Visibility analysis of boundary layer transition

TL;DR

This paper introduces a novel network-based visibility analysis method to identify the transition from laminar to turbulent flow in boundary layers using only streamwise velocity time-series, avoiding extensive data requirements.

Contribution

It presents a new approach that uses visibility graphs and network metrics to detect flow transition markers from simple velocity time-series data.

Findings

Effectively captures flow transition from laminar to turbulent states.

Identifies transition markers without needing full velocity field data.

Accounts for free-stream turbulence effects on boundary layer transition.

Abstract

We study the transition to turbulence in a flat plate boundary layer by means of visibility analysis of velocity time-series extracted across the flow domain. By taking into account the mutual visibility of sampled values, visibility graphs are constructed from each time series. The latter are, thus, transformed into a geometrical object, whose main features can be explored using measures typical of network science that provide a reduced order representation of the underlying flow properties. Using these metrics, we observe the evolution of the flow from laminarity to turbulence and the effects exerted by the free-stream turbulence. Different from other methods requiring an extensive amount of spatiotemporal data (e.g., full velocity field) or a set of parameters and thresholds arbitrarily chosen by the user, the present network-based approach is able to identify the onset markers for transition by means of the streamwise velocity time-series alone.