Long non-axisymmetric fibres in channel flow turbulence

Effect of shape asymmetry on the behavior of the long fibers is investigated in this study. The experimental facility consists of a closed water channel (aspect ratio 10). The fibers used are characterized by a length-to-diameter ratio of 120 and moderately curved. Fibers are recorded by four high-speed cameras in a fully developed flow section. We propose a new 3D reconstruction and tracking method based on the light intensity distribution, consisting of time-resolved multiple algebraic reconstruction technique (MART) combined with an advanced imaging analysis technique. With the experimental database produced, we are able to link the fibers dynamics to their shape, i.e. to the average fiber curvature. Fibers concentration, orientation and rotational dynamics are investigated all along the channel height, which includes the near-wall flow region. We observed that small deviations from the straight shape (i.e. small values of the fibers curvature) can produce significant modifications of fibers concentration and orientation. Moreover, from the analysis of the mean squared tumbling, we show that also the rotational dynamics of the fibers are controlled by their shape and the magnitude of the mean squared tumbling increases as a function of the shape asymmetry.