Local drag reduction due to injection of polymer solutions into turbulent flow in a pipe. Part II: Laser‐doppler measurements of turbulent structure

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Abstract
Aqueous solutions of polythyleneoxide (Polyox WSR‐301) were injected into a pipe flow through either a small tube at the center line or an annular slot in the wall. The solution contained polymer at an injection concentration of 1,000 wppm. Injection into water flow with a Reynolds number Re = 3.5 × 104 was at a rate which gave a mean polymer concentration of 5.0 wppm in the water flow. A laser‐Doppler anemometer (LDA) was used to measure the streamwise turbulent velocity at various radial positions and at several stations downstream from the injection point.Results were obtained for mean velocity and intensity profiles; autocorrelations; and one‐dimensional energy spectra. The mean bursting period was determined using the “short‐sampling‐time” autocorrelation method. Changes in all these quantities due to polymer injection were found to depend on the amount of local drag reduction at that particular downstream station but were independent of the local polymer concentration at the measuring point.