DOI: 10.5258/soton/d3809
title: Dataset for Reynolds number effects on surface-induced secondary flows in turbulent boundary layers

description: ============================================================
'Dataset for Reynolds number effects on surface-induced secondary flows in turbulent boundary layers'
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Dataset DOI: 10.5258/soton/d3809

Date of data collection: 03/2023 – 06/2023 (original experiment) and 06/2024 (smooth-wall dataset)

Licence: CC-BY

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Associated publication
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This dataset presents the experimental data described in:

Medjnoun, T., Nilsson-Takeuchi, M. & Ganapathisubramani, B., "Reynolds number effects on surface-induced secondary flows in turbulent boundary layers", Journal of Fluid Mechanics, 2026.

Manuscript DOI: 10.1017/jfm.2026.11216

PLEASE REFER TO THE JOURNAL PAPER WHEN CITING OR USING THIS DATA.

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Overview
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The data provided here correspond to the post-processed
experimental measurements used to generate the figures
presented in the manuscript. All data are provided in MATLAB (.mat) format.

The dataset are made of three subsets. Using the data provided, together with the
normalisation parameters included in the files, the figures in the paper can be reproduced.

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File description and figure mapping
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1. Fig2_DragBalance.mat

This file contains the drag-balance measurements used to
evaluate the skin-friction coefficient and Reynolds-number
scaling presented in Figure 2.

The dataset includes the quantities required to compute the
skin-friction trends and to evaluate equation (3.1) in the
manuscript.

Main quantities include (variable names given in the file):
- Cf Skin-friction coefficient
- Rex Streamwise Reynolds number
- utau Friction velocity
- delta Boundary-layer thickness
- Re_tau Friction Reynolds number

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2. Fig3-12_HotWire_RoughWall.mat

This file contains the post-processed hot-wire anemometry data
for the rough-wall configurations (T50, T100, T200).

The data are sufficient to reproduce Figures 3–12, including:
- inner-scaled mean velocity profiles,
- velocity variance profiles,
- roughness-function trends,
- merging height and roughness height in wall units,
- pre-multiplied energy spectra,
- wavelength- and frequency-scaled spectral representations.

The data are stored in structured arrays indexed by:
- speed case
- surface geometry

Main quantities include:
- y, yplus Wall-normal coordinates
- mean_u, uplus Mean velocity profiles
- var_u Velocity variance
- Cf, utau Skin friction and friction velocity
- Re_tau, Re_theta Reynolds numbers
- Hplus, Lplus Roughness-related wall units
- Psdc Pre-multiplied energy spectra
- Fm, Wavek Frequency and wavelength coordinates
- delta, delta99 Boundary-layer thickness measures

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3. Fig3-12_HotWire_SmoothWall.mat

This file contains the smooth-wall hot-wire baseline data
used for reference and comparison with the rough-wall cases.

The variable naming convention and structure follow those
used in the rough-wall hot-wire dataset, where applicable,
to allow direct comparison.

Main quantities include:
- y, yplus Wall-normal coordinates
- mean_u, uplus Mean velocity profiles
- var_u Velocity variance
- Cf, utau Skin friction and friction velocity
- Re_tau, Re_theta Reynolds numbers
- Psdc Energy spectra
- Fm, Wavek Frequency and wavelength coordinates

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Notes on data usage
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- The data provided are post-processed results derived from
 the original experimental measurements.
- The datasets are intended to support figure reproduction,
 comparison, and further analysis.
- Raw hot-wire voltage signals and raw drag balance outputs
 are not included.