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تسجيل مستخدم جديدDynamics of freely rising spheres: the effect of moment of inertia
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The goal of this study is to elucidate the effect the particle moment of inertia (MOI) has on the dynamics of spherical particles rising in a quiescent and turbulent fluid. To this end, we performed experiments with varying density ratios $Gamma$, the ratio of the particle density and fluid density, ranging from $0.37$ up to $0.97$. At each $Gamma$ the MOI was varied by shifting mass between the shell and the center of the particle to vary $I^*$ (the particle MOI normalised by the MOI of particle with the same weight and a uniform mass distribution). Helical paths are observed for low, and `3D chaotic trajectories at higher values of $Gamma$. The present data suggests no influence of $I^*$ on the critical value for this transition $0.42<Gamma_{textrm{crit}}<0.52$. For the `3D chaotic rise mode we identify trends of decreasing particle drag coefficient ($C_d$) and amplitude of oscillation with increasing $I^*$. Due to limited data it remains unclear if a similar dependence exists in the helical regime as well. Path oscillations remain finite for all cases studied and no `rectilinear mode is encountered, which may be the consequence of allowing for a longer transient distance in the present compared to earlier work. Rotational dynamics did not vary significantly between quiescent and turbulent surroundings, indicating that these are predominantly wake driven.
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