Drag force on interacting spherical bubbles rising in-line at large Reynolds number

► The hydrodynamic interaction of two bubbles rising in vertical line is analyzed. ► The leading bubble shielding effect decreases the drag on the trailing bubble. ► A proper velocity for the trailing bubble drag is obtained from physical grounds on boundary layer theory for a single bubble. ► An explicit semi-analytic expression for the drag force on the trailing bubble is presented.