The numerical simulation of a baseline ribbed duct with conventional ribs is investigated and compared to a rib with a forward step. Mean flow, turbulent statistics and heat transfer performance are compared by using the WALE model (Wall Adaptive LES). The geometry consists of a square duct with rib height to hydraulic diameter ratio of 0.1 and rib pitch-to-rib height ratio of 10. The rib step ratio (step height/rib height) of 0.5 is placed at both the bottom and top walls. The calculations are performed for a nominal bulk Reynolds number of 20,000 with constant heat flux boundary conditions. Hydrodynamic and thermally fully-developed conditions are assumed. A mesh resolution of 653 is tested for the for WALE. Time evolution, mean, and turbulent quantities, heat transfer coefficient and friction factor are presented and compared for the two geometries. © 2019 Begell House Inc. All rights reserved.