Pressure-driven gas ow in viscously deformable porous media: application to lava domes
Pressure-driven gas ow in viscously deformable porous media: application to lava domes
复制标题
粘性可变形多孔介质中的压力驱动气体流动：在熔岩穹顶中的应用
DOI：
10.1017/jfm2019-211
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发表时间：
2019
影响因子：
3.7
通讯作者：
Pitman, E.B
中科院分区：
文献类型：
--
作者：
Hyman, D.;Bursik, M.;Pitman, E.B
本文研究了粘性变形多孔介质中低粘度、压力驱动的可压缩孔隙流体流动的特性，并将其具体应用于熔岩丘中的气体流动。的气体和熔岩的组合流被示出由两个方程组的非线性混合双曲抛物型偏微分方程描述的气体孔隙压力和熔岩孔隙度的演变。当气体孔隙压力为岩浆静压力时，该系统的稳态解得以实现，并且孔隙度剖面通过介质随深度的增加而增加的压实来适应岩浆静压力条件。一维（垂直）数值线性稳定性分析（LSA）。由于孔隙流体的可压缩性和重力压实的存在，存在于稳态解中的梯度导致线性化方程中的可变系数，该线性化方程产生LSA中的不稳定性，尽管在原始系统中存在扩散和耗散项。这种不稳定性的发病被示出强烈控制的厚度的流量和最大孔隙率，本身的气体的质量流率的函数。完全非线性系统的数值解，并表现出非线性波传播的特点，如冲击形成。当应用于熔岩圆顶内的气体流动时，这种动力学的细节有助于解释周期性熔岩圆顶挤出和爆炸事件的观察结果。由于不稳定性在较厚的流动中更强，熔岩圆顶的持续挤压和增厚构成了不稳定性开始、压力波增长和最终爆炸的可能性增加。
The behaviour of low-viscosity, pressure-driven compressible pore fluid flows in viscously deformable porous media is studied here with specific application to gas flow in lava domes. The combined flow of gas and lava is shown to be governed by a two-equation set of nonlinear mixed hyperbolic–parabolic type partial differential equations describing the evolution of gas pore pressure and lava porosity. Steady state solution of this system is achieved when the gas pore pressure is magmastatic and the porosity profile accommodates the magmastatic pressure condition by increased compaction of the medium with depth. A one-dimensional (vertical) numerical linear stability analysis (LSA) is presented here. As a consequence of the pore-fluid compressibility and the presence of gravitation compaction, the gradients present in the steady-state solution cause variable coefficients in the linearized equations which generate instability in the LSA despite the diffusion-like and dissipative terms in the original system. The onset of this instability is shown to be strongly controlled by the thickness of the flow and the maximum porosity, itself a function of the mass flow rate of gas. Numerical solutions of the fully nonlinear system are also presented and exhibit nonlinear wave propagation features such as shock formation. As applied to gas flow within lava domes, the details of this dynamics help explain observations of cyclic lava dome extrusion and explosion episodes. Because the instability is stronger in thicker flows, the continued extrusion and thickening of a lava dome constitutes an increasing likelihood of instability onset, pressure wave growth and ultimately explosion.