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Old   April 30, 2008, 20:25
Default Pls help Combustion Gurus
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I am working on steady state premixed turbulent combustion problem of methane and air. The system is 36 inch long consists of a inlet pipe, swirler and a combustion zone.

I just followed the tutorial,Can you let me know how to calculate the turbulence intensity, backflow turbulence intensity and backflow hydraulic diameter.

I dont know the difference betn Eddy dissipation and Finite rate chemetry method for turbuent. I just used Eddy dissipation.Also pls let me know what other things I need to calculate coz I took all the properties of mixture of methane and air by default.Also I am new to combustion, so I dont know what else I should calculate.

I did the simulation for 2000 iteration but it does not converge shall I continue for more iteration.

Thank you very much,

Waiting for your reply
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Old   May 2, 2008, 08:03
Default Re: Pls help Combustion Gurus
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If you look in the Fluent documentation there's an equation to calculate the turbulence intensity. And the hydraulic diameter is the diameter of the pipe, and backflow means the turbulence intensity that you expect at the outlet, incase of reversed flow, which will be large. Or you can use an outflow which extrapolates the downstream values from the upstream ones.

For turbuelent flows you should use the eddy dissipation, but if the system is premixed you should use the finite rate/eddy dissipation model. But I advise you to use the non-premixed/premixed/or partially premixed models instead. Although None of the considered models take into account turbulent quenching which may or may not cause a preoblem for your case.

It depends on how big your grid is for the iterations. You should first calculate a solution without combustion, then implement the combustion models. It also depends if the solution is stable or not: If it's gradually converging smoothly then let it have as many as it needs, if the residuals are going up and down then you need to improve the quality of your grid by cutting out sharp angles as much as possible.

Hope this helps Phil
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Old   May 12, 2008, 12:07
Default Re: Pls help Combustion Gurus
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Fluent's website has a power point presentation called:

Gaseous Combustion, Best Practices or something...


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