| 摘要 |
Methods are disclosed for increasing lift and decreasing drag on hydrofoils and swim fins. These methods include providing a hydrofoil with a highly swept back leading edge portion and orienting the hydrofoil at a significantly reduced angle of attack in which the reduced angle of attack occurs at an angle that is substantially transverse to the hydrofoil's direction of movement through a surrounding fluid medium. The lee surfaces of the hydrofoil is provided with a substantially unobstructed flow path as well as a separation reducing contour so as to permit lift generating attached flow conditions to form along such lee surfaces. Substantially rigid structural reinforcement is provided to prevent the hydrofoil from deforming significantly during use. Methods are disclosed for providing a hydrofoil with a substantially longitudinal recess or venting system located substantially along the center axis of the hydrofoil. The attacking surfaces of such a hydrofoil is provided with an anhedral contour that forms a substantially lengthwise channel with the recess or venting means located along the center axis of this lengthwise channel. The anhedral contour directs water toward the center axis of the lengthwise channel, and the central recess or venting system permits water to flow through it toward the lee surfaces in order to reduce the occurrence of outward directed spanwise flow conditions along the attacking surfaces and encourage inward directed spanwise flow conditions to occur along the attacking surfaces. The central recess or venting system also permits the water flowing in an attached manner along the lee surfaces of the hydrofoil to merge with the water flowing from the attacking surfaces through the recess or venting system so that lift is efficiently generated. Methods are disclosed for applying these lift generating and drag reducing methods to both non-flexible and flexible hydrofoil blades that are used in reciprocating propulsion strokes through a fluid medium. Methods are disclosed for permitting flexible hydrofoils to deform in a manner which permits such efficient flow conditions to form under significantly light reciprocating strokes while simultaneously providing sufficient structural reinforcement to enable such flow conditions to be maintained without experiencing undesirable forms of deformation. Also provided are methods for significantly controlling and reducing the build up of torsional stress forces within a flexible hydrofoil as it is encouraged to twist to a reduced angle of attack during use so that such a twisted form is created with significant improvements in efficiency, contour, and ease.
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