Turbulence Measurements in Pipe Flow With Drag Reducing Polymer Additives

Pressure drop and instantaneous velocity fields were measured for fully developed turbulent pipe flow of water and a solution of water and long chain polymer at low concentration. Two-dimensional Particle Image Velocimetry technique — PIV, coupled with a particle tracking technique was employed to yield velocity fields with high spatial resolution. Turbulence statistics were obtained from a series of approximately 2500 instantaneous velocity fields measured for each flow configuration characterized by the turbulent Reynolds number and the polymer concentration. Tests were conducted for a turbulent Reynolds number range from Reτ≈1764 to Reτ≈3154, and for 20 wppm of Superfloc A110 polymer in water. Time-averaged, rms velocity fluctuations and turbulent shear stresses profiles were measured. Drag reductions of the order of 50% were measured. Changes in the axial and wall-normal velocity fluctuations were measured and linked to the presence of the polymer. Reynolds stresses were also shown to decrease in the buffer layer of polymer solution flows as a result of a decrease in the correlation of axial and wall normal fluctuations. A deficit of the viscous shear stress and Reynolds stresses in relation to the total stress was measured close to the wall and attributed to the polymer stresses exerted on the fluid. All the results obtained were in agreement with the available literature, which serve to validate the procedures and test section employed in the experiments.