Flexible Fibers in Turbulence

In this article, we review recent progress in the fundamental understanding of the motion of flexible fibers in a turbulent flow, made through multiscale experiments and simulations. Emphasis is given to problems involving flexible fibers that can be conveniently described with discrete and continuum models closely related to the slender body theory. Current state-of-the-art measurement and simulation methods, including optical techniques, Euler–Lagrange approaches for tracking large swarms of fibers, and recent methodologies for simulating finite-size fibers, are discussed. The capabilities of simulations and experiments are surveyed in connection with the current physical understanding of how flexible fibers interact with the full spectrum of length scales and timescales of turbulence. We review the phenomenological and statistical features of fiber dispersion and spatial distribution. We also discuss the relevant aspects of fiber rotation and deformation, highlighting their connection with mechanisms such as fragmentation and turbulence modulation, which are known to exhibit peculiar features in the case of flexible fibers. We conclude our analysis by providing an outlook on future research direction paths, open methodological issues, and expected advances, in particular those associated with the study of flexible particles in a broader sense.