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Jonathan Lemay October 30, 2007 21:00

Mixture fraction for combustion problem
Hi everyone

I was wondering if anybody could help me with my problem of getting the mixture fraction available on the result file on my simulation. I am simulating a case in which I am burning Methane and air. I established a material call Methane Air Mixture in which includes CH4, O2 and N2 as pure substance. I simply adjust the mass fraction with the respect of my boundaries conditions for a non premixed burner.

Is there an option I have to select to get the mixture fraction as a variable available in the results file. I tried reactive and non reactive flow but I am only getting the mass fraction of my species and not the overall mass fraction?

Could somebody give me a tip? Best Regard

joey2007 November 1, 2007 16:22

Re: Mixture fraction for combustion problem
Hi, there is more than one way. You can just rerun your case with Burning velocity model. With this approach mixture fraction is a primitive variable. Solver setups it automatically.

Alternatively: you can calculate using CEL in CFX post.

Jonathan Lemay November 4, 2007 20:55

Re: Mixture fraction for combustion problem
Hi Joey

Thanks for your tips I will try this way. What do you mean with the Burning velocity model? Is it a combustion model available in CFX-Pre? Is it a turbulente model?

Finally I found out a way to get what I was looking for. I was running a non-reacting case in which I wanted to estimate the mixing field of CH4 surrounding by air. It work out for the mixture fraction choosing a right combustion model (containing good librairies of flamelet) and setting it to ISOTHERMAL (I chose 300K) in the field of heat transfer. It finally work this way.


joey2007 November 5, 2007 15:57

Re: Mixture fraction for combustion problem
You are right. I am sorry that I missed. You have to use one the combustion models based on the mixture fraction approach. In the case of a diffusion flame this is Laminar Flamelet model. In the (partially) premixed cases this is the Burning velocity model. You can chose both models when you set up a corresponding reaction. (In the library they are termed fll)

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