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-   -   Inviscid flow calculator, Entropy rise?!! (http://www.cfd-online.com/Forums/main/5968-inviscid-flow-calculator-entropy-rise.html)

MJK April 8, 2003 11:21

Inviscid flow calculator, Entropy rise?!!
 
Hello there,

I was wondering how is possible that inviscid flow calculators (Euler Solvers) can predict entropy rise correctly?

Noting that viscoity and thermal conductivity are the only means which could produce loss and they are taken to be zero in inviscid flow, then how is it possible to have irreversibilities due to shocks when inviscid model is used?

Thanks

MJK

Pao April 8, 2003 11:42

Re: Inviscid flow calculator, Entropy rise?!!
 
you have artificial viscosity in Euler code. Have you noticed total pressure loss at lot at low Mach in Euler code when there is reverse flow?

MJK April 8, 2003 11:51

Re: Inviscid flow calculator, Entropy rise?!!
 
Thanks Pao,

Right. For central schemes like Jameson's you set artifitial viscosity to a value giving you right answer.

But smarter scheme like upwind usually need no setting for artifitial diffusion and they still give a correct answer! So how smart should be these schemes with no tuning, they automatically feed in a right amount of artifitial diffusion to predict entropy rise correctly.

Thanks again

MJK

Kevin April 9, 2003 03:36

Re: Inviscid flow calculator, Entropy rise?!!
 
The dissipation in the inviscid schemes is needed for stability purpose.

The entropy rise (jump) accros a shock is generated by the discontinuity of the computed value : Euler equations fulfil the Rankine-Hugoniot jump relations and so give an entropy rise.

I don't know if it's right or complete but maybe it will help you.

Regards,

Kevin


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