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-   -   varghese@itw.uni-stuttgart.de (http://www.cfd-online.com/Forums/fluent/31997-varghese-itw-uni-stuttgart-de.html)

varghese August 19, 2003 09:41

varghese@itw.uni-stuttgart.de
 
Dear all!

I have a strange observation in Fluent after initialization of the domain.

I initialized the domain with a constant temperature and some finite value for z-velocity and turbulent parameters. To my surprise I observe at some fluid domain the internal energy assuming negative values.

By definition internal energy is a product of the Specific heat and the Temperature, which is not expected to be negative.

What shall then be the reason for this strange observation. Has somebody similar observations?

Greetings Varghese

mystic_cfd August 20, 2003 05:43

Re: varghese@itw.uni-stuttgart.de
 
Hi Varghese

I would first check eq.(11.2-5) in the Fluent manual. The definition of the enthalpy includes a reference temperature of 298.15K. So you get a negative value if the patched initial temperature is below this value. There is nothing wrong in this case. If you are already aware of this, then you might have a more serious problem?

bye4now


varghese August 21, 2003 04:23

Re: varghese@itw.uni-stuttgart.de
 
I am aware of that fact, dear mystic_cfd.

But I initialize the entire domain with the same temperature everywhere. Hence I donot expect negative values originating from the existence of some reference temperature.

But the domain has two fluids of different specific heats. I wonder whether there exists also another reference specific heat which makes the internal energy of the lower specific heat domain negative.

Greetings Varghese


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