Hydrodynamic features of the gas flows past a rib and past a downward step in characteristic separation-flow regions, and distributions of pressures, temperatures, and heat-transfer coefficients behind the obstacles in such flows were experimentally studied. A comparative analysis of the intensifying action of ribs and steps on convective heat transfer is given. We also examined the effect of enhanced external turbulence on thermal and dynamic characteristics of the separated flows. An increased level of free-stream turbulence suppresses the flow separation. The high free-stream turbulent intensifying effect turned out to be more pronounced for the flow past a downward step. (C) 2003 Elsevier Ltd. All rights reserved.