# Revisiting the amplitude modulation in wall-bounded turbulence: towards a robust definition

## TL;DR

This study critically examines the robustness of amplitude modulation quantification in wall-bounded turbulence using LES data, comparing filtering methods, testing false positives, and analyzing structural inclination effects.

## Contribution

It introduces a comprehensive comparison of filtering techniques and assesses the influence of structural inclination on amplitude modulation measurement in turbulence.

## Key findings

- Fourier and EMD filters yield comparable results for amplitude modulation.
- False positives can occur with random signals, highlighting the need for careful analysis.
- Inclination angle significantly affects the quantification of amplitude modulation.

## Abstract

The present study revisits the amplitude modulation phenomenon, specifically for the robustness in its quantification. To achieve this, a well-resolved large-eddy simulation (LES) data set at Re_theta= 8200 is used. First, the fluctuating streamwise velocity signal is decomposed into its small- and large-scale components using both Fourier filters and empirical mode decomposition (EMD), allowing the comparison among different separation filters. The effects of these filters on various definitions for quantifying the amplitude modulation have been discussed. False positive identification of the amplitude modulation has also been tested using a randomised signal. Finally, the impact of the inclination angle of the large-scale structures on the modulation quantification has been assessed.