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Introduction to Computational Fluid Dynamics (CFD) - page 16 / 47

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Modeling (Turbulence and free surface models)

Turbulent models:   

DNS: most accurately solve NS equations, but too expensive

          for turbulent flows

RANS: predict mean flow structures, efficient inside BL but excessive

           diffusion in the separated region.

LES: accurate in separation region and unaffordable for resolving BL

DES: RANS inside BL, LES in separated regions.

Free-surface models:   

Surface-tracking method: mesh moving to capture free surface,

 limited to small and medium wave slopes

Single/two phase level-set method: mesh fixed and level-set

  function used to capture the gas/liquid interface, capable of

  studying steep or breaking waves.

Turbulent flows at high Re usually involve both large and small scale

  vortical structures and very thin turbulent boundary layer (BL) near the wall

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