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首页> 外文期刊>International Journal of Heat and Mass Transfer >Vibration effect on double-diffusive instability in an inhomogeneous porous layer underlying a binary fluid layer
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Vibration effect on double-diffusive instability in an inhomogeneous porous layer underlying a binary fluid layer

机译：振动对二元流体层下非均质多孔层中双扩散不稳定性的影响

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A linear stability problem for mechanical equilibrium in an inhomogeneous fluid-saturated porous layer underlying a horizontal binary fluid layer is numerically simulated. The layers are subjected to high-frequency vertical vibration in a gravity field. Different values of temperature and concentration are fixed at the outer impermeable boundaries of the two-layer system. Porosity of a porous layer linearly depends on a transverse z-coordinate. Permeability is given by the Carman-Kozeny formula. To describe a fluid flow in layers, we use the vibrational convection equations written in the Boussinesq approximation and obtained by the averaging method. It is shown that when the fluid is heated from below, vibration effectively increases the equilibrium stability threshold and wavelength of its most dangerous perturbations. If a temperature gradient coincides with the direction of a concentration gradient for the heavier component of binary fluid, average convection is excited in an oscillatory manner. In the opposite case, there is a monotonic instability of equilibrium. Effects of the dimensionless porosity gradient m_z and vibrational parameter p_v on the instability threshold are studied. For p_v < 0.0134 and a fixed solutal Rayleigh number (-5 < R_(mc) ≤ 15) an abrupt jump-like transition from the long-wave to short-wave most dangerous perturbations occurs as mz grows in the range of 0.030-0.162. Long-wave perturbations penetrate both layers. Short-wave perturbations mainly locate in the fluid layer. The transition is smoothed for p_v > 0.0134. When the fluid is heated from above, wavelength of critical perturbations smoothly varies with a change in p_vv and m_z. A convective fluid flow arises monotonously and mostly in the form of long wavelength rolls (a wave number is of k < 3.3). Vibration weakly lowers the equilibrium stability threshold in layers. The effect is most pronounced at high enough Rayleigh numbers (R_m = -40) for a porous medium with the porosity increasing with depth at m_z = -0.2.
机译：数值模拟了水平二元流体层下面的非均质流体饱和多孔层中机械平衡的线性稳定性问题。这些层在重力场中经受高频垂直振动。在两层系统的外部不可渗透边界处固定了不同的温度和浓度值。多孔层的孔隙率线性地取决于横向z坐标。渗透性由Carman-Kozeny公式给出。为了描述层中的流体流动，我们使用以Boussinesq近似表示并通过平均方法获得的振动对流方程。结果表明，当从下面加热流体时，振动有效地增加了平衡稳定性阈值和最危险扰动的波长。如果温度梯度与二元流体中较重组分的浓度梯度方向一致，则平均对流将以振荡方式被激发。在相反的情况下，存在单调的平衡不稳定性。研究了无因次孔隙率梯度m_z和振动参数p_v对不稳定性阈值的影响。当p_v <0.0134且固定瑞利数（-5 0.0134时，过渡平滑。当从上方加热流体时，临界扰动的波长会随着p_vv和m_z的变化而平稳变化。对流流体单调产生，并且主要以长波状波形式出现（波数为k <3.3）。振动微弱地降低了层的平衡稳定性阈值。对于多孔介质，在足够高的瑞利数（R_m = -40）下，这种影响最为明显，其孔隙率随深度在m_z = -0.2处增加。

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