LAUSR

A fully resolved simulation is performed on the motion of spherical bubbles in homogeneous turbulence subject to a vertical flow that is uniformly sheared in a horizontal direction in order to understand the effect of turbulence on the transverse migration of rising bubbles. It is assumed that bubbles are fully-contaminated by surfactants and can be regarded as light solid particles. An immersed boundary method is adopted to represent a spherical bubble. We focus on the bubbles whose Stokes number based on the Kolmogorov scale is nearly unity. The Galileo number is set in the range of 35?50, for which positive lift is expected in laminar shear flow. Numerical results show that the direction of the mean transverse migration is reversed in turbulence, as in the case of small clean bubbles (Tanaka 2013 J. Phys. Soc. Japan 82, 044401). It is also found that the motion of the bubbles accumulated in the low-speed regions beside vortex layers mainly contributes to the reversal of the direction of the bubble transverse migration.