Bushuk Mitchell, Holland David M, Stanton Timothy P, Stern Alon, Gray Callum
Geophysical Fluid Dynamics Laboratory, NOAA, Princeton, New Jersey, 08540, USA.
Center for Atmosphere Ocean Science, Courant Institute of Mathematical Sciences, New York University, New York, NY, 10012, USA.
J Fluid Mech. 2019 Aug 25;873:942-976. doi: 10.1017/jfm.2019.398. Epub 2019 Jun 28.
Ice scallops are a small-scale (5-20cm) quasi-periodic ripple pattern that occurs at the ice-water interface. Previous work has suggested that scallops form due to a self-reinforcing interaction between an evolving ice-surface geometry, an adjacent turbulent flow field, and the resulting differential melt rates that occur along the interface. In this study, we perform a series of laboratory experiments in a refrigerated flume to quantitatively investigate the mechanisms of scallop formation and evolution in high resolution. Using particle-image velocimetry, we probe an evolving ice-water boundary layer at sub-millimeter scales and 15Hz frequency. Our data reveals three distinct regimes of ice-water interface evolution: A transition from flat to scalloped ice; an equilibrium scallop geometry; and an adjusting scallop interface. We find that scalloped ice geometry produces a clear modification to the ice-water boundary layer, characterized by a time-mean recirculating eddy feature that forms in the scallop trough. Our primary finding is that scallops form due to a self reinforcing feedback between the ice-interface geometry and shear production of turbulent kinetic energy in the flow interior. The length of this shear production zone is therefore hypothesized to set the scallop wavelength.
冰扇贝是出现在冰水界面的一种小规模（5 - 20厘米）准周期性波纹图案。先前的研究表明，扇贝的形成是由于不断演变的冰面几何形状、相邻的湍流场以及沿界面产生的差异融化速率之间的自增强相互作用。在本研究中，我们在冷藏水槽中进行了一系列实验室实验，以高分辨率定量研究扇贝形成和演变的机制。使用粒子图像测速技术，我们在亚毫米尺度和15赫兹频率下探测不断演变的冰水边界层。我们的数据揭示了冰水界面演变的三个不同阶段：从平坦冰到扇贝状冰的转变；平衡的扇贝几何形状；以及调整中的扇贝界面。我们发现，扇贝状冰的几何形状对冰水边界层产生了明显的改变，其特征是在扇贝槽中形成的时间平均再循环涡旋特征。我们的主要发现是，扇贝的形成是由于冰界面几何形状与流动内部湍动能的剪切产生之间的自增强反馈。因此，假设这个剪切产生区的长度决定了扇贝的波长。
