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aperrone April 12, 2011 17:19

restart after changing boundary conditions
hello everyone!
I'm moving from starcd 4.06.007 to starcd 4.14.008, and I have some problems with the restart after changing the boundary conditions:
in particular I change some boundaries from wall to inlet conditions and then I restart the run. The material within the domain is air, and everything works if at the inlet I employ for instance CH4 or air, while employing H2 I got this strange error message (I use the polynomial treatment for the specific heat ):

*** Error 615: Negative Gamma, please check if Cps are right


If instead I use an air-H2 mixture with low H2 content the run restarts without any problems. I checked the polynomial coefficient and they're right, they're the same employed in the 4.06.07 version with which the same restart was working.

Has anyone experienced this error and knows the reason why it occurs, or could provide me any advice to settle it?

thanks in advance for your help

RobertB April 13, 2011 08:53

Are all your scalar fractions correctly bounded (i.e. between 0 and 1)?

aperrone April 13, 2011 11:06

I think they are, in fact with a H2 scalar fraction inferior to 0.2 the run restarts, instead with higher H2 scalar fraction, for example 0.7 or 1, I got that error message, and this happens only with hydrogen: other scalars work fine.:confused:

RobertB April 13, 2011 11:53

Star uses mass fractions not volume fractions. Hydrogen is light thus a 0.7 mass fraction is more or less a 100% volume fraction.

Perhaps this has something to do with the problem. Perhaps it goes slightly unbounded and that causes a problem, what differencing scheme are you using?

aperrone April 13, 2011 13:11

I also think that the fact that hydrogen is extremely lighter than air deals with the problem, but I need to inject pure hydrogen and I think this means necessarily mass fraction equal to one, otherwise I'd inject a lower mass of hydrogen, a H2-air mixture, are you in agreement, or I'm making a mess?:rolleyes:
I was also thinking that CH4 is lighter than air too, but with a scalar fraction equal to one works well, so do you know how star treats this volume fraction bigger than 100%?
For the scalars I'm using the upwind scheme, please, could you suggest me something more robust?

SMM April 25, 2011 20:53


I think if one wants to change/edit the model then one needs to save the problem file again and then run the solver.

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