Date of Publication :7th December 2025

Abstract: Numerical Investigations were carried out to study the Evolution of plume structure in Rayleigh-Benard convection at a constant Pr = 5.2 (water) and over a range of Rayleigh number 4.43 ×105 < RaH < 7.95 × 108. Three domains of cross-section 15 cm × 15 cm and height of 5 cm, 10 cm and 20 cm were used to study the plume structure rising from the thermal boundary layer over the high- temperature bottom plate. Transient simulations were carried out in ANSYS Fluent to study the evolution of plume structures. Four different regimes where observed viz, initiation phase; characterised by stable boundary layer across the planform, impingement phase; characterised by the destabilisation of the boundary layer and impingement of bulk flow, plume formation phase; characterised by the formation of line plume from the boundary layer, and plume dynamics phase; characterised by the lateral movement of plume, formation of new plumes and merging of plumes. Total length of plume (Lp) and plume thickness (tp) were measured from the planforms, and mean plume spacing (λ) and plume area ratio (Ap/A) were calculated using λ =A/ Lp and Ap/A = tp×Lp / A. Total length of plume was found to increase with RaH, whereas mean plume thickness was found to decrease with RaH; these opposing trends result in plume area ratio nearly independent of RaH.

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