining as shown below  

Furthermore, since buoyancy and gravity are relevant for this simulation, I was wondering what the default value for the gravity was and if it is possible to change it anywhere?

You can define and modify gravity by double-clicking gravity in the physics tree, and you can activate the buoyancy effect from there.

I would like to specify a reference density and operating pressure for my system. Is there a way to implement this in Discovery? If not, what is the default operating pressure and density used in fluid simulations?

You can not specify the reference density, it will be constant, defined in the material definition. Whereas operating pressure will be 1bar, which can not be changed/modified. This is still a limitation with Discovery, and hence the results might be inaccurate. Please let me know if this answers your query. If further in-depth information is needed, I will discuss it with the expert and will let you know. Regards.

[klara.marek]

Hello Charudatta Bandgar 

Thank you very much for all the information provided, this was already immensely helpful!

So if I understood correctly, the fluid in this simulation is considered to behave like an ideal gas with the constant density specified in the material details used for solving the temporal and convection terms and the changes in density will be calculated via the change in temperature (when buoyancy is activated, in the buoyancy term)? 

Also I was wondering if it was possible to apply an emissivity to the walls as well? I only saw this option in combination with the convection boundary condition and was unsure if setting the convection and radiation temperatures to either the cold or warm wall temperature would result in the same outcome as applying an emissivity to a wall with constant temperature. 

Again, thank you for your help! 

[Charudatta Bandgar]

Hello Klara

So if I understood correctly, the fluid in this simulation is considered to behave like an ideal gas with the constant density specified in the material details used for solving the temporal and convection terms and the changes in density will be calculated via the change in temperature (when buoyancy is activated, in the buoyancy term)? 

That is very correct.

Also I was wondering if it was possible to apply an emissivity to the walls as well? I only saw this option in combination with the convection boundary condition and was unsure if setting the convection and radiation temperatures to either the cold or warm wall temperature would result in the same outcome as applying an emissivity to a wall with constant temperature. 

Yes, you can define emissivity, by selecting convection with radiation, which will open the option to define the wall emissivity (ε) and radiation temperature. Regards.

[klara.marek]

Charudatta Bandgar Thank you very much for your help!