Hydrodynamic interactions suppress deformation of suspension drops in Poiseuille flow

摘要

Evolution of a suspension drop entrained by Poiseuille flow is studiednumerically at a low Reynolds number. A suspension drop is modelled by a cloudof many non-touching particles, initially randomly distributed inside aspherical volume of a viscous fluid which is identical to the host fluidoutside the drop. Evolution of particle positions and velocities is evaluatedby the accurate multipole method corrected for lubrication, implemented in the{\sc hydromultipole} numerical code. Deformation of the drop is shown to besmaller for a larger volume fraction. At high concentrations, hydrodynamicinteractions between close particles significantly decrease elongation of thesuspension drop along the flow in comparison to the corresponding elongation ofthe pure-fluid drop. Owing to hydrodynamic interactions, the particles inside adense-suspension drop tend to stay for a long time together in the central partof the drop; later on, small clusters occasionally separate out from the drop,and are stabilized by quasi-periodic orbits of the constituent non-touchingparticles. Both effects significantly reduces the drop spreading along theflow. At large volume fractions, suspension drops destabilize by fragmentation,and at low volume fractions, by dispersing into single particles.