On the Changes in Lift of Hydrofoils Due to Surface Injections of Polymer Additives
HYDRONAUTICS INC LAUREL MD
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Existing data on the effects on lift of symmetric hydrofoils due to the injection of polymer solutions on to their surfaces show that the lift can either decrease or increase depending on the polymer, injection velocity, location of injection, side of injection and angle of attack. A unified, albeit semiempirical, approach is suggested in the present report for correlating and explaining the apparently contradictory data. It is proposed that the observed lift changes may be due to the influence of the injections on the boundary-layer displacement effect that is known to reduce the circulation around hydrofoils. Four separate boundary-layer effects due to injection are identified and discussed, namely those due to changes in the effective angle of attack, the effective camber, the circulation in addition to the changes in circulation associated with the previous two effects, and the thickness distribution. Classical methods of airfoil theory are utilized to calculate the effective hydrofoil shape that would have produced the observed pressure distributions. This effective shape is utilized to identify the different boundary layer effects, and these, in turn, are identical with the changes likely to be produced by polymer injections.
- Marine Engineering
- Fluid Mechanics