Measuring the effects of finite length of rods on rotation rate in turbulent flow

We study the rotational dynamics of single rod-like particles ranging from tracer rods to long rods and quantify the effects of length of rod on it's rotation rate in turbulent flow. The position and orientation of rods are measured experimentally using Lagrangian particle tracking with multiple cameras in a flow between oscillating grids. \newline The rotation rate of rods is determined by the velocity gradient of the flow. As rods are transported in the flow they develop alignment with the directions of the vorticity and eigenvectors of the strain-rate. This alignment results in a smaller rotation rate from randomly oriented rods. Tracer rods rotate due the velocity gradient of the smallest eddies that produce the largest shear rate while longer rods average over length-scales ranging from eddies smaller than their size to eddies order of their own length-scale. As the length of the rods increases the rotation rate variance gets smaller.