要約

Two mechanisms of roll initiation are highlighted in a horizontal channel flow, uniformly heated from below (Γ=10, Pr=7, Re=50, 0≤Ra≤10⁵). The first mechanism is the classical one, it occurs for low Rayleigh numbers and is initiated by the lateral wall effect. The second occurs for higher Rayleigh numbers and combines the previous effect with a supercritical vertical temperature gradient in the lower boundary layer, which simultaneously triggers pairs of rolls in the whole zone in between the two lateral rolls. Consequently, the heat transfer is significantly enhanced compared to the pure forced convection case owing to the flow pattern responsible of the continuously flooding the heated wall with cold fluid.