arXiv 1610.093522016-10-28physics.flu-dynnlin.AOnlin.PSphysics.geo-ph

在地幔对流实验室模拟中粘度差对地幔柱结构的作用

The role of viscosity contrast on plume structure in laboratory modeling of mantle convection

Vivek N. Prakash, K. R. Sreenivas, Jaywant H. Arakeri

备注：: Preprint accepted in Chemical Engineering Science, 19 pages with 9 figures, and an additional 18 pages of supplementary material
发表信息：: Chemical Engineering Science, 158, 245-256 (2017)
DOI：: 10.1016/j.ces.2016.10.012

摘要：

我们已经进行了实验室实验来模拟地幔对流中羽流的重要方面。我们专注于确定羽流结构和动力学的粘度比U（周围流体和羽流流体之间）的作用。在我们的实验中，我们能够捕捉到地球物理对流制度相关的地幔对流的热点（当U > 1）和板块俯冲（当U < 1）制度。平面激光诱导荧光（PLIF）技术用于流动可视化和表征羽流结构。对流由较轻流体灌注穿过可渗透网产生的组成浮力驱动，并且粘度比U在1/300至2500的范围内系统地变化。在U=1的底部边界附近的平面形状，表现出一个著名的树枝状线羽状结构。随着U值的增加，观察到从树枝状羽流结构到离散球形羽流的渐进形态过渡，伴随着羽流的增厚和羽流间距的增加。在垂直剖面上，U=1时的蘑菇状地幔柱头部在高U时转变为断续的球状地幔柱，类似于地幔对流中的地幔柱热点。相反，对于低U值（~1/300），该机制对应于地幔中板块的俯冲。在这一制度中，我们观察到的第一次，羽流产生的厚边界细胞结构和发展成片状羽流。我们使用实验数据来量化这些形态的变化和混合动力学的羽流在不同制度的美国。我们还比较了我们的观察羽间距与文献中报道的各种模型，通过改变粘度比和浮力通量。

英文摘要：

We have conducted laboratory experiments to model important aspects of plumes in mantle convection. We focus on the role of the viscosity ratio U (between the ambient fluid and the plume fluid) in determining the plume structure and dynamics. In our experiments, we are able to capture geophysical convection regimes relevant to mantle convection both for hot spots (when U > 1) and plate-subduction (when U < 1) regimes. The planar laser induced fluorescence (PLIF) technique is used for flow visualization and characterizing the plume structures. The convection is driven by compositional buoyancy generated by the perfusion of lighter fluid across a permeable mesh and the viscosity ratio U is systematically varied over a range from 1/300 to 2500. The planform, near the bottom boundary for U=1, exhibits a well-known dendritic line plume structure. As the value of U is increased, a progressive morphological transition is observed from the dendritic-plume structure to discrete spherical plumes, accompanied with thickening of the plumes and an increase in the plume spacing. In the vertical section, mushroom-shaped plume heads at U=1 change into intermittent spherical-blob shaped plumes at high U, resembling mantle plume hot spots in mantle convection. In contrast, for low values of U (~1/300), the regime corresponds to subduction of plates in the mantle. In this regime, we observe for the first time that plumes arise from a thick boundary with cellular structure and develop into sheet-plumes. We use experimental data to quantify these morphological changes and mixing dynamics of the plumes at different regimes of U. We also compare our observations on plume spacing with various models reported in the literature by varying the viscosity ratio and the buoyancy flux.

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英文摘要：

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