Topography generation by melting and freezing in a turbulent shear flow
Topography generation by melting and freezing in a turbulent shear flow
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DOI：
10.1017/jfm.2020.1064
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发表时间：
2021-02-01
影响因子：
3.7
通讯作者：
Jenkins, Adrian
中科院分区：
文献类型：
--
作者：
Couston, Louis-Alexandre;Hester, Eric;Jenkins, Adrian
我们报告了一项理想的数值研究，研究了在湍流、浮力影响的剪切流附近融化和冻结的固体，以提高我们对环境中相位变化产生地形的理解。我们用相场法将固体的热方程与流体的Navier-Stokes方程动态耦合。我们研究了一个最初平坦的水平固体边界的演变，覆盖在压力驱动的湍流上。我们假设流体的线性状态方程，并改变热膨胀系数的符号，使背景密度分层要么稳定，要么中性，要么不稳定。我们发现，与平均流动方向对齐的通道是由流固界面的相变自发产生的。流体中的流向涡、界面形貌和固体中的温度场相互影响和调整，直到获得统计稳态。在所有情况下，波峰到波谷的波幅都大于大约10个delta(nu)，其中delta（nu）是粘性长度尺度，但对于不稳定的分层，波峰到波谷的波幅要比中性或稳定的分层大得多，而且持续时间更长。这是因为稳定的分层使冷的熔体流体浮起，从而保护通道不进一步融化，而不稳定的分层使冷的熔体流体下沉，通过上升的热羽流诱导进一步融化。研究了流速和熔化率的统计数据，发现模拟中出现的通道和龙骨对平均阻力系数的影响并不显著。
We report an idealized numerical study of a melting and freezing solid adjacent to a turbulent, buoyancy-affected shear flow, in order to improve our understanding of topography generation by phase changes in the environment. We use the phase-field method to dynamically couple the heat equation for the solid with the Navier-Stokes equations for the fluid. We investigate the evolution of an initially flat and horizontal solid boundary overlying a pressure-driven turbulent flow. We assume a linear equation of state for the fluid and change the sign of the thermal expansion coefficient, such that the background density stratification is either stable, neutral or unstable. We find that channels aligned with the direction of the mean flow are generated spontaneously by phase changes at the fluid-solid interface. Streamwise vortices in the fluid, the interface topography and the temperature field in the solid influence each other and adjust until a statistical steady state is obtained. The crest-to-trough amplitude of the channels is larger than approximately 10 delta(nu) in all cases, with delta(nu) the viscous length scale, but is much larger and more persistent for an unstable stratification than for a neutral or stable stratification. This happens because a stable stratification makes the cool melt fluid buoyant such that it shields the channel from further melting, whereas an unstable stratification makes the cool melt fluid sink, inducing further melting by rising hot plumes. The statistics of flow velocities and melt rates are investigated, and we find that channels and keels emerging in our simulations do not significantly change the mean drag coefficient.