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Inflow construction for LES

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Old   June 13, 2015, 19:13
Default Inflow construction for LES
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Julio Mendez
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Dear colleagues,

I have read about construction of inflow conditions for LES. Basically there are two approaches, sythesised and precursor simulation. The former is ver straight forward but it seems that it lacks of soundness becuase it usus some harmonic functions and statistics to mimic the energy spectrum of a particular flow.
The precursor simulation seems to be more used but, I am still trying to understand something that is not "clicking" in my mind.
On the precursor simulation, periodic boundary conditios is used. Usually on both direction on the horizontal plane. However, my main questions is related to the streamwise periodic boundary condition.
From a physical point of view, the turbulence structure is defined upstream (inlet) and under these assumption, these turbulence structure is advected downstream. Finally, at the outlet the turbulent profile (stress, statistics etc) will be very different from the inlet definition. However, defining a periodic boundary conditions at the outlet, it forces to have the same flux as the inlet (even the turbulent flux). As the turbulent layer develops the turbulent stress also changes and impossing the flux at the outlet is almost killing the real physics of the phenomena.
Also according to tabor et al. 2010. They claimed that using a precursor simulations allows to use different Re number between the precursor simulation and the real simulation. The only restrictions is the cross section of the area. But, we know that Re number defines the length and time scales, and also the turbulent structure of the flow...
Is there something I am overlooking ????

thanks in advanced!!

Last edited by juliom; June 13, 2015 at 19:19. Reason: I forgot to mentioned something!!
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