TY - JOUR
T1 - Kinematics and dynamics of freely rising spheroids at high Reynolds numbers
AU - Will, Jelle B.
AU - Mathai, Varghese
AU - Huisman, Sander G.
AU - Lohse, Detlef
AU - Sun, Chao
AU - Krug, Dominik
N1 - Cambridge UP deal
Publisher Copyright:
© 2021 The Author(s). Published by Cambridge University Press.
PY - 2021/4/10
Y1 - 2021/4/10
N2 - We experimentally investigate the effect of geometrical anisotropy for buoyant spheroidal particles rising in a still fluid. All other parameters, such as the Galileo number (the ratio of gravitational to viscous forces), the ratio of the particle to fluid density and the dimensionless moment of inertia (with being the moment of inertia of the particle and that of the fluid in an equivalent volume), are kept constant. The geometrical aspect ratio of the spheroids, is varied systematically from (oblate) to 5 (prolate). Based on tracking all degrees of particle motion, we identify six regimes characterised by distinct rise dynamics. Firstly, for, increased rotational dynamics are observed and the particle flips over semi-regularly in a 'tumbling'-like motion. Secondly, for oblate particles with, planar regular 'zig-zag' motion is observed, where the drag coefficient is independent of. Thirdly, for the most extreme oblate geometries (), a 'flutter'-like behaviour is found, characterised by precession of the oscillation plane and an increase in the drag coefficient. For prolate geometries, we observed two coexisting oscillation modes that contribute to complex trajectories: The first is related to oscillations of the pointing vector and the second corresponds to a motion perpendicular to the particle's symmetry axis. We identify a 'longitudinal' regime (), where both modes are active and a different one, the 'broadside'-regime (), where only the second mode is present. Remarkably, for the most prolate particles (), we observe an entirely different 'helical' rise with completely unique features.
AB - We experimentally investigate the effect of geometrical anisotropy for buoyant spheroidal particles rising in a still fluid. All other parameters, such as the Galileo number (the ratio of gravitational to viscous forces), the ratio of the particle to fluid density and the dimensionless moment of inertia (with being the moment of inertia of the particle and that of the fluid in an equivalent volume), are kept constant. The geometrical aspect ratio of the spheroids, is varied systematically from (oblate) to 5 (prolate). Based on tracking all degrees of particle motion, we identify six regimes characterised by distinct rise dynamics. Firstly, for, increased rotational dynamics are observed and the particle flips over semi-regularly in a 'tumbling'-like motion. Secondly, for oblate particles with, planar regular 'zig-zag' motion is observed, where the drag coefficient is independent of. Thirdly, for the most extreme oblate geometries (), a 'flutter'-like behaviour is found, characterised by precession of the oscillation plane and an increase in the drag coefficient. For prolate geometries, we observed two coexisting oscillation modes that contribute to complex trajectories: The first is related to oscillations of the pointing vector and the second corresponds to a motion perpendicular to the particle's symmetry axis. We identify a 'longitudinal' regime (), where both modes are active and a different one, the 'broadside'-regime (), where only the second mode is present. Remarkably, for the most prolate particles (), we observe an entirely different 'helical' rise with completely unique features.
KW - UT-Hybrid-D
KW - vortex shedding
KW - particle/fluid flow
KW - fluid flow
KW - particle
UR - http://www.scopus.com/inward/record.url?scp=85100790827&partnerID=8YFLogxK
U2 - 10.1017/jfm.2020.1104
DO - 10.1017/jfm.2020.1104
M3 - Article
AN - SCOPUS:85100790827
VL - 912
JO - Journal of fluid mechanics
JF - Journal of fluid mechanics
SN - 0022-1120
M1 - A16
ER -