Microfiber behavior in turbulence and in quiescent conditions: insights from 3D high-speed measurements

This research endeavors to enhance our understanding of the settling motions of microplastics in turbulence and in quiescent conditions. The scientific pursuit is fueled by the burgeoning environmental concern surrounding microplastics and the imperative need to refine predictive models for their behavior in different airflow conditions. Notably, existing drag models fall short in accurately predicting the settling velocities of microplastic fibers. The main goal of this study is to examine the settling dynamics of microfibers, particularly those with high aspect ratios. These microfibers are characterized by long, anisotropic (curved) geometries, with diameters ranging from 10 to 100 micrometers and lengths between 1 and 5 mm.    The challenge lies in accurately measuring their trajectories and rotational rates during gravitational settling, both in a static environment and within controlled isotropic turbulence (Re_lambda=250). The integration of six high-speed cameras enables the three dimensional reconstruction of the time-resolved orientation of each fiber, providing velocity and rotational rate along their trajectories. The in-house tracking procedure is described in detail in Alipour et al. (2021) and Giurgiu et al. (2023) for water channel applications. In the present work, we showcase the applicability of this measurement technique in airflow scenarios, unveiling the intricate dynamics of microfiber-turbulence interactions and the gravitational settling of slender microplastic fibers in atmosphere.   References: Alipour, M., De Paoli, M., Ghaemi, S., & Soldati, A. (2021). Long non-axisymmetric fibres in turbulent channel flow. Journal of Fluid Mechanics, 916, A3 Giurgiu, V., Caridi, G. C. A., Alipour, M., De Paoli, M., & Soldati, A. (2023). The TU Wien Turbulent Water Channel: Flow control loop and three-dimensional reconstruction of anisotropic particle dynamics. Review of Scientific Instruments, 94(9).