Jiang Hechuan, Wang Dongpu, Liu Shuang, Sun Chao
Center for Combustion Energy, Key Laboratory for Thermal Science and Power Engineering of MoE, and Department of Energy and Power Engineering, Tsinghua University, 100084 Beijing, China.
Huaneng Clean Energy Research Institute, 102209 Beijing, People's Republic of China.
Phys Rev Lett. 2022 Nov 11;129(20):204502. doi: 10.1103/PhysRevLett.129.204502.
What is the final state of turbulence when the driving parameter approaches infinity? For the traditional Rayleigh-Bénard convection, a possible ultimate scaling dependence of the heat transport (quantified by the Nusselt number Nu) on the Rayleigh number (Ra), which can be extrapolated to arbitrarily high Ra, is predicted by theories. The existence of the ultimate scaling has been intensively debated in the past decades. In this Letter, we adopt a novel supergravitational thermal convection experimental setup to study the possible transition to the ultimate regime. This system is characterized by the combined effects of radial-dependent centrifugal force, the Earth's gravity, and the Coriolis force. With an effective gravity up to 100 times the Earth's gravity, both Ra and shear Reynolds number can be boosted due to the increase of the buoyancy driving and the additional Coriolis forces. With over a decade of Ra range, we demonstrate the existence of ultimate regime with four direct evidences: the ultimate scaling dependence of Nu versus Ra; the appearance of the turbulent velocity boundary layer profile; the enhanced strength of the shear Reynolds number; and the new statistical properties of local temperature fluctuations. The present findings will greatly improve the understanding of the flow dynamics in geophysical and astrophysical flows.
当驱动参数趋于无穷大时，湍流的最终状态是什么？对于传统的瑞利 - 贝纳德对流，理论预测了热传输（由努塞尔数Nu量化）对瑞利数（Ra）的一种可能的最终标度依赖关系，这种关系可以外推到任意高的Ra。在过去几十年里，最终标度的存在一直存在激烈的争论。在本信函中，我们采用一种新型的超引力热对流实验装置来研究向最终状态的可能转变。该系统的特征在于径向依赖的离心力、地球引力和科里奥利力的综合作用。由于浮力驱动的增加和额外的科里奥利力，有效重力可达地球重力的100倍，从而可以提高Ra和剪切雷诺数。在超过十年的Ra范围内，我们通过四个直接证据证明了最终状态的存在：Nu对Ra的最终标度依赖关系；湍流速度边界层剖面的出现；剪切雷诺数强度的增强；以及局部温度波动的新统计特性。目前的研究结果将极大地增进对地球物理和天体物理流动中流体动力学的理解。
