Laser-Doppler anemometer measurements of turbulent structure in non-Newtonian fluids

Abstract

A laser-Doppler anemometer was used to measure the radial variation of axial turbulent velocity in the flow of water and aqueous polymer solution through a round pipe. Results were obtained for the mean velocity the turbulent intensity, and the one-dimensional energy spectrum. The polymers used were polyacrylamide (Separan AP 273; in a concentration range 25-200 WPPM). Both polymers are well known as effective additives to reduce turbulent drag, when dissolved in water to give a solution concentration of a few PPM. The mean velocity and turbulent intensity were both found to be increased by the polymer additives, with the magnitude of the effect depending on the polymer concentration This was in agreement with the results of other investigations. At low additive concentrations, the energy spectra were found to be identical to those for water flows; this also was in agreement with previous results. At higher concentrations, energy spectra showed noticeable attenuation in the largest (dissipation) range of wavenumbers. There was a corresponding enhancement of the small-wavenumber (energy-containing) range. This seemed to be a threshold effect with onset at a concentration of between 50 PPM and 100 PPM for Polyox WSR 301 and between 25 PPM and 50 PPM for Separan AP 273.