Unsteady mixed convection in a horizontal channel with rectangular blocks periodically distributed on its lower wall

We present a numerical study of laminar unsteady mixed convection in a two dimensional horizontal channel containing heating blocks periodically mounted on its lower wall while its upper wall is maintained cold at a constant temperature. The flow is assumed to be fully developed and periodic conditions are used in the longitudinal direction of the channel. The parameters governing the problem are the Reynolds number (0.1⩽Re⩽200), the Rayleigh number (104⩽Ra⩽106) and the relative height of the blocks (0.25⩽B=h′/H′⩽0.5). The effect of the forced flow on the natural convection cells is studied for different values of the governing parameters. The conditions corresponding to the displacement of these cells and the unsteadiness of the flow are determined. The fully developed forced flow is found to reduce considerably the heat transfer through the cold surface of the channel at relatively large Re.