Orientations of High-Concentration Fibers in Turbulence

The alignment of anisotropic particles in fluids has proven to be both practically important and visually striking, such as in rheoscopic fluids used in experimental observation and visual art pieces (the Kalliroscope). At high concentrations, particle orientations approach a continuous field whose ordering may be dominated by particle–particle interactions, as in liquid crystals or active matter, but it may instead reflect an underlying orientational order in the flow itself. We study the orientation field of fibers in turbulent flows both experimentally and in numerical simulations. In a turbulent flow, stiff fibers usually align with their neighbors, tending toward local order. However, the orientation field develops thin regions with large gradient, and a fractal geometry. This yields an anomalous scaling in the orientation structure functions at small separations. We will also discuss our methods for tracking the three-dimensional positions and orientations of fibers at high concentration, using views from multiple high-speed video cameras.