Simulation of H2/air mixture in a tube

Faust1 · April 27, 2017, 02:38

Hi!

Now I am working on a simulation of H2/air mixture in a tube. I read that suitable for this task is a model Finite rate chemistry. Ignition model using the expression:
x1=0[m]
y1=0[m]
z1=0[m]
T1=1000[K]*(if(abs(Z-z1)<0.01[m],1,0)*if(abs(Y-y1)<0.01[m],1,0)*if(abs(X-x1)<0.01[m],1,0))+273[K]*(1-if(abs(Z-z1)<0.01[m],1,0)*if(abs(Y-y1)<0.01[m],1,0)*if(abs(X-x1)<0.01[m],1,0)),
and use this temperature in domaine initialization.
But the results of calculations are non-physical. Maybe, somebodycould send me a similar case for reference?
I am a freshhand. Any suggestions will be appreciated! Thanks!

ghorrocks · April 27, 2017, 07:22

If the results are non-physical that suggests your ignition model is non-physical. I would have thought a constant fixed temperature of 1000K in a small region which then jumps to a constant temperature of 273K would be a pretty poor model of an actual ignition source.

Faust1 · April 27, 2017, 07:33

Quote:

Originally Posted by ghorrocks

If the results are non-physical that suggests your ignition model is non-physical. I would have thought a constant fixed temperature of 1000K in a small region which then jumps to a constant temperature of 273K would be a pretty poor model of an actual ignition source.

How then to simulate the stoker of ignition? Do you have some recommendations?

ghorrocks · April 27, 2017, 07:40

What is your ignition source? A spark? A pilot flame? A high temperature source?

Faust1 · April 27, 2017, 07:44

Quote:

Originally Posted by ghorrocks

What is your ignition source? A spark? A pilot flame? A high temperature source?

In real case it is a spark.

ghorrocks · April 27, 2017, 07:59

Sparks are usually a known amount of energy in a very small volume. So use a small source region and apply the spark energy as a heat source (probably as Watts).

Note that you often have to give numerical models of combustion a bit more of a kick to get them started than you do real combustion. So you might need to give it a bit of extra energy to start if off.

Faust1 · April 27, 2017, 08:09

Quote:

Originally Posted by ghorrocks

Sparks are usually a known amount of energy in a very small volume. So use a small source region and apply the spark energy as a heat source (probably as Watts).

Note that you often have to give numerical models of combustion a bit more of a kick to get them started than you do real combustion. So you might need to give it a bit of extra energy to start if off.

Thank you, I will try to do this using an energy source.
If I will have some question, can I write you directly?

ghorrocks · April 27, 2017, 18:10

I do not answer CFD questions by PM. Post them on the forum.

Opaque · April 27, 2017, 22:38

Why are the results non-physical ? The gases do not react ? or the maximum temperature is higher than expected ?

If the latter one, you should be able to compute the adiabatic temperature for a mixture of H2, N2, O2 to verify the maximum temperature. Be careful with reading reported adiabatic temperatures w/o inspecting which species are present in the mixture.

Any additional information might help those in the forum to help you.

Faust1 · May 11, 2017, 10:01

Now I understand that the use of models Finite rate chemistry not allow me to evaluate the rate of spread of flame. So, for my task is only acceptable model of Burning Velocity Model (BVM).
In the setting of the model BVM are correlations Zimont, Peters and Mueller. What correlation must be used in my task?

April 27, 2017, 02:38	Simulation of H2/air mixture in a tube	#1
Faust1 New Member marharyta Join Date: Apr 2017 Posts: 5 Rep Power: 8	Hi! Now I am working on a simulation of H2/air mixture in a tube. I read that suitable for this task is a model Finite rate chemistry. Ignition model using the expression: x1=0[m] y1=0[m] z1=0[m] T1=1000[K](if(abs(Z-z1)<0.01[m],1,0)if(abs(Y-y1)<0.01[m],1,0)if(abs(X-x1)<0.01[m],1,0))+273[K](1-if(abs(Z-z1)<0.01[m],1,0)if(abs(Y-y1)<0.01[m],1,0)if(abs(X-x1)<0.01[m],1,0)), and use this temperature in domaine initialization. But the results of calculations are non-physical. Maybe, somebodycould send me a similar case for reference? I am a freshhand. Any suggestions will be appreciated! Thanks!

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April 27, 2017, 07:22		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	If the results are non-physical that suggests your ignition model is non-physical. I would have thought a constant fixed temperature of 1000K in a small region which then jumps to a constant temperature of 273K would be a pretty poor model of an actual ignition source.

April 27, 2017, 07:40		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	What is your ignition source? A spark? A pilot flame? A high temperature source?

April 27, 2017, 07:59		#6
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	Sparks are usually a known amount of energy in a very small volume. So use a small source region and apply the spark energy as a heat source (probably as Watts). Note that you often have to give numerical models of combustion a bit more of a kick to get them started than you do real combustion. So you might need to give it a bit of extra energy to start if off.

April 27, 2017, 18:10		#8
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	I do not answer CFD questions by PM. Post them on the forum.

April 27, 2017, 22:38		#9
Opaque Senior Member Join Date: Jun 2009 Posts: 1,804 Rep Power: 32	Why are the results non-physical ? The gases do not react ? or the maximum temperature is higher than expected ? If the latter one, you should be able to compute the adiabatic temperature for a mixture of H2, N2, O2 to verify the maximum temperature. Be careful with reading reported adiabatic temperatures w/o inspecting which species are present in the mixture. Any additional information might help those in the forum to help you.

May 11, 2017, 10:01		#10
Faust1 New Member marharyta Join Date: Apr 2017 Posts: 5 Rep Power: 8	Now I understand that the use of models Finite rate chemistry not allow me to evaluate the rate of spread of flame. So, for my task is only acceptable model of Burning Velocity Model (BVM). In the setting of the model BVM are correlations Zimont, Peters and Mueller. What correlation must be used in my task?