Fluid dynamics in explosive volcanic vents and craters
Fluid dynamics in explosive volcanic vents and craters
复制标题
爆炸性火山喷口和火山口的流体动力学
DOI：
10.1016/j.epsl.2011.10.032
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发表时间：
2011
影响因子：
5.3
通讯作者：
D. Ogden
中科院分区：
文献类型：
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作者：
D. Ogden
爆发性火山喷流可以转变为浮力羽流或坍塌形成火山碎屑密度流，这取决于它们夹带和加热环境空气的能力。最近的一维（1D）分析表明，通过火山口和火山口的流体加速足以改变这些射流内的速度和压力，足以成为对羽流尺寸的一阶控制，因此空气夹带和柱稳定性（Koyaguchi等人，2010年）。这些一维研究仅适用于与垂直方向夹角小于约30°的火山口和喷口。使用解析公式和数值模拟，这项研究描述了2D效果浅倾斜的火山口和火山口的火山爆发。喷口对火山灰和气体的喷发混合物的加速和膨胀的影响被描述为喷口壁对流体施加的力，即壁力（Fw）。这个力是衡量火山喷发和火山口中发生的固体地球之间的动量耦合的一种方法。通过Prandtl-Meyer膨胀，在浅倾喷口内的超音速喷发流体发生快速发散，这导致与一维分析预测的压力和速度场不同。这种膨胀降低了Fwand垂直加速度所经历的喷发流体在喷口。对于通过一维分析预测的以超音速和大气压离开喷口的射流，Fw的减小将导致预测的羽流面积增加，从而降低柱稳定性。火山口的复杂2D形状可以改变射流结构（冲击波的存在和位置），并排除在没有内部驻冲击波的情况下超音速离开喷口的射流的发展（即，完全膨胀或压力平衡的射流）。喷流结构的这些显著复杂性和羽流半径的增加可能导致空气卷吸、羽流稳定性和火山灰分布的变化。
Explosive volcanic jets can transition to buoyant plumes or collapse to form pyroclastic density currents depending on their ability to entrain and heat the ambient air. Recent one-dimensional (1D) analysis shows that fluid acceleration through volcanic vents and craters changes the velocity and pressures within these jets sufficiently enough to be a first order control on plume dimensions and therefore air entrainment and column stability (Koyaguchi et al., 2010). These 1D studies are only applicable to craters and vents with angles of less than about 30° to vertical. Using analytical formulations and numerical simulations, this study describes 2D effects of shallowly dipping vents and craters on volcanic eruptions. The effect of vents on acceleration and expansion of eruptive mixtures of ash and gas is described as a force imparted on the fluid by the vent wall, the wall force (Fw). This force is a measure of the momentum coupling between an eruption and the solid earth that takes place in the vent. Rapid divergence of supersonic eruptive fluid within shallowly dipping vents occurs via Prandtl–Meyer expansion, which results in different pressure and velocity fields than those predicted by 1D analysis. This expansion decreases Fwand the vertical acceleration experienced by the eruptive fluid in the vent. For jets predicted by 1D analysis to exit the vent at supersonic velocities and at atmospheric pressure, this decrease in Fwwill cause an increase in the predicted plume area, decreasing column stability. The complex 2D shape of volcanic vents can change jet structure (presence and location of shock waves) and preclude the development of jets that exit the vent supersonically with no internal standing shock waves (i.e., perfectly expanded or pressure balanced jets). These significant complications in jet structure and increase in plume radius may result in changes to air entrainment, plume stability, and tephra distribution.