Rotation rate of fibers in turbulence*

Since the last decade , more and more studies are devoted to the dynamics of anisotropic particles in turbulence. It has been shown theoretically and numerically that fibers smaller than the Kolmogorov length tend to align preferentially with the vorticity. More recently, Pujara et al. shows that longer fibers tend to align with the most extensional direction of the coarse grained velocity greadient. This difference of preferential alignment should have major impact on the rotational dynamics of particles: small fibers are expected to spin whereas long fibers are expected to tumble. We present here an experimental investigation on the global rotational dynamics (tumbling and spinning) of fibers smaller and larger than the Kolmogorov length. In this talk we will quantify the spinning and tumbling of fibers smaller and longer than the Kolmogorov length