Turbulent flow in a diffuser with swirl occurs in many commonly used fluid mechanical devices.eg, diffusers located downstream of a gas turbine, and in certain types of combustion chambers. Diffusers are widely used for converting kinetic energy to pressure, and a reliable prediction method of such flows with the required flow conditions would lead to the design of fluid machinery with improved efficiency. As a first step, turbulent swirling flow through a 12° included angle conical diffuser for a swirl parameter, m = 0.18 was numerically investigated using various turbulence models like standard k-ε, RNG-based k-ε, shear-stress transport (SST) k-ω, and Reynolds stress model (RSM). Though the comparison between the experimental and the predicted mean velocity profile by RSM is superior to that by RNG k-ε and SST models, the latter two models give closer comparison with the experimental pressure distribution. Subsequently, computation of flow inside a complex duct involving axisymmetric annular diffuser, transition from rectangular to circular cross section, and exit pipe have been carried out using RNG k-ε and SST k-ω models. The comparison of computed and experimental results indicates that the SST k-ω model gives predictions with reasonable accuracy. © 2006, DESIDOC.