In this chapter, several physical situations are examined: fluid flows (1) with secondary swirl, (2) in a pipe bend, (3) in round pipes, (4) in a rectangular duct, and finally (5) through perforated plates. In each of these cases, validation was performed using accurate and complete experimental results available in the published literature to be compared with appropriate numerical simulations. Different quantities are used for validation metric depending on the availability of experimental data, i.e., comparing velocity profiles, local Nusselt numbers, and pressure drop. Several popular turbulence models, κ − ɛ RNG κ − ɛ κ − ω SST κ − ω and WALE LES were investigated. The first two cases, (1) and (2), utilized available velocity and turbulence profiles at the inlet of the solution domain. From Case (1), the SST κ − ω turbulence model clearly was the preferred choice because of the good agreement with experimental data and the shorter CPU time required as compared to the LES model. The remaining cases (2)–(5) were primarily investigated with the SST κ − ω turbulence model. Overall, the SST κ − ω turbulence model performed very well compared to the available experimental data for all of the cases investigated here.