Overview of Computational Approache to Introductory FLUENT Notes Fluent User Services cente LUENT v6. 3 December 2006 wwfluentusers. com UENT Reynolds-Averaged Navier-Stokes(RANS) models Solve ensemble-averaged (or time-averaged) Navier-Stokes equations All turbulent length scales are modeled in rans The most widely used approach for calculating industrial flows Large Eddy Simulation (LES Solves the spatially averaged N-S equations. Large eddies are directly resolved, but eddies smaller than the mesh are modeled Less expensive than dns, but the amount of computational resources and efforts are still too large for most practical applications Direct Numerical Simulation (DNS Theoretically, all turbulent flows can be simulated by numerically solving the full Navier-Stokes equations Resolves the whole spectrum of scales. No modeling is required But the cost is too prohibitive! Not practical for industrial flows-DNS is not available in Fluent There is not yet a single, practical turbulence model that can reliably predict all turbulent flows with sufficient accuracy C 2006 ANSYS. nc All ANSYS, Inc. Proprietar© 2006 ANSYS, Inc. All rights reserved. 6-5 ANSYS, Inc. Proprietary Fluent User Services Center www.fluentusers.com Introductory FLUENT Notes FLUENT v6.3 December 2006 Overview of Computational Approaches ◆ Reynolds-Averaged Navier-Stokes (RANS) models ⚫ Solve ensemble-averaged (or time-averaged) Navier-Stokes equations ⚫ All turbulent length scales are modeled in RANS. ⚫ The most widely used approach for calculating industrial flows. ◆ Large Eddy Simulation (LES) ⚫ Solves the spatially averaged N-S equations. Large eddies are directly resolved, but eddies smaller than the mesh are modeled. ⚫ Less expensive than DNS, but the amount of computational resources and efforts are still too large for most practical applications. ◆ Direct Numerical Simulation (DNS) ⚫ Theoretically, all turbulent flows can be simulated by numerically solving the full Navier-Stokes equations. ⚫ Resolves the whole spectrum of scales. No modeling is required. ⚫ But the cost is too prohibitive! Not practical for industrial flows - DNS is not available in Fluent. ◆ There is not yet a single, practical turbulence model that can reliably predict all turbulent flows with sufficient accuracy