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Simulation of H2/air mixture in a tube

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Old   April 27, 2017, 02:38
Default Simulation of H2/air mixture in a tube
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marharyta
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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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Old   April 27, 2017, 07:22
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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.
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Old   April 27, 2017, 07:33
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Quote:
Originally Posted by ghorrocks View Post
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?
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Old   April 27, 2017, 07:40
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What is your ignition source? A spark? A pilot flame? A high temperature source?
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Old   April 27, 2017, 07:44
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Quote:
Originally Posted by ghorrocks View Post
What is your ignition source? A spark? A pilot flame? A high temperature source?
In real case it is a spark.
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Old   April 27, 2017, 07:59
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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.
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Old   April 27, 2017, 08:09
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Quote:
Originally Posted by ghorrocks View Post
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?
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Old   April 27, 2017, 18:10
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I do not answer CFD questions by PM. Post them on the forum.
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Old   April 27, 2017, 22:38
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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.
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Old   May 11, 2017, 10:01
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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?
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