In this work, turbulent drag reduction in a pipe is investigated by using laser Doppler velocimetry. The effect of decreasing the friction factor of the flow is obtained by addition of high molecular weight polymers. The mechanism of drag reduction is explained in terms of a stress anisotropy that inhibits the transversal transport of momentum by turbulent fluctuations. Semi-theoretical models based on a nonlinear constitutive equation, which takes into account an extra extensional rate of strain in the flow produced by the local additive orientation, are presented. The semi-theoretical models used to predict the friction factor of the flow in the presence of the polymer have successfully described the experimental measurements. The results have revealed a reduction in the friction factor of 65% for a concentration of 350 ppm in volume of polyacrylamide (PAMA) in an aqueous solution. In addition, the flow statistics, such as the axial and radial velocity fluctuations, the normalized autocorrelation functions as well as the power spectra for both velocity fluctuation components, are examined for the Newtonian flow of pure water and the flow of a 120 ppm solution of PAMA at the same friction velocity. Next, the results are compared in order to characterize the effect of the additive on the turbulent flow.

Experiments were carried out to study the effect of dilute aqueous polymer solutions on flow-generated cavitation inception. The cavitation inception on 1/4 and 1/2 -in-dia models with a hemispherical nose in a blowdown water tunnel was definitely inhibited at Reynolds numbers from 7 × 10 4 to 3.1 × 10 5 . Reduction of the incipient cavitation number to 30 percent of its value for tap water was observed, depending on the kind of polymer used, its concentration, and the Reynolds number. Flow velocity field visualization was achieved by optical techniques, which measured the flow velocities and was used to correct values computed from venturi pressure drop. For guar gum (300 ppm) tests, the computed velocities were approximately 8 percent low.