Numerical Simulations of Natural Convection in Vertical Cavities

Abstract

Convection is natural phenomenon involved in solar granulation, atmospheric structuring of planets, continental drift, striations in crystal growth, flame structure, atmospheric circulation etc. The study of convection phenomenon has vital importance in disciplines of meteorology, oceanography, geophysics and astrophysics. The most common and simplest case of natural convection occurs in a fluid layer due to vertical temperature gradient, when the lower wall is heated and the upper wall cooled and is termed as the Rayleigh Benard Convection (RBC). The RBC is investigated in 2D vertical enclosed cavity with horizontal temperature gradient, with right wall at higher temperature than left wall and other two adiabatic walls for various vertical aspect ratios for . The velocity field, horizontal and vertical velocity, temperature field and number behaviors are studied and discussed for various cases of . It is established that in the case under study, convection starts at critical . It is also found that at lower numbers, the fluid motion inside cavity is restricted to proximity of walls only; the core has conduction in it. Gradually with increasing number, the convection covers the whole cavity including the core zone and at number equals to , instabilities sets in the cavity at and beyond critical aspect ratio ( ). Beyond this instability point, secondary cells are formed in the cavity which decreases in number as number increases, until the flow is fully turbulent. It is noticed in this numerical study that the laminar and transition regimes shrinks as the increases and flow tends to become random at relatively lower numbers for higher . The comparison of average numbers for different tends to show smoother slopes at higher vertical till instability point, and become aggressively random beyond this point on log versus log graph.