Drag Reduction in Fibre- and Non-Fibrous Suspensions

Abstract

In the flow of paper pulp drag reduction was first observed six decades ago and in fine sand suspensions three decades ago. The drag reduction in fibre suspensions will be discussed with respect to fibre dimensions, fibre concentrations, fibre flexibility and fibre distribution in the flow. As for the other additives, their interaction with the structures of the turbulent flow, e.g., the drag reduction in fine sand suspensions, will be discussed in the frame of an inertial theory which shows that drag reduction can occur in a very limited range of concentration and size. This type of drag reduction also occurs in air flows.