Mearuring the orientation and roation rate of 3D printed particles in turbulence

Abstract

The orientation distribution and rotations of anisotropic particles in turbulent flows play a key role in many applications ranging from icy clouds to papermaking and drag reduction in pipe flow. However, experimental access to time-resolved orientations of anisotropic particles has not been easy to achieve. The use of 3D printing opens up the possibility to fabricate a wide range of particle shapes with smallest dimension down to 300 μm. So far, we have printed rods, crosses, jacks, triads, tetrads and helical particle shapes. We extract particle orientations from stereoscopic video images using a method of least squares optimization in Euler angle space. We find that in turbulence, the orientation and rotation-rate of many particles can be understood using a simple picture of alignment of both the vorticity and a long axis of the particle with the Lagrangian stretching direction of the flow.