In the present work the linear stability analysis of double diffusive convection in a binary fluid layer is performed. The major intention of this study is to investigate the influence of time-periodic vertical vibrations on the onset threshold. A regular perturbation method is used to compute the critical Rayleigh number and wave number. A closed form expression for the shift in the critical Rayleigh number is calculated as a function of frequency of modulation, the solute Rayleigh number, Lewis number, and Prandtl number. These parameters are found to have a significant influence on the onset criterion; therefore the effective control of convection is achieved by proper tuning of these parameters. Vertical vibrations are found to enhance the stability of a binary fluid layer heated and salted from below. The results of this study are useful in the areas of crystal growth in micro-gravity conditions and also in material processing industries where vertical vibrations are involved.
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A numerical solution for the effect of a small but fluctuating gravitational field, characteristic of g-jitter, on the free convection boundary layer flow near the forward stagnation point of a two-dimensional symmetric body resulting from a step change in its surface temperature and immersed in a micropolar fluid is presented in this paper. Both the cases when the spin gradient on the wall is zero and non-zero are considered. The transformed non-similar boundary layer equations are solved numerically by a very efficient implicit finite-difference scheme known as the Keller-box method to investigate the effects on the skin friction and on the rate of heat transfer of variations in the forcing amplitude, a, forcing frequency, 'omega', and micropolar parameter, K. The results are given for a value of the Prandt number Pr=0.7. It has been found that these parameters affect considerably the considered flow characteristics. A comparison with earlier results for a Newtonian fluid (K=0) shows a good agreement.
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