Experimental determination of circulation velocities inside drops

Velocities inside large drops suspended in a fluid flowing upward in a tapered glass tube were measured by darkfield particle trace photography. Drop Reynolds numbers were between 3.76 and 19. There was a slow decay of internal velocity and a change in circulatory pattern with the accumulation of minute amounts of colloidal impurities at the interface. The evidence indicates that streamlines leave the interface over the entire rear hemisphere of the drop as circulation is damped.