Moving mesh and thermodynamic issues...

loook · April 4, 2014, 02:32

Hi,

I am working on simulations with moving meshes. I have noticed several strange things using moving mesh:

I did simple simulation of a piston which first compress the gas and then moving backward letting gas to expand. There is no heat flux, just motion of a mesh. When I monitor the pressure and total volume I do get positive work!!? How is it possible...?

The other thing is heat flux through moving boundary. I have made the "total heat flux report" on each of boundaries and I have noticed relatively large heat flux through my moving boundary (even so it is set to adiabatic) why is that?

I did it via Report/Fluxes/TotalHeatTransferRate - does any body know how to monitor this particular flux and write it to file? ( i tried surface integrals... averaging and non of those gives me this strange flux)

I will be appreciated for help with those problems...

Bionico · April 4, 2014, 04:37

Hi loook,
have you tried disabling Energy from Equation menu?

Regards

loook · April 4, 2014, 04:58

no I did not, because I need to solve the energy. This is a problem I came up with during other simulation. In this other simulation i have two heat exchangers cold one and hot one. I got there work from PdV diagram and work from heat fluxes from heat exchangers (Qh-Qc). I found that they are different by 20% !. So it is kind of strange that I get different amount of work depending on how do I calculate it.

This is why I have tuned off the heat exchangers (in order to get adiabatic case) and got this strange results....

April 4, 2014, 02:32	Moving mesh and thermodynamic issues...	#1
loook New Member Lukasz Join Date: Apr 2012 Posts: 10 Rep Power: 14	Hi, I am working on simulations with moving meshes. I have noticed several strange things using moving mesh: I did simple simulation of a piston which first compress the gas and then moving backward letting gas to expand. There is no heat flux, just motion of a mesh. When I monitor the pressure and total volume I do get positive work!!? How is it possible...? The other thing is heat flux through moving boundary. I have made the "total heat flux report" on each of boundaries and I have noticed relatively large heat flux through my moving boundary (even so it is set to adiabatic) why is that? I did it via Report/Fluxes/TotalHeatTransferRate - does any body know how to monitor this particular flux and write it to file? ( i tried surface integrals... averaging and non of those gives me this strange flux) I will be appreciated for help with those problems...

April 4, 2014, 04:37		#2
Bionico Senior Member Flavio Join Date: Sep 2011 Location: Brescia, Italy Posts: 181 Rep Power: 15	Hi loook, have you tried disabling Energy from Equation menu? Regards __________________ Bionico

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April 4, 2014, 04:58		#3
loook New Member Lukasz Join Date: Apr 2012 Posts: 10 Rep Power: 14	no I did not, because I need to solve the energy. This is a problem I came up with during other simulation. In this other simulation i have two heat exchangers cold one and hot one. I got there work from PdV diagram and work from heat fluxes from heat exchangers (Qh-Qc). I found that they are different by 20% !. So it is kind of strange that I get different amount of work depending on how do I calculate it. This is why I have tuned off the heat exchangers (in order to get adiabatic case) and got this strange results....