The fluid dynamics and thermodynamics of eruption columns
The fluid dynamics and thermodynamics of eruption columns
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喷发柱的流体动力学和热力学
DOI：
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发表时间：
1988
期刊：
影响因子：
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通讯作者：
A. Woods
中科院分区：
文献类型：
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作者：
A. Woods
从第一性原理出发，导出了一种新的普林尼火山喷发柱模型，并进行了数值研究。动量驱动的基底“气冲区”和上部浮力驱动的对流区所特有的动力学分别进行了处理。柱内的热相互作用用定常流动-能量方程来模拟。本文的主要研究结果表明：(1)基底气冲区模型预测物质在离开喷口时的初始膨胀速度非常快；(2)气体推力区高度随初始温度、喷发物质初始含气量和初始速度的增大而减小，随喷发半径的增大而增大；(3)塔总高度随初始温度、初始速度和排气半径的增大而增大，随初始含气量的增大而减小；(4)初速度为100 m/s数量级时，柱体发生崩塌；精确值随着喷发物质中初始气体含量的降低而增加；(5)对于喷口半径较大或喷出物料初始含气量较低的情况，在浮力驱动区，塔内流速可以随高度增加一次，而不是单调衰减为零；(6)塔中上部的热相互作用以势能与焓的相互作用为主。以前的喷发柱模型存在不一致性和简化；与目前的模型相比，这些因素导致了结果的显著差异。
A new model for Plinian eruption columns is derived from first principles and investigated numerically. The dynamics particular to the momentum-driven basal ‘gas-thrust region’ and the upper buoyancy-driven convective region are treated separately. The thermal interactions in the column are modelled by the steady-flow-energy equation. The main results of the present paper are that: (1) the basal gas-thrust region model predicts a very rapid initial expansion of the material on leaving the vent; (2) the gas-thrust region height decreases with initial temperature, inital gas content of the erupted material and initial velocity, but increases with vent radius; (3) the total column height increases with initial temperature, initial velocity and vent radius, but decreases with initial gas content; (4) column collapse occurs for initial velocities of the order of 100 m/s; the precise value increases as the initial gas content in the erupted material decreases; (5) for large vent radii or low initial gas content of the erupted material, the velocity in the column can increase with height once in the buoyancy-driven region instead of decaying to zero monotonically; (6) the interaction of the potential energy with the enthalpy is found to be the dominant thermal interaction in the upper part of the column. Previous models of eruption columns involve inconsistencies and simplifications; these are shown to lead to significant differences in the results in comparison to the present model.