OSCILLATORY DOUBLE-DIFFUSIVE CONVECTION IN A RECTANGULAR ENCLOSURE WITH COMBINED HORIZONTAL TEMPERATURE AND CONCENTRATION GRADIENTS

The effect of buoyancy ratio on the flow structure is investigated num erically for a binary mixture gas in a rectangular enclosure subject t o opposing horizontal thermal and compositional buoyancies. The follow ing conditions were considered: Ra-T = 10(5), Pr = 1, Le = 2 and N = 0 .0-2.0 for A = 2. The numerical solution predicts that oscillatory dou ble-diffusive convection with the secondary cell flow structure occurs for a certain range of buoyancy ratio. The key mechanism for oscillat ory flow is that the unstably stratified region of species shifts from the central part of the enclosure to the upper and lower parts, and v ice versa in a time-periodic sense, due to the interaction of heat and mass transfer with different diffusivities near the vertical walls. B ifurcation structures of the oscillatory flow in the present system ar e discussed. (C) 1998 Elsevier Science Ltd. All rights reserved.