Heat transfer problem at fluid-solid interface

kiwikiwi · January 8, 2013, 22:31

Hi everyone,

I'm learning Fluent and I'm trying to model transient heat transfer from a metal cylinder to air by natural convection. I'm having trouble with interfaces and I'm not sure on the best approach, hopefully you can help. I am using Workbench 14.5, DesignModeler, ANSYS Meshing and of course Fluent. Here is what I have done.

1. Create a cylinder(solid) in DM
2. Create a box (fluid) which is larger than, and surrounds the cylinder
3. Boolean subtract of the cylinder from the box whilst preserving the tool body (the cylinder)
4.Created 3 named selections; cylinder, env, hotface. env represents the environment which is air and hotface is one end of the cylinder which will have a heat flux applied to it.

5. I mesh this using the Workbech Meshing program using default settings, a contact region with 3 faces is detected

6. In Fluent, 3 wall boundary conditions are created; hotface, wall-cylinder and wall-env.
7. I apply gravity, incompressible-ideal-gas (as an air property) and a heatflux to hotface.

Result: there is heat transfer to the cylinder but none to the environment.

Ideas: I have changed the Zones 'wall-cylinder' and 'wall-environment' to interfaces, created a mesh interface using these and got convection happening. Fluent creates 3 walls and a single corresponding shadow wall when I do this. This seems a bit messy as when I create the mesh interface there are 3 faces for 'wall-cylinder' and 9 faces for 'wall-env' (3 from the cylinder and 6 from the box.

What is the best way to approach this problem?

Thanks in advance

kiwikiwi · January 14, 2013, 15:31

Alright so I figured out that a much simpler way is to form all bodies into a single part in DesignModeler and then coupled walls and shadow walls are created as there is a conformal mesh. Much easier!

Markat · January 14, 2013, 17:12

You could also mesh only the fluid (do not preserve booleans tool body) an use a shell conduction approach to model conduction in the cylinder.

Markat · January 14, 2013, 17:13

Quote:

Originally Posted by kiwikiwi

Alright so I figured out that a much simpler way is to form all bodies into a single part in DesignModeler and then coupled walls and shadow walls are created as there is a conformal mesh. Much easier!

This is really a best practice when you to mesh both fluid and solid

kiwikiwi · January 14, 2013, 18:47

Many thanks for your advice Markat, so much to learn and sometimes the User's guide doesn't spell out the basic things like this.
Cheers!

January 8, 2013, 22:31	Heat transfer problem at fluid-solid interface	#1
kiwikiwi New Member Join Date: Jan 2013 Location: New Zealand Posts: 5 Rep Power: 13	Hi everyone, I'm learning Fluent and I'm trying to model transient heat transfer from a metal cylinder to air by natural convection. I'm having trouble with interfaces and I'm not sure on the best approach, hopefully you can help. I am using Workbench 14.5, DesignModeler, ANSYS Meshing and of course Fluent. Here is what I have done. 1. Create a cylinder(solid) in DM 2. Create a box (fluid) which is larger than, and surrounds the cylinder 3. Boolean subtract of the cylinder from the box whilst preserving the tool body (the cylinder) 4.Created 3 named selections; cylinder, env, hotface. env represents the environment which is air and hotface is one end of the cylinder which will have a heat flux applied to it. 5. I mesh this using the Workbech Meshing program using default settings, a contact region with 3 faces is detected 6. In Fluent, 3 wall boundary conditions are created; hotface, wall-cylinder and wall-env. 7. I apply gravity, incompressible-ideal-gas (as an air property) and a heatflux to hotface. Result: there is heat transfer to the cylinder but none to the environment. Ideas: I have changed the Zones 'wall-cylinder' and 'wall-environment' to interfaces, created a mesh interface using these and got convection happening. Fluent creates 3 walls and a single corresponding shadow wall when I do this. This seems a bit messy as when I create the mesh interface there are 3 faces for 'wall-cylinder' and 9 faces for 'wall-env' (3 from the cylinder and 6 from the box. What is the best way to approach this problem? Thanks in advance

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January 14, 2013, 15:31		#2
kiwikiwi New Member Join Date: Jan 2013 Location: New Zealand Posts: 5 Rep Power: 13	Alright so I figured out that a much simpler way is to form all bodies into a single part in DesignModeler and then coupled walls and shadow walls are created as there is a conformal mesh. Much easier!

January 14, 2013, 17:12		#3
Markat New Member Join Date: Oct 2012 Posts: 27 Rep Power: 13	You could also mesh only the fluid (do not preserve booleans tool body) an use a shell conduction approach to model conduction in the cylinder.

January 14, 2013, 18:47		#5
kiwikiwi New Member Join Date: Jan 2013 Location: New Zealand Posts: 5 Rep Power: 13	Many thanks for your advice Markat, so much to learn and sometimes the User's guide doesn't spell out the basic things like this. Cheers!