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

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.

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.

Regards

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)