EXPERIMENTAL INVESTIGATION OF SKINFRICTION IN MULTY LAYER FLOW

Drag and friction forces in all external and internal flows, are the major factors of design parameters. Drag reduction may result in great energy saving of all kinds of vehicles and fluid transpotation.Exact physical realization of fluid friction forces, especially the turbulent boundary layer, and methods of friction reduction, still needs much further theoretical and experimental investigations.Tn this investigation, we experimented in pipes and channel with multi layered flows ,containing hydrogen bubbles or fine particles. We also studied the secondary layer of low viscousity fluid at the solid boundary and its effects on the skin friction.Review of previous theoretical and experimental studies, and our experimental results show that; introduction of the intermediate layer of fluid and particles effected the turbulence structures of boundary layer, the wall velocity gradient, relative roughness, and in turn considerable percentage decrease of friction and drag force.In this paper some recent works related to shear stress, skin friction and fluids containing particles have been analysed, and in parallel to theoretical investigation, four sets of experiments: (a) Hydrogen bubble at the channel bed, (b) turbid-density current, (c)and (d)suspended particles flow in smooth and rough pipes, and (e) two layered flow are reported.