Interfacial turbulence in falling liquid films

降膜是一种对流不稳定的开放流流体动力系统，具有丰富的空间/时间结构和一系列波不稳定性和过渡，这对于一大类流体动力系统和其他非线性系统是通用的：入口处的白色噪声，线性不稳定的过滤机制，二次调制，将一次波场转换为二维波场（2D - 1+1维）孤立脉冲，并最终过渡的2D脉冲到一个充分发展的三维（3D - 2+1维）波制度。这一发展阶段通常被称为“界面相容性”。这是低维时空混沌或“弱/耗散的连续性”：事实上，尽管系统的明显复杂性，人们仍然可以识别3D孤立脉冲在什么似乎是一个随机扰动的表面。然后，3D脉冲变成基本过程，因此电影的动态可以被描述为这些脉冲的叠加。因此，降液膜可以作为弱/耗散湍流研究的规范参考系。除了纯理论的兴趣之外，降液膜在开发各种工程和技术应用中的有效传热和传质手段方面发挥着核心作用，例如蒸发器，换热器，吸收器，洗涤器，精馏塔，结晶器和降膜反应器。这主要是由于在相对小的流速下降膜的小的传热和传质阻力。这种阻力进一步降低的2D/3D孤立脉冲的存在下，在自由表面的膜前面提到的，这通常会导致显着增强的传热和masstransfer.Not令人惊讶，因此，下降液膜一直是基础和应用研究的主题几十年。然而，尽管有几个发展和相当大的关注，波的演化的降膜已经收到，大量的问题和问题还没有得到解决，特别是，三维孤立脉冲的相互作用和最终过渡到界面湍流，仍然逃避我们。为了回答这些问题，在这个项目的任期内所追求的研究领域涉及的理论发展的三维孤立脉冲的相干结构理论的下降膜的主要目的是促进我们的理解界面湍流。

A falling film is a convectively unstable open-flow hydrodynamic system with a rich variety of spatial/temporal structures and a sequence of wave instabilities and transitions which are generic to a large class of hydrodynamic and other nonlinear systems: white noise at the inlet, filtering mechanism of linear instability, secondary modulation that transforms the primary wave field into two-dimensional (2D -- 1+1 dimensions) solitary pulses and eventually transition of the 2D pulses into a fully developed three-dimensional (3D -- 2+1 dimensions) wave regime. This stage of the evolution is frequently referred to as `interfacial turbulence'. This is low-dimensional spatio-temporal chaos or alternatively `weak/dissipative turbulence': indeed, despite the apparent complexity of the system one can still identify 3D solitary pulses in what appears to be a randomly disturbed surface. 3D pulses then become elementary processes so that the dynamics of the film can be described as a superposition of these pulses. Hence, a falling liquid film can serve as a canonical reference system for the study of weak/dissipative turbulence.In addition to the purely theoretical interest, falling liquid films play a central role in the development of efficient means of heat and mass transfer in a wide variety of engineering and technological applications, such as evaporators, heat exchangers, absorbers, scrubbers, rectification columns, crystallizers and falling film reactors. This is mainly due to the small heat and mass transfer resistance of a falling film at relatively small flow rates. This resistance is further decreased by the presence of 2D/3D solitary pulses at the free surface of the film mentioned earlier which typically lead to a significant enhancement of heat and mass transfer.Not surprisingly, therefore, falling liquid films have been a topic of fundamental and applied research for several decades. However,despite the several developments and considerable attention that wave evolution on a falling film has received, a large number of issues and problems have not been resolved, and in particular, the interaction of 3D solitary pulses and eventual transition to interfacial turbulence, still elude us. In an attempt to answer these questions, the field of research to be pursued during the tenure of this project concerns the theoretical development of a coherent structures theory of 3D solitary pulses on a falling film with the principal aim to advance our understanding of interfacial turbulence.