Strong alignment of prolate ellipsoids in Taylor–Couette flow

We report on the mobility and orientation of finite-size, neutrally buoyant prolate ellipsoids (of aspect ratio $\Lambda=4$) in Taylor-Couette flow, using interface resolved numerical simulations. The setup consists a particle-laden flow between rotating inner stationary outer cylinder. simulate two particle sizes $\ell/d=0.1$ $\ell/d=0.2$, $\ell$ denoting major axis $d$ gap-width cylinders. volume fractions are $0.01\%$ $0.07\%$, respectively. particles, which initially randomly positioned, ultimately display characteristic spatial distributions can be categorised into four modes. Modes $(i)$ to $(iii)$ observed Taylor vortex regime, while mode ($iv$) encompasses both wavy vortex, turbulent regimes. Mode corresponds stable orbits away from cores. Remarkably, narrow $\textit{Ta}$ range, particles get trapped cores (mode ($ii$)). is transition when modes $(ii)$ observed. For $(iv)$, distribute throughout domain due instabilities. All show orientational statistics. find clustering for ($ii$) size-dependent, with main observations. Firstly, agglomeration at core much higher $\ell/d=0.2$ compared $\ell/d=0.1$. Secondly, range depends size. this we observe align strongly local cylinder tangent. most pronounced alignment around $\textit{Ta}=4.2\times10^5$. This observation found closely correspond minimum axial vorticity ($\textit{Ta}=6\times10^5$) explain why.