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LES model (oneEqEddy), air entrainment predictions

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Old   November 4, 2010, 16:02
Default LES model (oneEqEddy), air entrainment predictions
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N. A.
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Hello Foamers,

So I am trying to model a coal+O2 jet along with an H2O annular jet in a cylidnerical geometry using coalChemistryFoam. I find that if I use LES model, the mean velocity field is over predicted in the domain, i.e. the jet does not seem to sexpand and entrain the surrounding air. in LES I see that there is a high velocity at the outlet boundary. ? --Dont understand why this happends..Is this a boudnary condition issue

On the other hand the RANS model predicts that the velocity decays because of air entrainment and mixing.

the inlet boundary condition for velocity is fixed value and turbulent inlet. the outlet velocity boundary condition is inletOutlet. for pressure I am using total pressure value for both inlet and outlets.

Attached are the plots comapring velocit field predicted using RANS and LES. LES does not rpedict decay of jet velocity as usually the trend with jets, but RANS is able to do that.

Any inputs as to why LES is nto able to match the trends and what can be done, will be very helpful.

Thanks,
Nir
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File Type: jpg LES_GASIFIER.jpg (33.5 KB, 70 views)
File Type: jpg RANS_GASIFIER.jpg (30.9 KB, 54 views)
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Old   November 7, 2010, 13:17
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Eugene de Villiers
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You need to use a mapped inlet for U and k to obtain the correct inlet turbulence and thus spreading rate. See tutorials/incompressible/pisoFoam/les/pitzDailyMapped
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