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Old   August 2, 2001, 08:21
Default Need Help for LES
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Has anybody tried to use Large Eddy Simulation (LES) in PHOENICS? Could anyone tell me how to introduce the velocity fluctuations in the inlets and how to show turbulence intensities when using LES? The default attribute for inflow seems to be laminar. So what I should do if I want to simulate a turbulent-boundary-layer approaching flow in PHOENICS? Please help. Thanks.
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Old   August 7, 2001, 05:14
Default Re: Need Help for LES
Mike Malin
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PHOENICS merely provides the vehicle for performing the 3d time-dependent simulation with the Smagorinsky sub-grid scale model. GROUND coding would be needed to use an alternative sub-grid-scale model, to introduce velocity fluctuations at inlets (in Group 13 of GROUND), and to take statistics such as the turbulent intensities. The user must also decide on the time stepping, typically time steps should be no larger than 1/50th of the LET (large-eddy turnover time.

I have seem many proposals in the literature, and I think you need do a little research as to the best means of superimposing "random" inlet fluctuations on the incoming velocities. There may be information in the following references: (a)P.Voke & S.Gao, 'LES of plane impinging jets', Int.J.Num.Methods in Engng', Vol.8, p489, (1995); (b) Y.Dai et al, 'LES of plane turbulent jet flow using a new outflow velocity boundary condition', JSME Int.J., Series B, Vol.37, No.2, p242, (1994); and (c) G.Hoffmann & C.Benocci, 'Numerical simulation of spatially-developing planar jets, 26-1, 74th Fluid Dynamics Symp., Chania, Crete, (1994).

The statistics may be carried out in Group 19 of GROUND by performing the usual time-averaging procedure so as to determine mean velocities, normal stresses, shearing stresses, etc.

I suggest that you look at this reference: M.Ciofalo, 'LES; A critical survey of models and applications', p321, Advances & Heat Transfer, Vol.25, Academnic Press, (1994). In there you will also find his PhD thesis referenced, and that thesis provides very useful information on making practical LES simulations with the CFD Finite-Volume Method.
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