Fig. 9
Lift/drag of the internal propagating wave acting on the centerline particles. a shows a top view of the particle bed, where lift forces are measured at the red-colored centerline particles. b shows the lift force normalized by the gravitational force, F L /F G , versus time for the centerline particles, each particle represented by a separate curve. c shows the position of the internal wave front versus time, where the position is determined either from the concentration profile, the drag force acting on the particle bed, or the lift force acting on the particle bed