Experimental Investigation of Compact Debris Flight in Highly Turbulent Winds

Abstract The wind fields that drive debris flight are highly turbulent due to both the inherent turbulence of the approaching flow and the additional turbulence generated by nearby buildings. The significant size disparity between debris and buildings makes consistent scaling in wind tunnel experiments particularly difficult and often requires large-scale tests (e.g., 1 ∶ 20 ). At such large scales, conventional boundary layer wind tunnel techniques suffer from a well-known limitation, a deficit of low-frequency turbulence energy. Due to these challenges, the existing wind tunnel experiments on windborne debris flight failed to simultaneously scale down the approaching turbulent flow, neighboring buildings, and debris. Although these experimental findings reflect the most advanced work to date, they may not faithfully represent real-world scenarios such as the complex urban environment as a result of these challenges. This study leverages recent advancements in wind tunnel testing capabilities to systematically investigate the effects of highly turbulent wind fields on compact debris flight. The building and debris sizes are carefully selected to replicate real-world conditions at a 1 ∶ 20 scale, where actively controlled fans are employed to mitigate the low-frequency turbulence deficit associated with large geometric scale. High-speed cameras combined with computer vision are used to track the three-dimensional flight trajectories of spherical debris within this complex wind environment. The experimental results reveal that (1) incorporating low-frequency turbulence to address the typical low-frequency energy deficit in large-scale experiments and thereby achieve a full-scale representative spectrum significantly increases the variability of debris flight, and (2) the presence of a neighboring building effectively alters the local wind field (wind direction, mean wind speed, turbulence intensity, and spectra) and leads to debris flight characteristics that differ substantially from those observed in unobstructed flow. This study provides an archival data set for validating numerical models that simulates debris flight in complex wind conditions.