Coherent structures in wall-bounded turbulence

Abstract

The inherent difficulty of understanding turbulence has led to researchers attacking the topic in many different ways over the years of turbulence research. Some approaches have been more successful than others, but most only deal with part of the problem. One approach that has seen reasonable success (or at least popularity) is that of attempting to deconstruct the complex and disorganised turbulent flow field into to a set of motions that are in some way organised. These motions are generally called "coherent structures". There are several strands to this approach, from identifying the coherent structures within the flow, defining their characteristics, explaining how they are created, sustained and destroyed, to utilising their features to model the turbulent flow. This review considers research on coherent structures in wallbounded turbulent flows: a class of flow which is extremely interesting to many scientists (mainly, but not exclusively, physicists and engineers) due to their prevalence in nature, industry and everyday life. This area has seen a lot of activity, particularly in recent years, much of which has been driven by advances in experimental and computational techniques. However, several ideas, developed many years ago based on flow visualisation and intuition, are still both informative and relevant. Indeed, much of the more recent research is firmly indebted to some of the early pioneers of the coherent structures approach. Therefore, in this review, selected historical research is discussed along with the more contemporary advances in an attempt to provide the reader with a good overview of how the field has developed and to highlight the perspicacity of some of the early researchers, as well as providing an overview of our current understanding of the role of coherent structures in wall-bounded turbulent flows.

Direct numerical simulation of a straight vortex tube in a laminar boundary-layer flow

“…Since the work of Theodorsen [40], there have been many studies on hairpin/horseshoe vortices. Several publications provide overviews of the formation of the hairpin vortex [31,2,19,8]. A typical symmetric hairpin vortex, which is shown in Fig.…”

Darcy-Weisbach resistance coefficient determination using Newton-Raphson approach for android 4.0

“…Newton-Raphson method optimizes the Newton point integration method by defining a more robust convergence equation. Convergence will exist if the difference of absolute value of calculated values in two successive iterations decreases while the number of iterations (n) increases (Quinta & Villalobos, 2005). The algorithm has been generalized in numerous forms to solve non-linear problems, equation systems, non-linear differential, and integral equations (Díaz & Benítez, 1998).…”

“…Turbulent flow may be defined as a vectoral chaos; in it we find continuous mixture conditions, due to vortex rupture. (Sotelo, 1997). Despite this widely observed phenomenon, recent studies have found vortex behavioral patterns in turbulent systems, which may defy the paradigms of turbulence according to current notions.…”

“…In fact, tests to model disorganized and complex turbulent flow conditions into series of somehow organized movement patterns, known as "coherent structures", have been made with mixed results. (Dennis, 2015).…”

“…On the other hand, heuristic tools lead to appropriation of knowledge by means of experimentation and autonomous discovering. Synergies between both algorithmic and heuristic tools produce the intelligent tutorial systems development (Galvis A., 1992).…”