The convective double-diffusive instability in a two-layer system consisting of a binary fluid layer overlaying a fluid-saturated porous layer is investigated numerically. The system moves periodically in a vertical direction under the conditions of gravity field. The layers are heated from below and oscillate with high frequency and small amplitude. The instability threshold for the convection onset and the wavelength of convective rolls, which induce as soon as the fluid equilibrium state has lost its stability, are found. The buoyancy ratio and vibrational parameter effects are studied. A region of parameters for the bimodal marginal stability curves is obtained and divided it into parts for the local and large-scale convection onset values. It is revealed that wavelength of stationary convection rolls varies non-monotonically as the buoyancy ratio decreases. The longitudinal scale of rolls reduces sharply at first and then increases gradually. Vibration produces the greatest stabilizing effect on the fluid equilibrium state in a narrow range of small negative and positive buoyancy ratios, which are responsible for a considerable change in the wavelength of rolls. The buoyancy ratio effect on the oscillatory convection rolls is rather weak. The vibration effect on their marginal stability threshold and wavelength is more pronounced.

中文翻译：

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从下方加热的叠加流体多孔层中振动双扩散不稳定性的两种模式：浮力比的影响

数值研究了由覆盖流体饱和多孔层的二元流体层组成的两层系统中的对流双扩散不稳定性。系统在重力场条件下沿垂直方向周期性运动。这些层从下方加热并以高频率和小幅度振荡。找到了对流开始的不稳定阈值和对流卷的波长，一旦流体平衡状态失去稳定性，就会引起对流卷的波长。研究了浮力比和振动参数的影响。获得了双峰边缘稳定性曲线的参数区域，并将其分为局部和大规模对流起始值的部分。结果表明，随着浮力比的降低，固定对流辊的波长非单调变化。轧辊纵向尺度先急剧减小后逐渐增大。在较小的负浮力比和正浮力比的狭窄范围内，振动对流体平衡状态产生最大的稳定作用，这是导致滚动波长发生显着变化的原因。对振荡对流卷的浮力比影响相当微弱。振动对其边际稳定性阈值和波长的影响更为明显。这导致卷的波长发生相当大的变化。对振荡对流卷的浮力比影响相当微弱。振动对其边际稳定性阈值和波长的影响更为明显。这导致卷的波长发生相当大的变化。对振荡对流卷的浮力比影响相当微弱。振动对其边际稳定性阈值和波长的影响更为明显。