Viscous Flow in Pipes.pdf
Viscous Flow in Pipes.pdf
Viscous Flow in Pipes.pdf
You also want an ePaper? Increase the reach of your titles
YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.
8.3.4 Turbulence Model<strong>in</strong>gTime-averag<strong>in</strong>g approach: need to solve the closureproblem for the Reynolds stresses, such as −ρuυ′ ′, etc.Different methods for Reynolds stress closure:• Algebraic (zero-equation) models—by model<strong>in</strong>g the eddyviscosity or mix<strong>in</strong>g length• One-equation models—solve one additional transport equation• Two-equation models—solve two more additional transportequations, such as k-ε model, k-ω model• Reynolds stress transport models—solve the transport equationfor Reynolds stressesLarge eddy simulations (LES)—explicitly solve for thelarge eddies <strong>in</strong> a calculation and implicitly account for the smalleddies by us<strong>in</strong>g a subgrid-scale model (SGS model).Direct numerical simulations (DNS)—directly solve thetransient 3-D Navier-Stokes equations with very f<strong>in</strong>e grids andtime steps