Oscillatory dou biffusive natural convection in low prandtl number fluid

摘要

The numerical simulations of double-diffusive natural convection were carried out at the Prandtl number Pr=0.01 and the Lewis number Le=100 for two models. One is a two-layer system which consists of a pure liquid (upper layer) and a solution (lower layer) by lateral heating and cooling at an aspect ratio A=4 and a buoyancy ratio N=10. The double-diffusive natural convection was monotonous at the Rayleigh number Ra=10~4 but the double-oscillatory characteristic was found at Ra=10~5. The short periodic oscillation corresponded to the oscillatory flow and the long periodic oscillation corresponded to the migration (collision and rebound) of roll cells. The other model is the case of opposing buoyancy forces near the vertical walls at Ra=10~4. At A=1 the thermal convection was formed at N=1 and 2; the thermal and solutal convections coexisted at N=3; the solutal convection became dominant with the formation of concentration stratified layer at N=5. However the flow at A=2 was oscillatory for N=1 to 10 and the intensity of oscillation became weak at N >= 3. The intensity of flow oscillation at A=2 was generally stronger than that at A=1.