Kinematics and dynamics of freely rising spheroids at high Reynolds numbers

We experimentally investigate the effect of geometrical anisotropy for buoyant ellipsoidal particles rising in a still fluid. All other parameters, such as Galileo number $Ga \approx 6000$ and particle density ratio $\Gamma 0.53$ are kept constant. The aspect ratio, $\chi$, is varied systematically from $\chi$ = 0.2 (oblate) to 5 (prolate). Based on tracking all degrees motion, we identify six regimes characterised by distinct rise dynamics. Firstly, $0.83 \le \chi 1.20$, increased rotational dynamics observed flips over semi-regularly "tumbling"-like motion. Secondly, oblate with $0.29 0.75$, planar regular "zig-zag" motion observed, where drag coefficient independent $\chi$. Thirdly, most extreme geometries ($\chi 0.25$) "flutter"-like behaviour found, precession oscillation plane an increase coefficient. For prolate geometries, two coexisting modes that contribute complex trajectories: first related oscillations pointing vector second corresponds perpendicular particle's symmetry axis. "longitudinal" regime ($1.33 2.5$), both active different one, "broadside"-regime ($3 \chi\le 4$), only mode present. Remarkably, 5$), observe entirely "helical" completely unique features.