一种考虑三相的具有赫谢尔-布克利流变学的瞬态深度平均熔岩流模型
A transient depth-averaged lava flow model with a Herschel-Bulkley rheology accounting for three phases
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中文总结 AI 辅助
研究提出含晶体和气泡的三相悬浮熔岩流模型，有两种晶体体积分数演化封闭方法，推导求解一维深度平均模型。与现有模型对比，温度多参数演化预测更准，模型能体现熔岩流脉动性，还探讨了气泡对粘度的影响。
中文摘要 AI 辅助
本研究提出了一种具有赫谢尔-布克利流变学的三相悬浮熔岩流模型。悬浮液包含晶体和气泡，考虑了两种晶体体积分数演化的封闭方法。第一种通过将晶体分数视为受松弛趋于平衡状态的输运量来最小化系统复杂性，避免了熔岩流所经历的多种传热机制的参数化。另一种基于考虑四种传热机制和规定的温度-结晶度关系来处理熔岩温度。由此推导并数值求解了一维深度平均模型。与基于实际熔岩流数据的现有模型比较表明，用温度的多参数演化预测流动参数比另一种封闭方法更准确。模型的瞬态性质正确预测了受限熔岩沿不规则陡坡流动会产生一系列级联的填充然后破裂的团块，导致整体流动呈脉动性。理论上，考虑气泡最好采用在任何毛细管数下都有效的一般流变关系。在此探索的条件下，气泡以剪切变稀行为将粘度调节在2倍因子内，使慢流减速、快流加速。当使用将气泡视为硬球的简化流变学时，唯一受影响的动态参数是体积粘度。
英文摘要
This study presents a three-phase suspension lava flow model with a Herschel-Bulkley rheology. The suspension contains crystals and gas bubbles, and two closures for the evolution of the crystal volume fraction are considered. The first closure minimizes the complexity of the system by treating crystal fraction as a transported quantity subject to relaxation towards an equilibrium state. This closure avoids a parametrization of the many heat transfer mechanisms a lava flow is subjected to. The other closure is on the lava temperature considering four heat transfer mechanisms and a prescribed temperature--crystallinity relationship. We deduce from this system and solve numerically a one-dimensional depth-averaged model. A comparison with a pre-existing model based on real lava flow data suggests that the prediction of flow parameters done with the multi-parametric evolution of temperature yields more accurate results than those obtained with the other closure. The transient nature of our model correctly predicts that confined lava traveling down an irregular steep slope yields a series of cascading fill-then-breakout lumps that causes the overall flow to be pulsatory. These pulses dominate the local dynamics and preclude a strict steady state to be reached. Theoretically, taking gas bubbles into account is best done with a general rheological relationship valid at any capillary number. In the conditions explored herein, bubbles modulate viscosity within a factor 2 with a shear thinning behavior, decelerating slow flows and accelerating fast flows. When a simplified rheology treating bubbles as hard spheres was used, the only dynamic parameter affected was bulk viscosity.
