On rotational dynamics of a finite-sized ellipsoidal particle in shear flows

Abstract

The rotational dynamics of finite-sized ellipsoidal particles with different aspect ratios around their fixed mass centers in shear flows have been investigated by direct numerical simulations. Particles are fully resolved by a revised immersed boundary projection method, and their rotational motion is governed by Euler’s equation which is calculated in the particle-fixed frame. The particle Reynolds number varies from 10 to 300 based on the longest axis of the particle. The steady states of the prolate and oblate spheroids in uniform flow, linear shear flow with the moving top wall and fixed bottom wall, and wall-bounded turbulence are analyzed. It is observed that the longest particle axes are perpendicular to or have a large angle with the local flow direction in the flow-gradient plane, which leads to a large drag force. A linear stability analysis on the rotational motion of a finite-sized particle in uniform flow is also carried out for supporting this finding. In the linear shear flow, the influence of fluid inertia and fluid shear on the inclined angle is examined in detail. In wall-bounded turbulence, it is found that the particles in the buffer region and the outside of the boundary layer behave similarly in the mean sense as in the linear shear flow and uniform flow, respectively. The present results with intermediate to large particle Reynolds numbers can be regarded as a starting point to understand the dynamics of heavy finite-sized particles in viscous flows.