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What is reference temperature?

Posted Nov 12, 2019, 12:43 p.m. EST General, Computational Fluid Dynamics (CFD), Structural Mechanics 1 Reply

Aman Zahar
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dear everybody,

may i know the function of reference temperature? i've read somewhere that it is only imporatant for solid mechanics problem, is this true? does it play an important role for fluid flow and heat transfer coupling problem? I need to be sure. thank you

1 Reply Last Post Nov 13, 2019, 2:21 a.m. EST
Henrik Sönnerlind COMSOL Employee

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Posted: 5 years ago Nov 13, 2019, 2:21 a.m. EST

Hi Aman,

The reference temperature serves two purposes. The first one is the more obvious: it is the temperature at which there is no thermal strain in a solid. The thermal strain is computed as

The other purpose, also related to solid mechanics, is that the reference temperature at which the mass density is evaluated (if it is temperature dependent). For a physics interface which is formulated on the material frame, mass conservation dictates that the density must be constant during the simulation. Volume changes due to thermal expansion are taken care of only through the thermal strain. Any physics interface which is formulated on the material frame must have this interpretation of mass density.

The latter case can be thought of as "the reference temperature is the temperature at which the geometry is exactly the one I modeled".

The opposite case you can find in for example fluid dynamics where a fixed control volume is studied ('Eulerian formulation'). In this case, the mass of the fluid inside the control volume can change, and a truly temperature dependent density is appropriate. The reference temperature is irrelevant here.

Regards,
Henrik

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Henrik Sönnerlind
COMSOL
Hi Aman, The reference temperature serves two purposes. The first one is the more obvious: it is the temperature at which there is no thermal strain in a solid. The thermal strain is computed as \epsilon_{th} = \alpha (T-T_{ref}) The other purpose, also related to solid mechanics, is that the reference temperature at which the mass density is evaluated (if it is temperature dependent). For a physics interface which is formulated on the *material frame*, mass conservation dictates that the density must be constant during the simulation. Volume changes due to thermal expansion are taken care of only through the thermal strain. Any physics interface which is formulated on the material frame must have this interpretation of mass density. The latter case can be thought of as "the reference temperature is the temperature at which the geometry is exactly the one I modeled". The opposite case you can find in for example fluid dynamics where a fixed control volume is studied ('Eulerian formulation'). In this case, the mass of the fluid inside the control volume can change, and a truly temperature dependent density is appropriate. The reference temperature is irrelevant here. Regards, Henrik

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