Learning Forum

[M Usman]

Hey How can I do CFD Analysis in Fluent in which inner surface of the hollow cylinder is at high temperature and then there is a conduction from the inner surface to the outer surface and air is flowing at a very high speed like 0.5 mach to cool the body through convective heat transfer. Right now I have been successfully ale to simulate the convective heat transfer from a hot body to the air by patching temperature value to the body. But now the temperature should be on the inner surace only and conduction and convection should happen simultaneously.

[Essence]

Hello,

You can try performing CHT by meshing the solid zone and applying the required temperature on the inner surface.

[M Usman]

The Conjugate heat transfer occurs by patching the temperature on the body or zone. If I apply temperature in wall boundary conditions on the surface, then that method does not work.

[Essence]

Then, why don't you do one thing? Create a very thin concentric cylinder at the inner surface of the already existing cylinder and patch that newly created cylinder with the desired inner surface temperature.

[M Usman]

Yes, I am currently simulating exactly this.

[M Usman]

Can you please specify which Viscous Model I should use to simulate this. Also how can I validate my results.

[Essence]

Well, that depends on many factors. I would suggest k-w SST which is a default model in Fluent and is recommended for many numerical simulations.

[M Usman]

My simulation works correctly when I use a simple hollow capped rod, but when I apply the same approach on actual barrel geometry, Floating Point Exception error occurs. Can you please guide regarding it.

[Essence]

If you observe the residuals, it clearly specifies divergence of the solution. Divergence can occur due to many reasons. For example, the mesh or the case setup.

[M Usman]

I tried multiples times, only CHT approach fails on this. Also meshing and Inflation are not a problem as per my experience and knowledge. Also can you explain about case setup?

[Essence]

Which version are you using? What material properties options have you chosen? Please specify what Methods and Controls you have set.

[M Usman]

I am using 2022 R2, Barrel Material is Steel chosen from Fluent Database. Fluid is air. Tried both K-omega and K-epsilon Viscous Models.

Materials:

Boundary Condiitions:

Air with 25 degree celcius temperature and 0.5 Mach Speed

Pressure Outlet

Walls:

Coupled

Method:

Controls (Default):

Patched Temperatur to very thin inner cylinder after initialization

[Essence]

Use SST k-w model. If the mesh is not so good, use Warped-Face Gradient correction, Use 10-50 Courant number until the solution gets stable and converges. Then gradually increase it till 100-150. Use First Order for the spatial discretization and once the solution gets converged, move on to second order. Reduce the URFs to 0.25 until the solution gets stable and converges. Then gradually increase to default. 

Try using temperature dependent properties for air instead of constant values.

[Essence]

Adding to my reply, I think you might need to fix the temperature values in the thin inner cylinder instead of patching it.

[M Usman]

I previously tried applying the temperature on wall but Conjugate Heat Transfer does not happen as result become constant. And then I got a suggestion from here that I should patch the temperature on the body and that worked and only because of this I have to create a very thin cylinder otherwise in actual, I only had to apply the temperature on the inner wall of the barrel.

[Essence]

 

I am referring to fix the temperature to the whole inner thin cylinder. You can do this in Cell Zone conditions. Patching is different.

 

[M Usman]

I have tried this approach as well but when I display the contours after initializing, the temperatures on the bodies do not get updated but when I patch the temperature, contours get updated. Also the recommendations you wrote to avoid the floating point exceptionor divergence worked in one case but when I slightly changed the geometry, the same error is appearing again. I have tried changing method and oter parameters but nothing worked.

[Essence]

Did you check them after running the case for few iterations after fixing and initializing?

For divergence, it shows that, there maybe some defects which needs to be repaired. As I told you, there are many reasons for that.

[M Usman]

Ok sure I will check