restart after changing boundary conditions

aperrone · April 12, 2011, 17:19

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

RUN STOPPED !!!

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
Antonella

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.

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?

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

Hi,

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

April 12, 2011, 17:19	restart after changing boundary conditions	#1
aperrone New Member Antonella Join Date: Apr 2011 Posts: 3 Rep Power: 15	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 RUN STOPPED !!! 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 Antonella

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Boundary Conditions	Thomas P. Abraham	Main CFD Forum	20	July 7, 2013 05:05
RPM in Wind Turbine	Pankaj	CFX	9	November 23, 2009 04:05
CFX doesn't continue calculation...	mactech001	CFX	6	November 15, 2009 21:25
Water vapour condensation in CFX-5.7.1	hdj	CFX	1	November 27, 2005 07:15
Convective Heat Transfer - Heat Exchanger	Mark	CFX	6	November 15, 2004 15:55

April 13, 2011, 08:53		#2
RobertB Senior Member Robert Join Date: Jun 2010 Posts: 117 Rep Power: 16	Are all your scalar fractions correctly bounded (i.e. between 0 and 1)?

April 13, 2011, 11:06		#3
aperrone New Member Antonella Join Date: Apr 2011 Posts: 3 Rep Power: 15	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.

April 13, 2011, 11:53		#4
RobertB Senior Member Robert Join Date: Jun 2010 Posts: 117 Rep Power: 16	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?

April 13, 2011, 13:11		#5
aperrone New Member Antonella Join Date: Apr 2011 Posts: 3 Rep Power: 15	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? 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?

April 25, 2011, 20:53		#6
SMM New Member Syed Murtuza Mehdi Join Date: Apr 2011 Posts: 19 Rep Power: 14	Hi, I think if one wants to change/edit the model then one needs to save the problem file again and then run the solver.