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Experimental investigation of the structure of plane turbulent wall jets. Part 2. Structural analysis

Published online by Cambridge University Press:  29 April 2026

Harish Choudhary
Affiliation:
Mission Mausam (Weather Modification), Indian Institute of Tropical Meteorology (Ministry of Earth Sciences), Pashan, Pune 411008, India Department of Atmospheric and Space Sciences, Savitribai Phule Pune University, Pune, India
Abhishek Gupta
Affiliation:
Mission Mausam (Weather Modification), Indian Institute of Tropical Meteorology (Ministry of Earth Sciences), Pashan, Pune 411008, India
Shibani Bhatt
Affiliation:
Mission Mausam (Weather Modification), Indian Institute of Tropical Meteorology (Ministry of Earth Sciences), Pashan, Pune 411008, India
Thara Prabhakaran
Affiliation:
Mission Mausam (Weather Modification), Indian Institute of Tropical Meteorology (Ministry of Earth Sciences), Pashan, Pune 411008, India
Anandakumar Karipot
Affiliation:
Department of Atmospheric and Space Sciences, Savitribai Phule Pune University, Pune, India
Shivsai Ajit Dixit*
Affiliation:
Mission Mausam (Weather Modification), Indian Institute of Tropical Meteorology (Ministry of Earth Sciences), Pashan, Pune 411008, India Academy of Scientific and Innovative Research (AcSIR), Ghaziabad 201002, India
*
Corresponding author: Shivsai Ajit Dixit, sadixit@tropmet.res.in

Abstract

Building on the hypothesis of wall and jet structural modes proposed in Part 1 (Choudhary et al. 2024), this study reports coherent patterns and vortical structures associated with the jet mode by further analysing our experimental particle image velocimetry datasets. Instantaneous velocity fields are binned based on dominant streamwise Fourier modes, focusing on submodes with wavelengths $\lambda _x\approx 5{z_{T}}$ (submode 1) and $\lambda _x\approx 2.5{z_{T}}$ (submode 2); $z_{T}$ is outer length scale of the flow. Two-point correlations of streamwise velocity fluctuations for the total and modal fields reveal near-periodic coherent patterns inclined backwards (∼$14^{\circ }$) in the outer region and forwards (∼$9^{\circ }$) in the inner region. Vortical structures in conditionally averaged velocity fluctuation vector fields are examined using linear stochastic estimation (LSE) with anticlockwise vorticity (prograde) at the outer energy site as the condition. The vortical structure of submode 1 is a three-vortex system with (i) a robust clockwise vortex in the inner region and (ii) a saddle-point topology in the outer region. The vortical structure of submode 2 is a backward-leaning vortex packet. The LSE fields indicate Q1–Q3 events in the inner region contributed by ‘non-local’ eddies through the interaction of outer and inner submode 1 vortices. Quadrant analysis reveals that Q1–Q3 events due to ‘non-local’ eddies outweigh Q2–Q4 contributions of ‘local’ eddies, producing counter-gradient momentum diffusion below mean velocity maximum. These findings further substantiate the hypothesis of wall and jet structural modes and indicate that the region below mean velocity maximum in wall jets significantly differs from a turbulent boundary layer.

Information

Type
JFM Papers
Copyright
© The Author(s), 2026. Published by Cambridge University Press

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