On the structure of turbulent flow of drag reducing fluids

Abstract

Despite the fact that during the last two and half decades more than a thousand publications have appeared on the subject of turbulent drag reduction, this phenomenon is today still not well understood. A major reason is that it is necessary to consider not only the normal turbulence processes present in such flows but also the rheological properties of the respective fluids. To attain a better understanding it seems most helpful to analyse the modifications of the turbulence structure produced by drag reducing additives, typically a few tens of parts per million of an appropriate high molecular weight polymer, cf. the review article [1]. Statistical details of such flows can be obtained most accurately using laser-Doppler anemometry to measure average velocities, turbulence intensities and Reynolds stresses as well as space-time correlations and (equivalently) power spectra. Additionally flow visualization methods, such as dye injection, schlieren techniques and holographic interferometry are also helpful.