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-   -   Adiabatic compression (http://www.cfd-online.com/Forums/cd-adapco/56981-adiabatic-compression.html)

Erik January 29, 2009 15:24

Adiabatic compression
 
Hi all, I'm simulating a compressing piston using a moving mesh of a 1/7th slice of the cylinder. When I perform a simulation where the in-cylinder air is compressed adiabatically, the pressure at TDC is too high, compared to the pressure calculated using the ideal gas law. When I look at the temperature, it is calculated very accurately and the volume during the compression stroke is exact the same as in the ideal gas law calculation and the mass inside remains constant. So that's very strange, as pressure is determined by temperature, volume, mass and cp.

The density is calculated using the ideal f(T,P) function, the cp of the air is a polynomial from the chemkin database, the walls of the slice are cyclic boundaries, the piston and head are adiabatic walls, the solver timestep is 0.1 dCA. Is there someone who has a possible explanation, because I think I've tried everything right now (changing boundaries, scalars, heat capacity etc..) Thanks!

Pauli January 29, 2009 18:17

Re: Adiabatic compression
 
"the cp of the air is a polynomial from the chemkin database"

The chemkin database does not have a material "air". You are likely using the polynomial for N2.

Erik January 30, 2009 03:31

Re: Adiabatic compression
 
That's true, I've used the polynomial for N2


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