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

• Digital holographic particle tracking velocimetry (DHPTV) is applied to measure 2D rotation.
• DHPTV measures irregular particle shape, 3D position and velocity, and 2D rotation simultaneously.
• Irregular coal particle and sprayed deformable ellipsoids are measured by DHPTV.

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 (20 r/s to 500 r/s) and nonspherical droplet ellipsoids (up to 200 r/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.

Particle morphology, 3D position and 3D translational velocity, and 2D rotation at different times. Note that the colors of the vector and filled particle area are proportional to the translational and rotational velocities, respectively. The arc color in side filled areas denotes the rotation direction, red: counterclockwise rotation, green: clockwise rotation.Figure optionsDownload as PowerPoint slide