Hello,This post describes the methodology of setting up and running a LES simulation in ANSYS-FLUENT, a very brief description about the meshing and solution procedure is presented here. Compared to RANS, LES simulations require finer grids since it aims in resolving the large scales of turbulent motion thus providing a better insight of the flow physics however LES is a transient simulation and the computation cost of LES much higher than that of RANS, for a detailed review please see:1.) Piomelli, A primer on DNS/LES.2.) Grid-point requirements for large eddy simulation: Chapman's estimates revisited.
Physics of Fluids, 24(1), 2012(also see the original Chapman's paper in the late '70s 78-79)3.) Turbulent flows, Pope (2006).I am not describing the theory of LES here as there are several good books available and I would recommend reading, chapters 1-7 in Pope, and chapter 13 on LES. Chapters 6 and 7 in Pope's book explains about turbulence in free shear turbulent flows (jets, self-similarity) and chapter 7 describes about stable attached turbulent flows (pipes, channels). I would highly recommend reading these as they explain the significance of certain parameters like y+, utau, law of the wall, the regimes in a turbulent velocity profile and so on.The present tutorial is based on pipe flow at Re = 24,580 (experimental data of Toonder & Nieuwstadt, and DNS data of X.
Activate Les 2d Fluent Online
Wu and Moin is available).1.) Create a pipe geometry in ICEM-CFD. Now you can create the parts: inlet, wall etc. And save the mesh and translate it to fluentAlternatively you can set up periodicity in fluent, but sometimes you may end up with errors such as 'segmentation-violation' especially in the case of large meshes.7.) Setting up LES in fluent:I would suggest running a RANS simulation in a similar coarser mesh with pbc in fluent and then interpolating the RANS solution in the present case. After interpolation, you can add fluctuating components to the RANS velocity profile by:/solve/init/init-instantaneous-velOnce done, change the viscous model as Large Eddy Simulation, start with the standard Smagorinsky-Lily model.