Three-dimensional numerical simulation of double-diffusive Rayleigh-Bénard convection in a cylindrical enclosure of aspect ratio 2

This paper presented a series of three-dimensional numerical simulations on the double-diffusive Rayleigh-Bénard convection in a cylindrical enclosure filled with the isopropanol/water mixture with an initial mass fraction of 10%. The Prandtl number and the Lewis number of the isopropanol/water mixture were 13.2 and 140.2, respectively. The cylindrical enclosure was heated at the bottom wall and cooled at the top wall. Results show that the ratio of the solutal buoyancy to thermal buoyancy has an important effect on flow pattern formation and bifurcation sequences. For cooperating buoyancy convection, an unsteady flow appears foremost, and then four typical steady flow patterns happen orderly. For opposing buoyancy convection, only five types of oscillatory flow patterns are detected, which are characterized by azimuthal rotation. The critical Rayleigh number at the primary threshold is strongly influenced by concentration gradient, and decreases with the increase of the buoyancy ratio. Different solution branches are denoted in terms of the Nusselt number, which depends primarily on the Rayleigh number and the flow pattern. Furthermore, the several flow pattern coexistence and hysteresis phenomenon of the flow pattern transition in double-diffusive Rayleigh-Bénard convection have also been confirmed.