Mixed Convection in a Differentially Heated Cavity with Local Flow Modulation via Rotating Flat Plates

Abstract: Mixed Convection inside a cavity resulting from thermal buoyancy force under local modulation via rotating flat plate has been investigated. The present model consists of a square cavity with the left and right vertical walls fixed at constant high and low temperatures respectively while the top and bottom walls are supposed to be adiabatic. Two clockwise rotating flat plates, having negligible thickness in comparison to their lengths, acting as flow modulators have been placed vertically along the centerline of the cavity. The moving boundary problem due to plate motion in this study has been solved by implementing \textit{Arbitrary Lagrangian Eulerian (ALE)} finite element formulation with triangular discretization scheme.Simulations are conducted for air ($Pr=0.71$) at different Rayleigh numbers ($10^2 \leq Ra \leq 10^6$). Rotational Reynolds number based on plate dynamic condition has been considered to be constant at 430. Numerical results identify critical Rayleigh number $Ra_{cr}=0.41\times10^6$ beyond which two smaller flow modulators are more effective than a single larger modulator. Thermal oscillating frequency was observed to be insensitive to Rayleigh number for the case of double modulators.