Convective mixing in vertically-layered porous media: The linear regime and the onset of convection
- Univ. of Maryland, College Park, MD (United States). Dept. of Mechanical Engineering
- Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
In this paper, we study the effect of permeability heterogeneity on the stability of gravitationally unstable, transient, diffusive boundary layers in porous media. Permeability is taken to vary periodically in the horizontal plane normal to the direction of gravity. In contrast to the situation for vertical permeability variation, the horizontal perturbation structures are multimodal. We therefore use a two-dimensional quasi-steady eigenvalue analysis as well as a complementary initial value problem to investigate the stability behavior in the linear regime, until the onset of convection. We find that thick permeability layers enhance instability compared with thin layers when heterogeneity is increased. On the contrary, for thin layers the instability is weakened progressively with increasing heterogeneity to the extent that the corresponding homogeneous case is more unstable. For high levels of heterogeneity, we find that a small change in the permeability field results in large variations in the onset time of convection, similar to the instability event in the linear regime. However, this trend does not persist unconditionally because of the reorientation of vorticity pairs due to the interaction of evolving perturbation structures with heterogeneity. Consequently, an earlier onset of instability does not necessarily imply an earlier onset of convection. A resonant amplification of instability is observed within the linear regime when the dominant perturbation mode is equal to half the wavenumber of permeability variation. On the other hand, a substantial damping occurs when the perturbation mode is equal to the harmonic and sub-harmonic components of the permeability wavenumber. Finally, the phenomenon of such harmonic interactions influences both the onset of instability as well as the onset of convection.
- Research Organization:
- Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
- Sponsoring Organization:
- USDOE
- Grant/Contract Number:
- AC52-06NA25396
- OSTI ID:
- 1374329
- Report Number(s):
- LA-UR-17-21307
- Journal Information:
- Physics of Fluids, Vol. 29, Issue 8; ISSN 1070-6631
- Publisher:
- American Institute of Physics (AIP)Copyright Statement
- Country of Publication:
- United States
- Language:
- English
Web of Science
Comparison of free convection flow around an engineered porous fin with spherical connections and rigid fin under different positioning angles—An experimental and numerical analysis
|
journal | March 2019 |
On the selection of perturbations for thermal boundary layer control
|
journal | October 2019 |
Generalized regimes for the formation of stratified regions during freezing of multi-component mixtures
|
journal | December 2019 |
On the selection of perturbations for thermal boundary layer control
|
text | January 2019 |
Similar Records
Evaporation-wind feedback and the organizing of tropical convection on the planetary scale. Part II: Nonlinear evolution
Linear stability analysis of two fluid columns of different densities and viscosities in a gravity field