Published November 5, 2026 | Version 1.0

Supporting Materials for "Airflow Velocity Estimation from a Fluttering Tuft"

Description

Airflow velocity measurement is essential for a wide range of applications, yet most quantitative techniques rely on expensive or complex instrumentation that restricts in-situ deployment. Tufts, passive filaments traditionally used as qualitative indicators of flow direction, have received comparatively little attention for quantitative velocity estimation. This paper presents a method for estimating airflow velocity magnitude from the temporal dynamics of a passive tuft. Time-resolved tuft-tip displacement signals are extracted by digital image processing from two synchronized camera views and mapped by an attention-based long short-term memory (LSTM) network to estimate the corresponding time-averaged velocity magnitude. Experimental evaluations under fixed-point, streamwise, spanwise, and two-dimensional field conditions in a turbulent jet flow showed that the method can accurately capture velocity variations, with median absolute percentage errors up to 4.4%. By exploiting the temporal dynamics of tuft motion, the proposed approach enables quantitative velocity magnitude estimation using a single, simple passive element, offering a foundation for further investigation of a low-cost, vision-based, and easy-to-implement airflow sensing method in open flow environments.

Notes (English)

Description of Supporting Materials

This repository provides supplementary figures, a supporting video, and numerical data associated with the study "Airflow Velocity Estimation from a Fluttering Tuft." The materials provide additional information on neural-network architecture comparisons, long-term measurement stability, and the statistical characteristics of the datasets used for model development and evaluation.

The repository contains the following files:

Supplementary figures

  • Fig. R1. Performance comparison of capacity-matched LSTM architectures.png: Compares the velocity estimation performance of LSTM architectures with different numbers of recurrent layers and an attention-based LSTM, using approximately matched numbers of trainable parameters.

  • Fig. R2. MFC feedback signals for tuft trials.png: Presents the mass flow controller (MFC) feedback signals recorded during two long-term tuft measurement trials.

  • Fig. R3. Evolution of signed percentage errors of tuft trials.png: Shows the temporal evolution of signed percentage errors in the tuft-based velocity estimates during the long-term measurement trials, providing information on estimation drift.

Supplementary tables

  • Table RI Architectural configurations of capacity-matched LSTM models.csv: Lists the architectural configurations of the compared LSTM models, including the number of recurrent layers, hidden units, attention dimensions, trainable parameters, and relative differences in parameter counts.

  • Table RII Statistics of input displacement and reference velocity.csv: Provides descriptive statistics (mean, standard deviation, minimum, and maximum) of the three-dimensional tuft-tip displacement components (x, y, and z) and reference airflow velocity for the training, validation, and testing datasets.

Supporting video

  • Supporting video.mp4: Provides a visual demonstration accompanying the proposed tuft-based airflow sensing method.

These materials are made publicly available to facilitate the interpretation of the reported results and support further analysis of the proposed airflow sensing method.

Files

Fig. R1. Performance comparison of capacity-matched LSTM architectures.png

Files (17.9 MB)