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首页> 外文期刊>International Journal of Heat and Mass Transfer >Vibration effect on the onset of thermal convection in an inhomogeneous porous layer underlying a fluid layer
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Vibration effect on the onset of thermal convection in an inhomogeneous porous layer underlying a fluid layer

机译：振动对流体层下面不均匀多孔层中热对流开始的影响

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摘要

The linear stability problem for a two-layer system consisting of a horizontal pure fluid layer and an inhomogeneous porous layer saturated with the same fluid and heated from below in the presence of vertical high-frequency and small-amplitude vibrations in a gravitational field is studied in the framework of the averaging method. The problem is solved numerically with a shooting method. Bimodal neutral curves of the stability of mechanical equilibrium characterized by the absence of an averaged fluid flow in layers are obtained for the linear profile of porosity within a porous layer and permeability versus porosity through the Carman-Kozeny relation. We consider a competition between perturbations of shorter wavelength (short-wave perturbations) localized mainly in the fluid layer and those of longer wavelength (long-wave perturbations) spanning both layers near the stability threshold in the case when the intensity of vibrations and porosity gradient change. It is shown that when porosity increases with depth, instability is associated with the development of large-scale and long-wave perturbations. The stability threshold of these perturbations weakly depends on the vibration intensity in the range of the parameters considered. Perturbations penetrate into the porous medium poorly when porosity decreases with depth. Vibrations in such a situation stabilize the short-wave instability mode noticeably and lead to an increase in the wavelength of the most dangerous perturbations of equilibrium due to different contributions of inertial effects to fluid and porous layers. It has been found that when the vibration intensity and porosity gradient increase, a hard abrupt transition from short-wave to long-wave perturbations is replaced by a smooth change in the wavelength of critical perturbations related to the loss of stability of equilibrium in the examined two-layer system.
机译：研究了在重力场中存在垂直高频和小振幅振动的情况下，由水平纯流体层和饱和有相同流体并从下方加热的不均匀多孔层组成的两层系统的线性稳定性问题。在平均方法的框架中。用射击方法从数字上解决了这个问题。通过Carman-Kozeny关系，获得了多孔层内孔隙率和渗透率与孔隙率的线性关系，得出了机械平衡稳定性的双峰中性曲线，其特征在于没有分层平均流体流量。在振动强度和孔隙度梯度的情况下，我们考虑主要位于流体层的较短波长的扰动（短波扰动）与跨越两个层的较长波长的扰动（长波扰动）之间的竞争。更改。结果表明，当孔隙度随深度增加时，不稳定性与大规模和长波扰动的发展有关。这些扰动的稳定性阈值在一定程度上取决于所考虑参数范围内的振动强度。当孔隙率随深度减小时，扰动很难渗透到多孔介质中。在这种情况下，振动会显着地稳定短波不稳定模式，并由于对流体层和多孔层的惯性作用不同，导致最危险的平衡扰动的波长增加。已经发现，当振动强度和孔隙度梯度增加时，从短波扰动到长波扰动的硬突然转变被临界扰动波长的平稳变化所代替，该扰动的波长与所研究的平衡稳定性的丧失有关。两层系统。

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