Steering particles in turbulent flows

Particle shape is a primary design parameter used to control particle motion in fluid flows. When the flow is turbulent, the relative alignment between non-spherical particles and local flow structures plays a central role in particle motion. After introducing the ways particle shape couples to relative velocity, relative rotation, and local velocity gradients, this talk will explore how we design particles that will respond in desired ways in turbulence experiments. Elongated particles align with the local stretching direction which aligns with vorticity due to vortex stretching. If rod shaped particles have chiral ends with opposite handedness, they show a preferential rotation direction in particle coordinates. Ramified particles made of symmetric configurations of slender arms allow separate control over particle size and sedimentation rate. When sedimenting, particles tend to align with a long axis horizontal due to inertial torques. Turbulence competes with this preferential alignment, so by controlling particle shape, size, and sedimentation rate, one can control the orientation distribution and hence the lateral spreading rate.