Effect of polymer additives on the small-scale structure of grid-generated turbulence

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Abstract
The effect of polyethyleneoxide (Polyox grade WSR 301) on grid‐generated turbulence was investigated using laser anemometry and flow‐visualization techniques. It was found that the polymer additive reduced both the turbulent intensity and the rate of decay behind the grid. At typical drag‐reducing concentrations, turbulent energy spectra were qualitatively the same as those in water, in agreement with the results of other investigations. However, at higher additive concentrations, the dissipation‐range spectra showed noticeable attenuation. This seemed to be a threshold effect with onset at a polymer concentration between 100 and 250 ppm. This result was supported by photographs of dye‐injection tracer but in this case the onset concentration for small‐eddy suppression was between 50 and 100 ppm.