Introductory FLUENT Notes Fluent User Services cente ANSYS LUENT v6. 3 December 2006 wwfluentusers. com FLUENT The k-e Turbulence models Standard k-8(SKE)model The most widely-used engineering turbulence model for industrial applications Robust and reasonably accurate Contains submodels for compressibility, buoyancy, combustion, etc Limitations u The a equation contains a term which cannot be calculated at the wall. Therefore wall functions must be used Generally performs poorly for flows with strong separation, large streamline curvature,and large pressure gradient Renormalization group (rngak-8 model Constants in the k-e equations are derived using renormalization group theory Contains the following submodels Differential viscosity model to account for low Re effects Analytically derived algebraic formula for turbulent Prandtl /Schmidt number Swirl modification Performs better than SKe for more complex shear flows, and flows with high strain rates swirl. and separation C 2006 ANSYS. nc All ANSYS, Inc. Proprietar© 2006 ANSYS, Inc. All rights reserved. 6-11 ANSYS, Inc. Proprietary Fluent User Services Center www.fluentusers.com Introductory FLUENT Notes FLUENT v6.3 December 2006 The k–ε Turbulence Models ◆ Standard k–ε (SKE) model ⚫ The most widely-used engineering turbulence model for industrial applications ⚫ Robust and reasonably accurate ⚫ Contains submodels for compressibility, buoyancy, combustion, etc. ⚫ Limitations ◼ The ε equation contains a term which cannot be calculated at the wall. Therefore, wall functions must be used. ◼ Generally performs poorly for flows with strong separation, large streamline curvature, and large pressure gradient. ◆ Renormalization group (RNG) k–ε model ⚫ Constants in the k–ε equations are derived using renormalization group theory. ⚫ Contains the following submodels ◼ Differential viscosity model to account for low Re effects ◼ Analytically derived algebraic formula for turbulent Prandtl / Schmidt number ◼ Swirl modification ⚫ Performs better than SKE for more complex shear flows, and flows with high strain rates, swirl, and separation