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[FAQ]

Some general guidelines on choosing the turbulence modeling options available in Fluent are as follows: Spalart- Allmaras: Economical for large meshes. Performs poorly for 3D flows, free shear flows, flows with strong separation. Suitable for mildly complex (quasi-2D) external/internal flows and b.l. flows under pressure gradient (e.g. airfoils, wings, airplane fuselage, missiles, ship hulls). Standard k-epsilon: Robust. Widely used despite the known limitations of the model. Performs poorly for complex flows involving severe separation, strong stream line curvature. Suitable for initial iterations, initial screening of alternative designs, and parametric studies. RNG k- epsilon: Suitable for complex shear flows involving rapid strain, moderate swirl, vortices, and locally transitional flows (e.g., b.l. separation, massive separation and vortex-shedding behind bluff bodies, stall in wide-angle diffusers, room ventilation) Realizable k- epsilon: Offers largely the same benefits and has similar applications as RNG. Possibly more accurate and easier to converge than RNG. Standard k-omega: Superior performance for wall-bounded b.l., free shear, and low Re flows. Suitable for complex boundary layer flows under adverse pressure gradient and separation (external aerodynamics and turbomachinery). Can be used for transitional flows (though tends to predict early transition). Separation is typically predicted to be excessive and early. SST k-omega: Similar benefits as SKO. Dependency on wall distance makes this less suitable for free shear flows. RSM: Physically the soundest RANS model. Avoids isotropic eddy viscosity assumption. More CPU time and memory required. Tougher to converge due to close coupling of equations. Suitable for complex 3D flows with strong streamline curvature, strong swirl/rotation (e.g. curved duct, rotating flow passages, swirl combustors with very large inlet swirl, cyclones).