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首页> 外文期刊>Journal of Volcanology and Geothermal Research >3-D numerical simulations of eruption column collapse: Effects of vent size on pressure-balanced jet/plumes
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3-D numerical simulations of eruption column collapse: Effects of vent size on pressure-balanced jet/plumes

机译：喷发柱塌陷的3-D数值模拟：喷口尺寸对压力平衡的射流/羽流的影响

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摘要

Buoyant columns or pyrodastic flows form during explosive volcanic eruptions. In the transition-state, these two eruption styles can develop simultaneously. We investigated the critical condition that separates the two eruption styles (referred to as "the column collapse condition") by performing a series of three-dimensional numerical simulations. In the simulation results, we identify two types of flow regime: a turbulent jet that efficiently entrains ambient air (jet-type) and a fountain with a high-concentration of the ejected material (fountain-type). Hence, there are two types of column collapse (jet-type and fountain-type). Which type of collapse occurs at the column collapse condition depends on whether the critical mass discharge rate for column collapse (MDRcc) is larger or smaller than that for the generation of a fountain (MDR_(JF)) for a given exit velocity. Temperature controls the relative magnitude of MDRcc relative to MDR_(JF), and hence the type of collapse. For given magma properties (e.g., temperature and water content), the column collapse condition is expressed by a critical value of the Richardson number (Ricc=g'_0L_0/W_0~2, where g'_0 is the source buoyancy, L_0 is the vent radius, and w_0 is the exit velocity). When the jet-type collapse occurs at the column collapse condition, Ri_(CC) is independent of the exit velocity. When the fountain type collapse occurs at the column collapse condition, on the other hand, Ri_(CC) decreases as the exit velocity increases. As the exit velocity exceeds the sound velocity, a robust flow structure with a series of standing shock waves develops in the fountain, which suppresses entrainment o ambient air and enhances column collapse.
机译：在爆炸性火山喷发过程中会形成浮柱或热成岩流。在过渡状态下，这两种喷发方式可以同时发展。通过执行一系列三维数值模拟，我们研究了区分两种喷发类型的临界条件（称为“列塌陷条件”）。在模拟结果中，我们确定了两种流态：一种有效地夹带环境空气的湍流射流（射流型）和一种具有高浓度喷射物质的喷泉（喷泉型）。因此，有两种类型的柱塌陷（喷射型和喷泉型）。在给定的出口速度下，哪种类型的塌陷发生在色谱柱塌陷条件下，取决于色谱柱塌陷的临界质量排放速率（MDRcc）大于生成喷泉的临界质量排放速率（MDR_（JF））。温度控制着MDRcc相对于MDR_（JF）的相对大小，因此控制了塌陷的类型。对于给定的岩浆特性（例如温度和水含量），列坍塌条件由理查森数的临界值表示（Ricc = g'_0L_0 / W_0〜2，其中g'_0是源浮力，L_0是出口半径，w_0是出口速度）。当在柱塌陷条件下发生喷射型塌陷时，Ri_（CC）与出口速度无关。另一方面，当在柱塌陷状态下发生喷泉型塌陷时，Ri_（CC）随着出口速度的增加而减小。当出口速度超过声速时，在喷泉中会形成带有一系列驻波的稳健流动结构，从而抑制环境空气的夹带并增加柱塌陷。

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