Solid-Solid-Fluid heat transfer issue

DitchBah · March 18, 2023, 07:53

Hello everyone,

I am trying to create a simplified engine cylinder-piston system. My ultimate goal is to analyze different deformation values along the cylinder due to uneven air cooling. However I cannot seem to get past the first step, which is to have that temperature profile as a result of air flow around the cylinder.

I managed to produce said profile when modeling a simple enclosure with a cylinder running through it. However, I cannot replicate that with a proper cylinder with a thickness, or in other words a proper solid. Seemingly tried all possible options inside CFX but cannot seem to create a proper simulation. Now the temperature profile is pretty constant, air is one temperature, cylinder another and piston another, they do not seem to have any interaction with each other.

Do I need to have an interface defined for each contact surface? If yes, then how do I set a temperature or heat source to a body? Because once interface is set I cannot input a temperature to a surface as CFX says that that surface is already in use for another boundary condition.

In essence I would like to have the simplified piston to generate heat, transfer it to the cylinder and for the cylinder to be cooled with air flow.

Could anyone please point me in the right direction? Provide advice, tutorial or any other sort of help.
Anything would be highly appreciated as I have been stuck on this for quite too long.

ghorrocks · March 18, 2023, 22:22

My PhD thesis was on a CFD model of an IC engine: https://opus.lib.uts.edu.au/handle/2100/248

I got it all working

Modelling IC engines is not simple and should only be attempted if you have a good background in CFD. Otherwise you are not going to get far. Also - modelling heat transfer in IC engines is even more challenging and is a topic of research (this means there is no "button" to press to activate an accurate heat transfer model, you have to develop it yourself for your specific case).

Start simple - do compression of a simple box or cylinder, with no valves or anything. Use moving mesh to do the compression and see how accurately you can get the air temperature to follow the ideal gas adiabatic compression curve. This will teach you a lot about mesh motion and simulation accuracy.

Modelling poppet valves is a challenging topic by itself. But don't start here, do the compression first.

DitchBah · March 25, 2023, 10:51

Hi Ghorrocks,

Thanks for replying.
I am aware that IC engine modelling is quite challenging and as mentioned this model will be simplified. For now I am not trying to simulate gas combustion.

Right now the model is very basic. Heat is supposed to be added to the inner cylinder (simplified piston), which in turn transfers heat to the outer cylinder, which is being cooled by airflow.

I managed to get a model working when there is only 1 domain. As soon as I add a second domain it all falls apart.

ghorrocks · March 26, 2023, 00:22

That does not sound like the sort of IC engine I am familiar with. Can you please attach some images of what you are modelling? What are the inner and outer cylinders? How does it function? Why are you interested in the heat transfer of this device?

March 18, 2023, 07:53	Solid-Solid-Fluid heat transfer issue	#1
DitchBah New Member Domantas Join Date: Mar 2023 Posts: 2 Rep Power: 0	Hello everyone, I am trying to create a simplified engine cylinder-piston system. My ultimate goal is to analyze different deformation values along the cylinder due to uneven air cooling. However I cannot seem to get past the first step, which is to have that temperature profile as a result of air flow around the cylinder. I managed to produce said profile when modeling a simple enclosure with a cylinder running through it. However, I cannot replicate that with a proper cylinder with a thickness, or in other words a proper solid. Seemingly tried all possible options inside CFX but cannot seem to create a proper simulation. Now the temperature profile is pretty constant, air is one temperature, cylinder another and piston another, they do not seem to have any interaction with each other. Do I need to have an interface defined for each contact surface? If yes, then how do I set a temperature or heat source to a body? Because once interface is set I cannot input a temperature to a surface as CFX says that that surface is already in use for another boundary condition. In essence I would like to have the simplified piston to generate heat, transfer it to the cylinder and for the cylinder to be cooled with air flow. Could anyone please point me in the right direction? Provide advice, tutorial or any other sort of help. Anything would be highly appreciated as I have been stuck on this for quite too long.

March 18, 2023, 22:22		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,852 Rep Power: 144	My PhD thesis was on a CFD model of an IC engine: https://opus.lib.uts.edu.au/handle/2100/248 I got it all working Modelling IC engines is not simple and should only be attempted if you have a good background in CFD. Otherwise you are not going to get far. Also - modelling heat transfer in IC engines is even more challenging and is a topic of research (this means there is no "button" to press to activate an accurate heat transfer model, you have to develop it yourself for your specific case). Start simple - do compression of a simple box or cylinder, with no valves or anything. Use moving mesh to do the compression and see how accurately you can get the air temperature to follow the ideal gas adiabatic compression curve. This will teach you a lot about mesh motion and simulation accuracy. Modelling poppet valves is a challenging topic by itself. But don't start here, do the compression first. Opaque likes this. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

March 26, 2023, 00:22		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,852 Rep Power: 144	That does not sound like the sort of IC engine I am familiar with. Can you please attach some images of what you are modelling? What are the inner and outer cylinders? How does it function? Why are you interested in the heat transfer of this device? __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

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March 25, 2023, 10:51		#3
DitchBah New Member Domantas Join Date: Mar 2023 Posts: 2 Rep Power: 0	Hi Ghorrocks, Thanks for replying. I am aware that IC engine modelling is quite challenging and as mentioned this model will be simplified. For now I am not trying to simulate gas combustion. Right now the model is very basic. Heat is supposed to be added to the inner cylinder (simplified piston), which in turn transfers heat to the outer cylinder, which is being cooled by airflow. I managed to get a model working when there is only 1 domain. As soon as I add a second domain it all falls apart.