R used in thermodynamicproperties

srinath · June 13, 2008, 10:33

Hi

I find that R is set to .714286J/(KgK), in most of the examples.
This does not correspond to specific gas constant of air. So is foam assuming some strange gas for the examples or am i missing something?

Univeral gas constant = 8.314J/(mol K)
Mol wt of air =29gm/mol
Therefore specific gas constant = 8.314/.029 = 287 J/(Kg K)--Also confirmed by wikipedia

Am i missing something trivial here?

Could someone please clear this, as i am trying to benchmark the solvers?

Regards
Srinath

ash · June 13, 2008, 11:26

Can you please list out the tutorials.
But in sonicFoam tutorial its given correctly only

srinath · June 13, 2008, 12:29

The value of R, i find in

/tutorial/sonicFoam/forwardstep/constant/thermodynamicProperties is
as follows

R [0 2 -2 -1 0 0 0] 0.714286;

But i do notice that it is set to 287 in the shockTube directory.--Strange

Regards
Srinath

ngj · June 16, 2008, 03:47

Hi

If you look in the Programmers Guide pp 61, you will find that R is set, such that the speed of sound in air is 1 m/s.

Best regards,

Niels

srinath · June 16, 2008, 06:41

Thanks Niels

I also find in the Programmers guide a reference to thermal conductivity kappa.
But nowhere in the code for sonicFoam is kappa even used. It is also not mentioned in thermodynamicProperties in ver-1.4.1

Is this a minor oversight, which can be fixed trivially, by changing mu in the energy equation to kappa?

Regards
Srinath

June 13, 2008, 10:33	Hi I find that R is set to	#1
srinath Member srinath Join Date: Mar 2009 Location: Champaign, USA Posts: 91 Rep Power: 17	Hi I find that R is set to .714286J/(KgK), in most of the examples. This does not correspond to specific gas constant of air. So is foam assuming some strange gas for the examples or am i missing something? Univeral gas constant = 8.314J/(mol K) Mol wt of air =29gm/mol Therefore specific gas constant = 8.314/.029 = 287 J/(Kg K)--Also confirmed by wikipedia Am i missing something trivial here? Could someone please clear this, as i am trying to benchmark the solvers? Regards Srinath

June 13, 2008, 11:26	Can you please list out the tu	#2
ash New Member Arun Shourie Join Date: Mar 2009 Location: Singapore Posts: 12 Rep Power: 17	Can you please list out the tutorials. But in sonicFoam tutorial its given correctly only

June 13, 2008, 12:29	The value of R, i find in	#3
srinath Member srinath Join Date: Mar 2009 Location: Champaign, USA Posts: 91 Rep Power: 17	The value of R, i find in /tutorial/sonicFoam/forwardstep/constant/thermodynamicProperties is as follows R [0 2 -2 -1 0 0 0] 0.714286; But i do notice that it is set to 287 in the shockTube directory.--Strange Regards Srinath

June 16, 2008, 03:47	Hi If you look in the Progr	#4
ngj Senior Member Niels Gjoel Jacobsen Join Date: Mar 2009 Location: Copenhagen, Denmark Posts: 1,900 Rep Power: 37	Hi If you look in the Programmers Guide pp 61, you will find that R is set, such that the speed of sound in air is 1 m/s. Best regards, Niels __________________ Please note that I do not use the Friend-feature, so do not be offended, if I do not accept a request.

June 16, 2008, 06:41	Thanks Niels I also find in	#5
srinath Member srinath Join Date: Mar 2009 Location: Champaign, USA Posts: 91 Rep Power: 17	Thanks Niels I also find in the Programmers guide a reference to thermal conductivity kappa. But nowhere in the code for sonicFoam is kappa even used. It is also not mentioned in thermodynamicProperties in ver-1.4.1 Is this a minor oversight, which can be fixed trivially, by changing mu in the energy equation to kappa? Regards Srinath