Introduction - It is well known that the injection of dilute polymer solutions into the boundary layer on two-dimensional hydrofoils produces changes in both the drag and lift of the foils, with the changes being dependent on the polymer , 3 its concentration , the injection technique , the location of the injection slit , and the rate of injection [1, 4, 5]. Previous tests  have also shown that the observed drag reduction does not necessarily increase linearly with the rate of injection of the polymer. Indeed, beyond a certain injection rate, further increases lead to little or no drag reduction and, in some cases, actually lead to a drag increase. Thus, one question that is of considerable practical interest is the effect of multiple injections of a given amount of polymer from several chordwise locations as compared with that due to the injection from a single location. The present study investigates the effects on lift and drag of a 20.16-cm (8 in) chord NACA 684–010 two-dimensional hydrofoil due to multiple injections of 200-ppm Polyox WSR 301 solution from several chordwise locations. The results indicate that, for a given flux of polymer injection, multiple injections from properly selected locations as compared with the injection from a single location result in a larger drag reduction without adversely affecting the foil lift.
A Note on Lift and Drag Effects Due to Polymer Injections from Several Locations on a Symmetric Hydrofoil
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Sinnarwalla, A. M., and T. R. Sundaram. "A Note on Lift and Drag Effects Due to Polymer Injections from Several Locations on a Symmetric Hydrofoil." J Ship Res 22 (1978): 257–258. doi: https://doi.org/10.5957/jsr.19220.127.116.117
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