Rotation Rate of Rods in Turbulence

PLEASE NOTE: This is a WEBINAR

The transport of particulate material by fluid flow is a problem with far reaching applications. Isotropic particles that are very small and neutrally buoyant behave as Lagrangian tracers and move with the local fluid velocity. However, particles that are large or density mismatched compared to the fluid have different dynamics from the local fluid. The rotational dynamics of anisotropic particles is different from spherical tracers and this fascinating problem is central for many applications ranging from cellulose fibers in paper making to dynamics of ice crystals in clouds. I study the dynamics of single rod-like particle in a turbulent flow between oscillating grids. The position and orientation of rods are measured experimentally using Lagrangian particle tracking with multiple high speed cameras. Rods rotate due to the velocity gradient of the flow and as tracer rods are transported by the flow their orientation becomes correlated with the velocity gradient tensor. This alignment results in suppression of the rotation rates of rods. We have also studied the effects of finite length of rods on the rotation rate in turbulence. As the length of the rods increases the rotation rate variance decreases. In the inertial range the Kolmogorov cascade argument describes the rotation rate of long rods.