Wrong Solution for sensibleEnthalpy
Hello,
I'm using OpenFoamv7. While trying rhoCentralFoam at the shock Tube, I realised that the Solution is different from the analytic Solution. I tracked the misstake to the thermophysicalproperties. When using sensibleEntahlpy for the energy the Soultion seems to be wrong, while using sensibleInternalEnergy results in the correct Solution. Now I'm searching for the reason, because I will have to use sensibleEnthalpy for a individual Solver (the reason I'm using OpenFoam v7). Anyone has an answer to my Problem? |
The difference should likely result from your definition of cv / cp. Aside from that, they should be equal. There are numerical advantages, but the formal definition is identical, so if one has a significantly higher residual that should give it away. If one of them did not converge.
Hence check cv/cp and the residuals. |
I double checked the values for cp and cv and everything seems to be ok....
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Are they the same or different? You might want to use the same value for both
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They are different. Why should using the same value for both result in a correct Solution? They are different by definiton?
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That is the question I am asking....make sure you use the correct values here for the medium, pressure etc you are solving for! With incompressible flow you should have cp=cv...if your medium does not behave like an ideal gas you might want to make sure to double check your thermodynamics. They are only different if some of the energy used to heat up the fluid goes towards thermal expansion...this might not be the case numerically and hence the difference.
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Sorry for the late Reply...
I tried it with cp=cv and I got the right Solution. But I still don't get why. I use a compressible Solver (rhoCentralFoam) with air, so cv and cp can't be the same. Why is the Solution still correct? |
I'm looking at a shock tube with a 20 bar and a 1 bar side so there should be a compression involved...
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