• Transport Phenomena Academy: Fluid Mechanics, Heat & Mass Transfer

  Large Eddy Simulation LES is also Small Eddy Simulation SES

  Posted by Aliyar Javadi on October 19, 2024 at 11:43 pm

  Large Eddy Simulation LES is also Small Eddy Simulation SES “However after modeling!”. Then “LE-DNS (Large Eddy Direct Numerical Simulation) or LENM (Large Eddy Not Modeling)” could be a also other descriptive name of LES. As Large Eddies are simulated directly (DNS approach) without turbulence modeling. We could call it also “LES-SEMS (Small Eddy Modeling then Simulation)”. The names and terminology are really important to take correct imagination and keep in mind properly.

  Re-View on Large Eddy Simulation (LES):

  In Large Eddy Simulation (LES), the large eddies (or larger turbulent structures) are resolved directly using computational methods, meaning that the simulation captures their dynamics with relatively high fidelity. These large eddies are important because they contain most of the turbulent kinetic energy and significantly influence the momentum and energy transport.
  However, the smaller eddies, which are less computationally feasible to resolve directly due to their finer spatial and temporal scales, and need of very fine mesh and computational cost, are modeled and then simulated.

  This is where a subgrid-scale (SGS) model comes into play to approximate the effects of these smaller eddies on the resolved larger structures. This portion of the LES process is indeed a form of “small eddies turbulence modeling.” The goal is to balance the computational expense by only directly simulating the scales that matter most for the bulk flow behavior, while using models to approximate the effects of smaller, more universally behaving structures towards dissipations.

  This hybrid approach is one of the defining features that makes LES more accurate than Reynolds-Averaged Navier-Stokes (RANS) but more computationally manageable than Direct Numerical Simulation (DNS).

  Numerical Solution of the SGS Model:
  However, we should note that, once the SGS model is defined (e.g., Smagorinsky, Dynamic Smagorinsky, WALE), its contribution is included in the discretized Navier-Stokes equations that are solved numerically on a computational grid. This is also a kind of CFD simulation, however not DNS. Then as we have RANS CFD simulation, we can say in LES approach, small eddies also are simulated finally in LES, however after modeling.

  This means that, even though the SGS model involves approximations, it still requires numerical computation to integrate its effects with the resolved flow. This process is part of the numerical simulation of the entire flow field, combining both the large eddies (directly resolved) and the small eddies (modeled through SGS).

  Next Turbulence Course: https://lnkd.in/ewgQD3uz (Starting next week)

  Reference: WAC Transport Phenomena Academy (https://lnkd.in/ePErpz8R , World-Academies.Com (Dresden, Germany).

  Video: https://lnkd.in/egedGuSF

  #Fluiddynamic #turbulence #turbulentflows #mechanicalengineering #aerospace

  #processengineering #chemicalengineering #CFD #OpenFOAM #DNA #RANS #LES

  Aliyar Javadi replied 1 month ago 1 Member · 0 Replies
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