Two-layer thermal convection in miscible viscous fluids

摘要: The influence of a viscosity stratification on the interaction between thermal convection and stable density discontinuity is studied, using laboratory experiments. Initially, two superposed isothermal layers high-Prandtl-number miscible fluids are suddenly cooled from above heated below. By adjusting concentrations salt cellulose, Rayleigh numbers 300 3×10 7 were achieved for contrasts 0.45 % 5 ratios 1 6.4×10 4 . Heat mass transfer through interface monitored. Two-layer observed but steady state never obtained since penetrative occurs. A new interfacial instability reported, owing to nonlinear interaction unstable chemical density gradients. As result, temperature condition at highly inhomogeneous, driving, top classical small-scale convection, large-scale flow in each layer which produces cusps interface. Entrainment, driven by viscous coupling layers, proceeds those cusps. pattern entrainment asymmetric: two-dimensional sheets dragged into more viscous layer, while three-dimensional conduits produced less layer. simple entrainment model proposed scaling laws rate derived; they explain experimental data well.