Effect of the fin length on natural convection flow transition in a cavity

• The flow adjacent to the finned sidewall of a differentially heated cavity is numerically investigated.
• The flow is unsteady if the Rayleigh number is higher than a critical value.
• The transition from a steady to an unsteady flow is sensitive to the fin length.
• The critical values of the transition for the different fin lengths are obtained.

In this study we investigate the transition from a steady flow to an unsteady flow induced by an adiabatic fin on the sidewall of a differentially heated cavity using numerical simulation. A range of Rayleigh numbers (106–109) and various fin lengths with Prandtl number 6.63 are considered. It is found that the flow adjacent to the finned sidewall is unsteady for the cases with Rayleigh numbers higher than a critical value for a given fin length. Such an unsteady flow results from a fluid layer above the fin with an adverse temperature gradient and a through flow, which is a similar mechanism to a Rayleigh–Benard–Poiseuille (RBP) flow, though the configuration is such that it cannot be exactly a RBP flow. The transition from a steady flow to an unsteady flow is sensitive to the fin length, and the critical values of the transition for the different fin lengths are obtained. Moreover, the features of the unsteady flow induced by the fin are characterized and the mechanisms responsible for the unsteadiness are discussed.