Large-scale structures of scalar and velocity in a turbulent jet flow

Journal article (2021)

Authors

J. Reijtenbagh Fluid Mechanics - Mechanical, Maritime and Materials Engineering
J. Westerweel Fluid Mechanics - Mechanical, Maritime and Materials Engineering
W. van de Water Fluid Mechanics - Mechanical, Maritime and Materials Engineering
Research Group
Fluid Mechanics (Mechanical, Maritime and Materials Engineering) (TU Delft)
Copyright: © 2021 J. Reijtenbagh, J. Westerweel, W. van de Water
DOI: https://doi.org/10.1103/PhysRevFluids.6.084611
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Published Date

2021

Language

English

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Faculty

Mechanical, Maritime and Materials Engineering

Department

Process and Energy

Research Group

Fluid Mechanics

Abstract

We study the relation between large-scale structures in the concentration field with those in the velocity field in a dye-seeded turbulent jet. The scalar concentration in a plane is measured using laser-induced fluorescence. Uniform concentration zones of an advected scalar are indentified using cluster analysis. We simultaneously measure the two-dimensional velocity field using particle image velocimetry. The structures in the velocity field are characterized by finite-time Lyapunov exponents. The measurement of the scalar- and velocity fields moves with the mean flow. In this moving frame, turbulent structures remain in focus long enough to observe well-defined ridges of the finite-time Lyapunov field. This field gauges the rate of point separation along Lagrangian trajectories; it was measured both for future and past times since the instant of observation. The edges of uniform concentration zones are correlated with the ridges of the past-time Lyapunov field, but not with those of the future-time Lyapunov field. We quantify this relation using both conditional averages and the ordinary correlation function.