Visibility graph analysis of wall turbulence time-series

Giovanni Iacobello,Stefania Scarsoglio,Luca Ridolfi

doi:10.1016/j.physleta.2017.10.027

Giovanni Iacobello, Stefania Scarsoglio + Show 1 more

Open Access

https://doi.org/10.1016/j.physleta.2017.10.027

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Journal: Physics Letters A	Publication Date: Oct 18, 2017
Citations: 43	License type: cc-by

Affiliation: Polytechnic University of Turin

Abstract

The spatio-temporal features of the velocity field of a fully-developed turbulent channel flow are investigated through the natural visibility graph (NVG) method, which is able to fully map the intrinsic structure of the time-series into complex networks. Time-series of the three velocity components, (u,v,w), are analyzed at fixed grid-points of the whole three-dimensional domain. Each time-series was mapped into a network by means of the NVG algorithm, so that each network corresponds to a grid-point of the simulation. The degree centrality, the transitivity and the here proposed mean link-length were evaluated as indicators of the global visibility, inter-visibility, and mean temporal distance among nodes, respectively. The metrics were averaged along the directions of homogeneity (x,z) of the flow, so they only depend on the wall-normal coordinate, y+. The visibility-based networks, inheriting the flow field features, unveil key temporal properties of the turbulent time-series and their changes moving along y+. Although intrinsically simple to be implemented, the visibility graph-based approach offers a promising and effective support to the classical methods for accurate time-series analyses of inhomogeneous turbulent flows.

Highlights

One of the most challenging research topic in classical physics is represented by turbulent flows
The procedure described in the previous section is adopted to analyze the velocity time-series of the turbulent channel flow, starting from the streamwise component, u∗, and considering the other velocity components, v∗ and w∗
The global network-metrics { k ; T r; d1n }, computed for each of the Sx × Sz grid-point, have regular trends similar to the averaged ones shown in Fig. 3, which are representative of the global metrics measured along the wall-normal direction and in different (x, z) coordinates

Summary

Introduction

One of the most challenging research topic in classical physics is represented by turbulent flows. Their great importance is evident through a number of natural phenomena (e.g., rivers, atmospheric and oceanic streams), industrial and civil applications (e.g., flow through pumps, heat exchangers, wake flows of vehicles and aircraft, wind-building interactions) in which turbulence is involved. The study of wall-bounded turbulent flows, in particular, is a very active research field, due to the great attention paid to the fluid-structure interaction. Deeply studied from a phenomenological and theoretical point of view, the turbulence dynamics, due to their complexity, are still not fully understood [1, 2]. Mainly relying on statistical techniques, are typically used to explore and analyze turbulent flows

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