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-   -   LES turbulence model problem-HELP (http://www.cfd-online.com/Forums/fluent/37605-les-turbulence-model-problem-help.html)

James Willie August 18, 2005 04:33

LES turbulence model problem-HELP
 
Hi All,

I am simulating gas oil and I have a problem with the LES turbulence model. It is working alright but the peak temperature i am getting is 2000K where as for the k-e realizable turbulence model, i am getting a peak temperature of 1800K in the combustor.

Also, the flame shape has changed for the LES. The steady RANS and unsteady RANS cases have a reasonable flame shape. Any explanation for this discrepancy and suggestions of how it can be solved?

For the sub-grid model under LES, i am using Smagorinsky-Lilly.

James

helper August 22, 2005 15:22

Re: LES turbulence model problem-HELP
 
Higher peak temperature with LES is not surprise to me, inasmuch as LES resolves finer scales of motion and temperarure field. Regarding the flame shape, chance is that instantaneous flame shape in LES has lots of wrinkles in it. You've got to compare the time-averaged flame shape with the RANS-based shape.

James Willie August 23, 2005 04:54

Re: LES turbulence model problem-HELP
 
Hi,

Thanks for the help. Will this temperature drop with time? That is what happens after allowing for sufficiently large number of iterations?

Also, how is the time averaged flame temperature obtained? Is it obtained by switching on "Data Sampling for Time Statistics" under "Option" on in the "iterate" panel?

Regards,

James



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