Drag Reduction in Hydraulics Flows

In hydraulic flows, the interactions between particles and turbulence can induce some drag reduction as observed with dilute polymer solutions, sediment laden flows and self-aerated flows. Data on drag reduction with suspended sediment flows, coal-water flows with dilute polymer and self-aerated flows are re-analysed. The mechanisms of drag reduction are explained and some analogies between these flows are developed. It is suggested that the presence of particles next to the bottom increases the effective viscosity of the mixture and the sublayer thickness. The results provide a better analysis of water-particle flows and a more accurate prediction of drag reduction.