[han08560]

Hello!
I am writing this because I am having trouble modeling natural convection in cfx-pre
A heat exchange occurs in the middle of the fluid flow, and the heat exchange causes a density difference in the fluid. This density difference creates buoyancy, and I want to simulate natural convection due to buoyancy.
I set opening and opening pressure as inlet boundary conditions, and opening and static pressure as outlet boundary conditions.

I ran the calculation for two cases.

1. Without heat exchange
2. With heat exchange

However, the flow rate was the same in both cases.
So I think the buoyancy due to the density difference is not calculated. Please help me.

[FMDenaro]

Originally Posted by han08560

Hello!
I am writing this because I am having trouble modeling natural convection in cfx-pre
A heat exchange occurs in the middle of the fluid flow, and the heat exchange causes a density difference in the fluid. This density difference creates buoyancy, and I want to simulate natural convection due to buoyancy.
I set opening and opening pressure as inlet boundary conditions, and opening and static pressure as outlet boundary conditions.

I ran the calculation for two cases.

1. Without heat exchange
2. With heat exchange

However, the flow rate was the same in both cases.
So I think the buoyancy due to the density difference is not calculated. Please help me.

From what you wrote, no one can say about your post.
Are you using the Bousinnesq approximation? What kind of formulation of the solver?
Have you already tried what happens in a closed domain?

[han08560]

Originally Posted by FMDenaro

From what you wrote, no one can say about your post.
Are you using the Bousinnesq approximation? What kind of formulation of the solver?
Have you already tried what happens in a closed domain?

I apologize for the lack of information in my question.

I am still a cfx beginner, so please understand.

I am modeling a natural convection cooling system using outside air.

It is a model where outside air is introduced through the inlet, the heated air that has undergone heat exchange is discharged through the outlet.

I gave the flow rate to the inlet and the pressure boundary condition to the outlet and analyzed it. In this case, it converged without any problems.

I used the ideal gas in cfx for air.

Should I use the Bousinnesq approximation even if I use the ideal gas?

I performed the analysis using the k-e model.

And I set the gravity setting to use the buoyancy option.

I wonder if I should set the buoyancy turbulence to production in cfx-pre.

Lastly, I am analyzing it in the steady state, but I am also wondering if I should analyze it in the transient state.

[FMDenaro]

Originally Posted by han08560

I apologize for the lack of information in my question.

I am still a cfx beginner, so please understand.

I am modeling a natural convection cooling system using outside air.

It is a model where outside air is introduced through the inlet, the heated air that has undergone heat exchange is discharged through the outlet.

I gave the flow rate to the inlet and the pressure boundary condition to the outlet and analyzed it. In this case, it converged without any problems.

I used the ideal gas in cfx for air.

Should I use the Bousinnesq approximation even if I use the ideal gas?

I performed the analysis using the k-e model.

And I set the gravity setting to use the buoyancy option.

I wonder if I should set the buoyancy turbulence to production in cfx-pre.

Lastly, I am analyzing it in the steady state, but I am also wondering if I should analyze it in the transient state.

So, you are using a fully compressible flow model? That would require more BC.s than only the velocity inlet.
Have you tried the incompressible flow model with Bousinnesq?
What about the characteristic parameter of the flow, is it really turbulent?