Heavy flexible fibers in turbulent channel flows*

Turbulent suspensions of long, slender fibers have wide-ranging applications in industry and nature, more evidently in the form of microplastics that plague our atmosphere and marine ecosystems. A large body of literature exists on the dynamics of flexible fibers whose densities are in the same order as that of the suspending fluid, as would be the case for most marine microplastics. However, relatively little attention has been given to the heavy fibers possessing large density ratios suspended in turbulence, akin to microplastics in the atmosphere. On account of this, we study the dynamics of flexible fibers possessing large density ratios of the order 10² to 10³ with respect to the fluid, suspended in a turbulent channel flow with shear Reynolds numbers Re_τ = 300 and 600. We subsequently investigate the combined role of fiber length, flexibility, and particle and fluid inertia on the collective dynamics of fibers by means of performing direct numerical Euler-Lagrange simulations.