Department of Physics, The Chinese University of Hong Kong, Shatin, Hong Kong, China.
Phys Rev Lett. 2015 Dec 31;115(26):264503. doi: 10.1103/PhysRevLett.115.264503. Epub 2015 Dec 30.
Coherent structures are ubiquitous in turbulent flows and play a key role in transport. The most important coherent structures in thermal turbulence are plumes. Despite being the primary heat carriers, the potential of manipulating thermal plumes to transport more heat has been overlooked so far. Unlike some other forms of energy transport, such as electromagnetic or sound waves, heat flow in fluids is generally difficult to manipulate, as it is associated with the random motion of molecules and atoms. Here we report how a simple geometrical confinement can lead to the condensation of elementary plumes. The result is the formation of highly coherent system-sized plumes and the emergence of a new regime of convective thermal turbulence characterized by universal temperature profiles and significantly enhanced heat transfer. It is also found that the universality of the temperature profiles and heat transport originate from the geometrical properties of the coherent structures, i.e., the thermal plumes. Therefore, in contrast to the classical regime, boundary layers in this plume-controlled regime are being controlled, rather than controlling.
相干结构在湍流中无处不在，对输运起着关键作用。热湍流中最重要的相干结构是羽流。尽管羽流是主要的热载体，但迄今为止，人们一直忽视了控制热羽流来输送更多热量的可能性。与电磁或声波等其他形式的能量传输不同，流体中的热流通常难以控制，因为它与分子和原子的随机运动有关。在这里，我们报告了简单的几何约束如何导致基本羽流的凝结。其结果是形成了高度相干的系统规模的羽流，并出现了一种新的对流热湍流模式，其特征是普遍的温度分布和显著增强的传热。还发现，温度分布和热传递的普遍性源于相干结构的几何特性，即热羽流。因此，与经典模式相比，在这种以羽流控制为主的模式中，边界层受到控制，而不是控制。
