Turbulence modulation by slender fibers in a channel flow

We numerically investigate the turbulence modulation by slender fibers in a turbulent channel flow at shear Reynolds number 300. Our Euler-Lagrangian approach is based on a Direct Numerical Simulation of the flow combined to the rod-chain pointwise representation of flexible fibers (Dotto et al., 2020) together with the ERPP method to account for the momentum exchange between the two phases (Battista et al., 2019). Such an investigation is enabled by a novel algorithm that makes the resolution of dispersed systems of constraint equations (representing the fibers) compatible with a state of the art, GPU-accelerated flow solver. We report a statistical analysis of the interaction between fibers and the flow at moderate concentration phi = 10^(-4), for slender particles of aspect ratio r=100 and dimensionless length L+ = 35 in wall units, which extends up to the inertial range of the turbulent scales. Turbulence modulation is reported for both tracer-like and almost neutrally buoyant fibers, characterized by Stokes number St=0.05, and inertial heavy fibers, characterized by Stokes number St=5, allowing us to focus on the influence of particle inertia on drag reduction (Gillissen et al., 2007; Wang et al., 2021).