Simultaneous measurement of 3D velocity and 2D rotation of irregular particle with digital holographic particle tracking velocimetry

Abstract

The dispersed irregular particle can have a complicated both translational and rotational motions in multiphase flows, and the experimental evaluation of the interactions of a particle with its surrounding relies on the quantitative measurement methods. Digital inline holographic particle tracking velocimetry (DHPTV) is proposed to measure the projected morphology, 3D translational as well as 2D rotational (ωz) motion of an irregular particle simultaneously. In order to measure the particle rotation and translation in the double pulses/double frame DHPTV, the relation among the rotation speed, translational velocity and characteristic length of the particle is formulated. The rotation angle around z axis of the irregular particle in the two frames can be determined by pairing the feature points of the reconstructed in-focus particle images. The 2D rotations of an irregular coal particle in an acoustic levitator (20r/s to 500r/s) and nonspherical droplet ellipsoids (up to 200r/s) in a spray were measured. Results show that the recovered particle image from the second frame overlaps the original one in the first frame, evidencing the accurate particle rotation ωz measurements. This work demonstrates that DHPTV can measure the particle shape, 3D position and 3D velocity as well as 2D rotation simultaneously, which provides a tool to get a deeper understanding of particle dynamics in a multiphase flow.