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Old   April 2, 2009, 21:37
Exclamation Burning Velocity Model
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George Thomas
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I'm having some trouble using BVM model in CFX. I'm very keen to introduce combustion in my model, and I was trying to employ the BVM model (as it got spark modeling) instead of EDM or FRC. However, I'm not an expert in using CFX, and so I can't find BVM model option in my CFX environment. I do not know why. The only available options are ED, FRC and FRC with ED. I already defined the materials and reactions. I assume they are correct. Could anyone please advice me why I can't use BVM model in my CFX version.
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Old   April 4, 2009, 05:25
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Burning velocity model is coupled with flamelet. So you have to setup reaction object with flamelet library. If you activate this reaction in your mixture material you will be able to use BVM.

It is bit tricky and there is no tutorial showing how it works. However if you take the combustor tutorial as its describbed, you can go from final setup there and simply change it to BVM. In my opinion that's the best way to learn it.
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Old   April 4, 2009, 05:51
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Thank you very much Joey. I'll try the way you suggested. I'll get back to you sooner. As BVM model and Spark Ignition were a new addition to CFX 11.0 they should have given some guidelines on how to use it.
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Old   April 6, 2009, 00:24
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Now I'm able to use the BVM model. Thank you for helping me to sort it out.

However, I'm not able to crack some other mysteries in using BVM model. I hope I can get help from here. Let me say what my problems currently are;

1. When I use the FLL for Methane Air FLL STP and NO PDF, I'm not able to specify the CH4 mass frac at fuel inlet and O2 mass frac at air inlet. Do you know why?

2. Also, what I'm having is a premixed flow through my inlet as the current engine model I'm simulating is for a Gasoline engine. So it's completely premixed flow. However, the BVM model I choose from the Default Domain shows the model name as BVM(Partially Premixed). Do I have any options to use fully premixed flow with spark ignition?

3. Is it possible for me to create FLL with a usual CFX license? Do you know where I can find some information on how to create FLL using CFX-RIF tool?

4. Also, with the above said Methane Air fuel mixture, in the inlet or even in the outlet I can see only 'CO' and 'NO' as the available components. However, in models other than BVM I can even configure CH4 and O2. Could you tell me why?

5. Since it's premixed flow I have both air+fuel mixture flowing through the inlet. Eveventhough, the Mixture I can choose from bvoundary options will allow me to use either 'Oxidiser' or 'Fuel' at a time, and what I want is both at the same time. How can I achieve it?

Please help me with the above queries.
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Old   April 6, 2009, 20:33
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Hi,
I'm having some problem with my IC engine simulation using BVM. I'm getting the following error just at the time of spark ignition.

'ERROR #002100075 has occurred in subroutine SOLVE_RKERNEL.

Message:

The spark region defined by the transition radius is empty, but at least 1 mesh vertex is required to be located inside the transition region. Consider refining the mesh in the region of spark ignition or increase the transition radius.

Domain: Default Domain

Fluid: Methane Air Mixture

An error has occurred in cfx5solve:

The ANSYS CFX solver exited with return code 1. No results file has been created.'

I'm quiet sure that my mesh is fine enough through out the domain. I don't know why I'm getting this error always. Could anyone please help me out. Thank you.
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Old   April 12, 2009, 06:24
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1. Read theory of mixture fraction approach in help, manual or literature or ask your adviser. You will understand.
2. Model for partially premixed is appropriate for premixed also. May save cpu time by using model overwrites for switching off mf and mf var. (works only combined with C-equation not with F-equation)
3. CFX-RIF is an own license.
4. See 1. Possible to solve a transport equation fo NO. You can set boundaries and ini conditions in that case.
5. See 1
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Old   April 13, 2009, 02:06
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Thank You Joey. Lemme try the way you suggested. Will get back to you.

However, I couldn't find much help regarding the Mixture Fraction in CFX help. Could you tell me where it is exactly if I have skipped anything valuable.
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Old   April 17, 2009, 02:32
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I have tried the tutorial you suggested.

However, could you tell me how the combustion/reaction gets activated in the case of PDF Flamelet and EDM models. I can't find them using any energy sources to activate the reaction. In that case how can we activate a reaction/combustion at a particular time in a transient model?
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Old   April 17, 2009, 15:53
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Energy source term will not 'ignite'. These are combustion models not physical reality. Have a look at the transport equations in the help. Analyse the source terms of species equation or reaction progress transport equation. In the latter case the gradient of c is controling the flame propagation. If you have a field of c everywhere zero. What gradient of c do you have when you heat up???????

In case of BVM take the ignition model. In case of EDM use reaction with user defined rate can help.
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