TURBULENT 3-D THERMAL-CONVECTION IN AN INFINITE PRANDTL NUMBER, VOLUMETRICALLY HEATED FLUID - IMPLICATIONS FOR MANTLE DYNAMICS
TURBULENT 3-D THERMAL-CONVECTION IN AN INFINITE PRANDTL NUMBER, VOLUMETRICALLY HEATED FLUID - IMPLICATIONS FOR MANTLE DYNAMICS
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DOI：
10.1111/j.1365-246x.1994.tb01795.x
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发表时间：
1994-02-01
影响因子：
2.8
通讯作者：
TRAVIS, BJ
中科院分区：
文献类型：
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作者：
PARMENTIER, EM;SOTIN, C;TRAVIS, BJ
研究了体积加热的无限普朗特数流体中三维热对流的结构和时间依赖性。所采用的方法允许数值实验进行足够长的时间，以获得对结构的平均和波动部分的良好估计。用迭代多刚体法求解能量方程中每个时间步长的浮力不可压缩粘性流是该方法的一个新方面。利用能量方程的简单显式时间步长，在串行计算机上矢量化良好，非常适合大规模并行计算机。在规定温度的上边界和绝热的下边界条件下，对3 × 10(6) ~ 3 × 10(7)的瑞利数进行了数值实验。在瑞利数的整个范围内，流动结构主要由冷的、几乎轴对称的羽流组成，这些羽流水平迁移，横扫对流流体顶部形成的冷热边界层。羽流与其他羽流合并而消失；新的羽流是由热边界层的不稳定性产生的。片状羽流只是偶尔形成，在流体中不会穿透到很深的地方。羽流的大小与热边界层的厚度相当，平均间距与流体深度相当。流体中没有持续的大规模运动。它的缺失可能反映了当冷羽流穿透到底边界而没有与周围流体热平衡时，热边界层下形成的大的亚绝热分层。我们考虑了行星地幔对流和板块构造存在的可能含义。
The structure and time dependence of 3-D thermal convection in a volumetrically heated, infinite Prandtl number fluid is examined for high values of the Rayleigh number. The methods employed allow the numerical experiments to proceed for long-enough times to derive good estimates of mean and fluctuating parts of the structure. An iterative multirigid method to solve for the buoyant, incompressible viscous flow at each time step of the energy equation is a novel aspect of the methodology. A simple explicit time step of the energy equation is utilized that vectorizes well on serial computers and which is ideally suited to massively parallel computers. Numerical experiments were carried out for Rayleigh numbers from 3 x 10(6) to 3 x 10(7) in a cartesian region with a prescribed temperature at the top boundary and an adiabatic bottom boundary. Over this complete range of Rayleigh number, the flow structure consists dominantly of cold, nearly axisymmetric plumes that migrate horizontally sweeping off the cold thermal-boundary layer that forms at the top of the convecting fluid. Plumes disappear by coalescing with other plumes; new plumes are created by thermal-boundary-layer instability. Sheet plumes form only occasionally and do not penetrate to significant depths in the fluid. Plumes have sizes comparable to the thickness of the thermal-boundary layer and an average spacing comparable to the fluid depth. No persistent large-scale motion in the fluid can be identified. Its absence may reflect the large subadiabatic stratification that develops beneath the thermal-boundary layer as cold plumes penetrate to the bottom boundary without thermally equilibrating with surrounding fluid. We consider the possible implications for convection in planetary mantles and for the existence of plate tectonics.