Lift and drag effects due to polymer injections on a symmetric hydrofoil

Experimental results are presented for the effects on the lift and drag of a two-dimensional hydrofoil due to the injection of dilute polymer solutions onto its surface. Results are presented for three different polymers, namely, Polyox, Polyacrylamide, and Jaguar; for the purposes of comparison, results are also presented for water injection. The results indicate that, in general, polymer injection leads to a reduction in drag; but the lift can either increase or decrease depending on the polymer, the angle of attack, the surface on which the injection is made, the chordwise location at which injection is made, and the injection velocity. Results for the effects of the injections on the pressure distributions on the hydrofoil are also presented, and these results are consistent with the force measurements. Examination of the pressure distribution data seems to suggest that the observed lift effects may be due to a boundary-layer displacement phenomenon, with the detailed nature of this displacement effect being dependent on the viscoelastic properties of the injected polymer.