Results from three-dimensional (3-D) simulations of turbulent forced convection adjacent to backward-facing step in a rectangular duct using a k-epsilon-zeta-f turbulence model are reported. This turbulence model is numerically robust near the wall, and it has been shown to predict turbulent heat transfer in separated and wall-bounded flows better than commonly used two-equation turbulence models. FLU-ENT-CFD code is used as the platform for these simulations and User Defined Functions (UDF) are developed for incorporating this turbulence model into the code. The UDF implementation is validated by simulating several 2-D separated flow/heat transfer benchmark problems. The resulting excellent agreements between the simulated results and benchmark data for these 2-D problems justify the use of this resource for simulating 3-D convection problems. Three-dimensional backward-facing step geometry with an expansion ratio of 1.48 and with a step height of 4.8 mm is used in this study. Three aspect ratios of 3, 8 and infinity (2-D simulation) are considered for studying its effect on the flow and heat transfer, and similarly the effect of the Reynolds number was examined by varying its magnitude in the range of 20,000-50,000. Simulated results are presented for the general 3-D flow features, the reattachment lines, temperature and Nusselt number distributions that develop in this geometry. (C) 2008 Elsevier Ltd. All rights reserved.