Lift, drag, and pressure distribution effects accompanying drag-reducing polymer injection on two-dimensional hydrofoil

Lift and drag forces and pressure distribution were measured for a 10 cm. chord, 20 percent relative thickness, NACA 63 sub 4-020, symmetrical, two-dimensional hydrofoil, with and without drag-reducing polymer injection. The 200 ppm solution of Polyox WSR 301 was introduced into the foil boundary layer with an injection velocity of 10 percent of the free stream velocity. The injection slits were situated at 10 and 30 percent of the chord length. The pressure distribution data does not indicate any significant change of the separation point. It demonstrates, however, that the polymer injection always results in a significant decrease of pressure in the region aft of the injection slit. This decrease of the local pressure gives rise to a lift increase for injections made on the suction side of the foil surface and a lift decrease for injections made on the pressure side. The data suggest an elongational viscoelastic effect and a tentative explanation is offered.