Kinematics and dynamics of freely rising spheroids at high Reynolds numbers

Abstract

Abstract

Wake induced dynamics of buoyancy-driven and anisotropic particles

“…Moreover, there is a longstanding notion [20], with mention already by Newton [9], that high levels of ⇠ 3 are associated with large path amplitudes0/⇡. This is clearly at odds with our results for > 1 (but also with findings by others [33,36,62,74]), where ⇠ 3 remains low even though0/⇡ is significant. Our analysis suggests that ⇠ 3 is instead more closely related to particle rotations.…”

“…From the raw data for the trajectories we then determined the dominant frequency of oscillation by considering the horizontal velocity signals. This result is then used to determine the centre-line of the trajectory indicated by the blue curves in figures 2.3 (a, b) [62]. The amplitude of the path oscillations (0) is based on the distance between the trajectory and its centre-line, i.e.…”

“…The metal ball was seated inside the shell and the halves are glued together and sanded to a smooth surface finish. The particle was then painted using the patterns identical to those used in [61,62], see Fig. 1.1(a), in order to enable accurate rotational tracking.…”

“…Particles, ⇡ = 12-25 mm, were released to settle or rise in a large vertical water tank. After an initial transient (> 20⇡), the position and orientation of the spheres were tracked over a distance of ⇡ 30-80⇡ using optical methods [61,62]. Two separate experimental setups were used in this work, one for rising and one for settling particles (Fig.…”

“…This is most evident in the spread of reported ⇠ 3 values (see figure 2.4 (b) and the corresponding discussion), but also manifests in di erences in the reported rise modes. Whereas [20] reported only planar ('zigzaging') trajectories, other studies find helical or spiralling motions [17,33,39,62,81] for comparable values of the parameters. Also the 'rectilinear mode' described in [20] for > 2A8C , in which particles rise straight without path oscillations is not observed consistently elsewhere; e.g.…”