A numerical study of the longitudinal thermoconvective rolls in a mixed convection flow in a horizontal channel with a free surface

This paper presents a numerical study of three-dimensional laminar mixed convection within a liquid flowing on a horizontal channel heated uniformly from below. The upper surface is free and assumed to be flat. The coupled Navier–Stokes and energy equations are solved numerically by the finite volume method taking into account the thermocapillary effects (Marangoni effect). When the strength of the buoyancy, thermocapillary effects and forced convective currents are comparable (Ri ⋍ O(1) and Bd = Ra/Ma ⋍ O(1)), the results show that the development of instabilities in the form of steady longitudinal convective rolls is similar to those encountered in the Poiseuille–Rayleigh–Bénard flow. The number and spatial distribution of these rolls along the channel depend on the flow conditions. The objective of this work is to study the influence of parameters, such as the Reynolds, Rayleigh and Biot numbers, on the flow patterns and heat transfer characteristics. The effects of variations in the surface tension with temperature gradients (Marangoni effect) are also considered.

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► A Poiseuille–Rayleigh–Bénard–Marangoni flow in an open horizontal channel was modeled.
► Formation of longitudinal convective rolls as for a Poiseuille–Rayleigh–Bénard flow.
► The parietal heat transfer is enhanced by onset of the longitudinal rolls.
► Large Marangoni effect was found to reduce the rolls number by merging.
► Thermocapillary forces reverse the rotation of the rolls near the lateral walls.