Structure and method for a flexible trailing edge projection of an airfoil
A structure is proposed for traversing a fluid environment and reducing the interference of the fluid flow vector at a trailing edge of the structure. The structure comprises an elongate body having a root, a wingtip, a leading edge and the trailing edge. The structure has a plurality of flexible projections positioned along the trailing edge extending from a base to a tip. The plurality of flexible projections bend to conform to a curvature of the fluid flow vector at the trailing edge and have a first resonant frequency above an oscillating force generated by the fluid flow vector.
1 . A structure adapted to traverse a fluid environment, the structure comprising:
an elongate body having a length defined by a root to a wingtip, and a width defined by a leading edge to a trailing edge, the elongate body traversing a fluid;
a plurality of flexible projections coupled to a respective position along the trailing edge and extending from a base to a tip, the base and tip defining a length of a flexible projection within the plurality of flexible projections;
a pressure side extending along a chord length of the elongate body from the leading edge to the trailing edge;
a suction side extending along the chord length of the elongate body from the leading edge to the trailing edge and opposing the pressure side, the pressure side and suction side have a camber to cause the fluid traversing the elongate body to generate a local median fluid pressure vector at the trailing edge;
wherein the plurality of flexible projections bend to form a curvature extending from the base to the tip which conforms to the local median fluid pressure vector at the trailing edge of the elongate body, and the plurality of flexible projections have a first resonant frequency above an oscillating force generated by the local median fluid pressure vector; and
wherein the following condition is true for the plurality of flexible projections:
k p /L p 4 >k b /L b 4
where k p is the stiffness of the flexible projection, L p is the length of the flexible projection, k b is a stiffness of the elongate body, and L b is the chord length of the elongate body, such that a lowest resonant frequency of the plurality of flexible projections is above a lowest resonant frequency of the elongate body.
2 . The structure of claim 1 , wherein a thickness and stiffness of the flexible projection proximal to the base is greater than the thickness and the stiffness proximal to the tip such that the flexible projection attenuates vibrations generated by turbulence within the local median fluid pressure vector.
3 . The structure of claim 2 , wherein the length of the plurality of flexible projections are 18%-20% of the chord length.
4 . The structure of claim 1 , further comprising two or more sections of flexible projections each extending along a portion of the length of the trailing edge, the flexible projections within each section of the two or more sections having at least one of a different length or geometry than the flexible projections within adjacent sections.
5 . The structure of claim 1 , wherein each of the flexible projections has an increased length relative to an adjacent flexible projection positioned closer to the wingtip of the elongate body.
6 . The structure of claim 1 , wherein the bending of the plurality of flexible projections is controlled by structural properties of the flexible projection including at least one of stiffness value, a material composition, the length and a geometry of the flexible projection.
7 . The structure of claim 6 , further comprising two or more sections of flexible projections each extending along a portion of the length of the trailing edge, the flexible projections within each section of the two or more sections having different structural properties.
8 . The structure of claim 6 , wherein each of the flexible projections has a higher stiffness value than an adjacent flexible projection positioned closer to the wingtip of the elongate body.
9 . The structure of claim 6 , wherein the flexible projection is composed of at least two material sections each extending along a portion of the length of the flexible projection, each material section containing a different material composition than an adjacent material section.
10 . The structure of claim 1 , wherein the length of the plurality of flexible projections are 5%-30% of the chord length.
11 . The structure of claim 10 , wherein the coupling of the base to the pressure or suction side occurs through at least a mechanical fastener, an adhesive, chemical bonding or a weld.
12 . The structure of claim 1 , wherein the base of the flexible projection is integrated into the elongate body between the pressure and suction side of the trailing edge, and the base is securely coupled through at least one of an adhesive, a mechanical fasteners, a chemical bond, a tolerance fitting or a weld.
13 . The structure of claim 1 , wherein the flexible projection has a shore D hardness rating between 10-70 and a flexural strength between 100-500 MPa.
14 . The structure of claim 1 , wherein the flexible projection extends past the trailing edge at an angle of (+/−) 10 degrees relative to the centerline of the base.
15 . The structure of claim 1 , wherein the plurality of flexible projections are manufactured through at least one of casting, 3D printing, laser or water jet cutting, or injection moulding.
16 . The structure of claim 1 , wherein the elongate structure is part of an airfoil mounted to at least a wind turbine, a tidal turbine, an aircraft wing, a drone rotor or a seacraft.
17 . The structure of claim 1 , wherein the pressure gradient generated by the local median fluid pressure vector is between 1 MPa and 20 MPa.
18 . The structure of claim 1 , wherein the plurality of flexible projections have a geometry of a saw tooth, protruding rectangle, frills, double-edged serration, comb/brush teeth, riblet, fluting or fimbriae.