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Transient Flow Conjugated with Mixed Convection in a Vertical Channel
Дата публикации: 13-07-2026 22:00:00

Publication date: 14 July 2026
Source: Defect and Diffusion Forum Vol. 453
Author(s): Sofiane Boulkroune, Abdelfetah Belaid, Abdelkader Filali, Omar Kholai, Tawfiq Chekifi, Mawloud Guermoui, Reski Khelifi
Transient laminar mixed convection of air (Pr = 0.71) in a vertical plane channel is numerically investigated for opposing buoyancy at Re=100. The channel walls include symmetric, discrete, isothermal heated sections applied on the external side of a central wall zone, resulting in a conjugate heat-transfer problem through the solid wall and the fluid domain. The two-dimensional unsteady Navier–Stokes and energy equations are solved using a finite-volume method on a staggered grid with SIMPLE pressure–velocity coupling. The Grashof number is varied over 103 ≤ Gr ≤ 105. Instability onset is identified using a quantitative criterion based on the growth and persistence of velocity/temperature fluctuations and a domain-integrated fluctuation energy. The effects of wall thickness Δ and heated length Lh on the critical Grashof number are reported. Increasing Lh lowers the instability threshold, whereas increasing Δ stabilizes the flow by damping thermal gradients transmitted to the fluid. The results provide a stability map and physical interpretation of the transition from steady to unsteady mixed convection at low Reynolds number.


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