The feedback effect caused by bed load on a turbulent liquid flow
  Experiments on the effects due solely to a mobile granular layer on a liquid flow are presented (feedback effect). Nonintrusive measurements were performed in a closed conduit channel of rectangular cross section where grains were transported as bed load by a turbulent water flow. The water velocity profiles were measured over fixed and mobile granular beds of same granulometry by Particle Image Velocimetry. The spatial resolution of the measurements allowed the experimental quantification of the feedback effect. The present findings are of importance for predicting the bed-load transport rate and the pressure drop in activities related to the conveyance of grains. 
Erick de Moraes Franklin, Fab\'iola Tocchini de Figueiredo, Eug\^enio   Span\'o Rosa
physics.flu-dyn