Modelling the rapid near-surface expansion of gas slugs in low-viscosity magmas
Modelling the rapid near-surface expansion of gas slugs in low-viscosity magmas
复制标题
模拟低粘度岩浆中气体段塞的快速近地表膨胀
DOI：
--
复制
发表时间：
2008
期刊：
影响因子：
--
通讯作者：
S. Corder
中科院分区：
文献类型：
--
作者：
M. James;S. Lane;S. Corder
摘要 使用 1D 数学和 3D 计算流体动力学 (CFD) 模型模拟垂直圆柱形管道和低粘度岩浆中大气泡（段塞）的上升。根据实验室证据，一维模型定义了段塞底部的恒定上升速度，并允许气体膨胀在上升过程中加速段塞鼻穿过上覆流体。在实验室实验中观察到的快速膨胀气体段塞的演化过程得到了很好的再现，并且在火山尺度上，可以预测多个大气层的地表超压，而不需要任何深度的初始超压。近地表动力学使弹头穿过上覆岩浆的速度增加了 c 倍。 2.5 气体膨胀导致爆发前岩浆表面速度为 c。 35米秒−1。为了检查压力分布和施加在管道上的力，进行了 3D CFD 模拟。在火山尺度上，最终段塞上升到地表期间的垂直单力为 c。 106 N，比斯特龙博利超长周期地震事件相关的震级小两个数量级。这支持了之前对这些事件的解释，即它们是由流过管道几何形状变化的气体段塞产生的，而不是段塞喷发过程的直接结果。
Abstract The ascent of large gas bubbles (slugs) in vertical cylindrical conduits and low-viscosity magmas is simulated using 1D mathematical and 3D computational fluid dynamic (CFD) models. Following laboratory evidence, the 1D model defines a constant rise velocity for the slug base and allows gas expansion to accelerate the slug nose through the overlying fluid during ascent. The evolution of rapidly expanding gas slugs observed in laboratory experiments is reproduced well and, at volcano scales, predicts at-surface overpressures of several atmospheres without requiring any initial overpressure at depth. The near-surface dynamics increase slug nose velocities through the overlying magma by a factor of c. 2.5 and the gas expansion results in pre-burst magma surface velocities of c. 35 m s−1. To examine pressure distributions and the forces exerted on a conduit, 3D CFD simulations were carried out. At volcano scales, the vertical single forces during final slug ascent to the surface are c. 106 N, two orders of magnitude smaller than those associated with very-long-period seismic events at Stromboli. This supports a previous interpretation of these events in which they are generated by gas slugs flowing through changes in conduit geometry, rather than being the direct result of slug eruption processes.