Drag reduction in fibre suspension

Spectacular reductions in turbulent friction can be obtained by adding small amounts of either long-chain polymers 1,2 , or macroscopic fibres 3,4 to a fluid. The polymer effect has been the more studied of the two. But one of the continuing puzzles is that measurements of the turbulent energy spectrum show no evidence of a direct eddy–polymer interaction, despite the fact that the influence of the polymers on the turbulence is so profound. Although some increase in energy may be observed at small wavenumbers (attributable to a decrease in the dissipation rate), inertial and dissipation range spectra in polymer solutions are unchanged from the newtonian result. In contrast with this situation, we have recently found very marked changes in energy spectra measured in fibre suspensions.