Dynamics of spherical and oblate particles in a viscoelastic shear flow

This study employs a direct-forcing fictitious-domain method combined with the Oldroyd-B model to investigate the dynamics of spherical and oblate spheroidal particles in a viscoelastic shear flow. By varying the particle Reynolds number (0.1 ≤ Re _p ≤ 10) and the Weissenberg number (1 ≤ Wi ≤ 5), we systematically examine the changes in particle equilibrium positions and rotational behaviours. For spherical particles, the equilibrium position shifts monotonically towards the wall with increasing Wi when Re _p < 1 or Re _p > 3, whereas it remains largely insensitive to elasticity for 1 ≤ Re _p ≤ 3. For oblate particles, the rotational period increases steadily with Wi across low-to-moderate Re _p , demonstrating that enhanced fluid elasticity significantly reduces the rotational speed. Owing to the interplay of fluid inertia and elasticity, oblate particles initialised with two representative initial orientations, denoted as n _{p 1} and n _{p 2} (specified by Euler angles as n _{p 1} = (0, 0, 0) and n _{p 2} = ( π /2, π /4, π /2)) exhibit six distinct modes of lateral migration and rotational motion. Under weak fluid inertia, increasing elasticity induces a kayak-like rotation, while at moderate inertia, the motion is dominated by rolling within the shear plane. When Re _p ≥ 7, the rotation may become locked, and this locked state can be released as Wi increases.