LBM simulation of stabilizing/destabilizing effects of thermodiffusion and heat generation in a rectangular cavity filled with a binary mixture

摘要

A special case that stands out in thermosolutal convection is that for which the thermal and solutal convection forces are equal and generate opposite effects (N == -1). This antagonistic effect between the two buoyancy forces is expected to generate unpredictable and unique behaviors when combined with thermodiffusion and internal heating phenomena. The present numerical study is dedicated to this particular case considering a binary mixture confined in a vertical rectangular cavity with an aspect ratio A = 2. The lattice Boltzmann method with multiple relaxation time is used to analyze the effect of the control parameters which are the Soret parameter (Sr = -0.5, 0 and 0.5), and the internal to external Rayleigh numbers ratio (0 ≤ R ≤ 80) while maintaining constant the external Rayleigh number (Ra_E = 10~5), the Prandtl number [Pr = 0.71) and the Lewis number (Le = 2). The results obtained show that, in the absence of Soret effect, there are three small ranges of R characterized by flow instabilities. These ranges are located below R = 1.85. The increase of R may accentuate or attenuate the complexity of the oscillations depending on the range of the heating parameter. It is also shown that the positive value of the Soret parameter leads to a stabilizing effect of thermodiffusion by eliminating the instabilities, while the negative value of this parameter engenders an extension of the instability range until R = 20, accompanied by important changes in terms of behaviors.