A novel method to design and fabricate an inflatable wind turbine blade

Abstract

As the demand for increased energy harvesting grows, wind turbine rotor diameters and blade lengths have been expanding. This, however, comes with rising manufacturing and transportation costs. Additionally, the non-recyclable nature of carbon fiber presents an environmental challenge. Consequently, there is a pressing need for innovative approaches in the design of large-scale wind turbine blades. The objective of this invention is to present a novel methodology for the design and fabrication of inflatable horizontal axis wind turbine blades. This approach incorporates critical geometrical and structural features, such as varying twist angles, trailing edges, and load-bearing structural components. The invention also outlines a robust, tested manufacturing process utilizing PVC-coated fabrics, resulting in blades that are significantly lighter and more energy-efficient. This proposed methodology is applicable to any wind turbine airfoil. For illustrative purposes, the NREL S822 airfoil is used as an example in the design and manufacturing of the inflatable blades

Description

A novel method to design and fabricate an inflatable wind turbine blade

[0001] As the demand for increased energy harvesting grows, wind turbine rotor diameters and blade lengths have been expanding. This, however, comes with rising manufacturing and transportation costs. Additionally, the non-recyclable nature of carbon fiber presents an environmental challenge. Consequently, there is a pressing need for innovative approaches in the design of large-scale wind turbine blades.

[0002] The objective of this invention is to present a novel methodology for the design and fabrication of inflatable horizontal axis wind turbine blades. This approach incorporates critical geometrical and structural features, such as varying twist angles, trailing edges, and load-bearing structural components. The invention also outlines a robust, tested manufacturing process utilizing PVC-coated fabrics, resulting in blades that are significantly lighter and more energy-efficient.

[0003] This proposed methodology is applicable to any wind turbine airfoil. For illustrative purposes, the NREL S822 airfoil is used as an example in the design and manufacturing of the inflatable blades.

[0004] This invention relates to the field of renewable energy, specifically to wind turbines and their components. More particularly, it addresses the design and manufacturing of wind turbine blades, with a focus on improving their aerodynamic efficiency, structural integrity, and sustainability. The invention also pertains to innovative materials and manufacturing techniques that aim to enhance the performance of wind turbine blades while reducing their environmental impact, particularly in terms of recyclability and cost-efficiency. Additionally, the invention seeks to address challenges related to the transportation and installation of large turbine blades, Keywords: Energy engineering – Mechanical design – Manufacturing – Wind energy – Renewable energy.

[0005] The present invention focuses on wind turbines that convert wind energy into electrical energy. A horizontal-axis wind turbine primarily consists of a rotor with three blades. These blades move when air flows around them, creating a pressure difference due to their aerodynamic shape (airfoil), which rotates the rotor. This rotation is then transmitted to the power generator. The longer the turbine blades, the greater the turbine's ability to generate electricity. For instance, the length of one blade reached 131 meters in 2024. As a result, manufacturing and transportation costs have increased, along with the difficulty of recycling the blades.

[0006] This invention uses the technique of compartmentalized structures to form the complex aerodynamic geometry of the blade while meeting the structural rigidity requirements necessary to withstand various blade loading conditions. The blade is constructed from three sections of unequal lengths, each with an inflated, bumpy shape. Each section has a twist angle that corresponds to the general twist of the entire blade. Inside these sections are several inflated, broken tubes with higher pressure, which function to increase the overall strength of the blade and reduce the likelihood of complete deflation. The final layer of the blade is made from a thin, elastic material that conforms to the crests of the bumpy-shaped sections.

[0007] 1. The size of wind turbines is continuously increasing, making it more difficult to manufacture and transport the blades, in addition to raising manufacturing costs. This has led manufacturers to seek more sustainable, though hard-to-recycle, materials. 2. Wind turbine blade graveyards have become an environmental disaster, as separating the materials used to manufacture turbine blades, such as fiberglass, carbon fibers, and bonding resins, is challenging, making recycling difficult. 3. Wind turbines also negatively impact migratory bird paths and stopover sites, as it is impossible to periodically collapse the blades due to their length and weight.

[0008] An innovative design and fabrication method for horizontal-axis wind turbine blades that makes them easier to manufacture, transport, install, maintain, and recycle, while also reducing their weight compared to commercially used blades.

[0009] The present invention provides a design for the inflated blade and a detailed method for manufacturing of each part separately, as there is no previous invention that has dealt with variable twist angles or even its stiffness and its ability to withstand wind loads, which makes it feasible to be implemented commercially.

[0010] The drawings illustrate the design of the inflated blade, its manufacturing method using specific materials, and the assembly process with the turbine rotor, aimed at producing a lighter inflatable wind turbine compared to those commercially available.

[0011] An inflatable twisted wind turbine blade

[0012] An inflatable blade cross section with load carrying beams

[0013] An isometric view for the three inflated partitions of the blade

[0014] The three partitions of the inflated blade with unequal lengths

[0015] The four sections of the inflated partitions

[0016] The welding method for the internal stiffener into the walls of the inflated partitions

[0017] The root partition of the blade connected to the rigid fixture

[0018] The rigid fixture of the blade with tilting angles for each tube

[0019] The intermediate angle between the tube segments

[0020] The closing adapter for the internal tubes

[0021] Forces and reactions acting on the inner tubes after pressurization

[0022] The fabrication method of the Internal straight tubes (rigidity members)

[0023] The effect of the inner pressure on the walls of the inner cylinders with (down) and without bow warping strip (up)

[0024] The difference between straight lofted tubes and curved lofted tubes

[0025] The fabrication method of the Internal curved tubes (rigidity members)

[0026] Type A tube terminal

[0027] Type B tube terminal

[0028] Type C tube terminal

[0029] The pear-shaped inflated design of the trailing edge

[0030] An isometric view for the pear-shaped trailing edge

[0031] The Morphing technique of the inflated trailing edge

[0032] The twisted loft between the upper and the lower sections of the trailing edge

[0033] The waving directions of the PVC coated fabrics

[0034] The pneumatic circuit for the inflatable blade

[0035] The basic structure of the invention is shown in. The inflatable blade1is constructed from three main partitions2, each has a specific length, so that the total length of the blade is 3L, and the lengths of those partitions are (0.5L, 1L, 1.5L),with criteria of dividing related to the twist angles, as each partition has its own twist angle (θ1, θ2, θ3). Each partition consists of upper and lower geometries where those geometries are to be inscribed in the airfoil shapeand a twisted loft is connecting between them to form the internal structure of the blade. The internal bumpy shaped inflated partitions are to be fabricated from PVC coated fabrics that doesn’t allow air leakage and generate high structural stiffness after being inflated.

[0036] Internal stiffeners7are welded internally to the inflated partitions2to maintain the contact lines between the inflated inner support body and the silicone layer5at the desired coordinates, where the connection between2and7is described inby following steps fromatodrespectively. This type of connection is necessary to prevent the geometry from collapsing, also an additional strip8is added to avoid air leakage. The shape of these connections is designed so that the forces acting on the weld are maintained in the shear direction and not in the tensile direction (T-peel tension direction).

[0037] After assembling the three partitions together (those inflated partitions2are forming the internal shape of the blade, in other words, they act as muscles in the human body), an outer skin is needed where this skin is made from elastic silicon covering5welded to be tangent to the inflated shape crests after being inflated with a pressure equals to 2bar at the lines indicated in. The use of the silicone cover instead of the PVC-coated fabric serves two purposes: the first is to ensure that all the required points are tangent to the crests, allowing the lower and upper cambers on both sides of the airfoil to be formed, in addition to achieving a smooth transition between the tangent lines to the bumpy inflated shape, and the other purpose is to make the blade withstand pitting and increase the puncture resistance of the composite wall against environmental challenges.

[0038] For the essential requirement of high blade stiffness to carry the working loads, even in flapwise or edge wise direction in addition to its own weight; a group of internal broken tubes3with inflation pressure up to 4 bar are designed and fabricated with initial tilting angles (α1, α2, …, α6) described inand with intermediate angles between tube segments. Those tubes are fabricated also from PVC coated fabrics and installed to be inscribed in the inflated body2.

[0039] Those Tubes are connected to the rigid fixtureusing Artelon turned part (closing adaptor)11, bended plate12and hose clamps19, with a construction described in. This construction allows for the connection to withstand radial forces and circumferential strain (D2-D1) in addition to forces due to internal pressure that will lead to the disassembly of the Artelon adaptor11.

[0040] This rigid fixture6has three main functions; to act as a rigid support between the inflatable blade and the rotor and to give the inner inflated tubes3their initial titling angles, also this fixture is used to avoid air leakage from the PVC jacketby using the sandwich idea of inscribing the PVC coated sheet between two layers one of them made from steel13and the other made from Artelon14, where the steel base profile13is designed with the bumpy shape final geometry after inflation and the Artelon base profile14is designed to take the root airfoil shape in order to assemble the silicon covering5tangent to this profile at the root of the blade.

[0041] The connection method of the rigid fixture to the rotor is by using a rotating shaft15fixed to the steel base profile13, this shaft is essential to provide the pitch control mechanism to adapt the angle of attack required. That shaft also contains the two hoses for pressurizing the inner tubes with 4 bar and the inflated partitions with 2 bar through pneumatic hoses and fittings16, 17, 18.

[0042] Because PVC fabrics are elongated when subjected to tensile stresses, additional weld strip10is required at the opposite direction of the main assembly strip9to avoid bow warping of the inner tubes. Another approach for the inner cylinders is to make its loft to be curved instead of being straight loftedthat is for the purpose of generating a smooth curved twist for the blade especially at the trailing edge. The way of fabrication and assembly for this curved cylinder is described in. At the free side of the tube the design of the terminal is described in, 17, and 18as it’s possible to use any of them to close the inner tubes.

[0043] To fabricate the sharp trailing edge: An asymmetric inner stiffener tube (pear shaped)4is fabricated and welded to a straight double sided PVC edge, 20. This construction allows the morphing of the trailing edge without losing the airfoil after inflation by controlling the lengths of the welded silicon covering5. Also, a twisted loft is used to connect between the upper and lower sections to generate the twist angle for each partition of the blade three partitions.

[0044] All the dimensions should be modified to compensate for the strain that occurs when pressurizing the blade tubes and the blade body, after experimentally measure the elongation using standardsASTM D7510-6 or ISO 1421:2016.

[0045] The weaving direction of fabrics should be parallel to the blade longitudinal axis in order to keep the tension forces due to internal pressure at the weft or warp directions and not the bias direction.

[0046] Pressure regulators are used to keep the constant internal pressure values for the tubes and the outer.

[0047] The inflatable blades are specifically designed for use in the renewable energy sector, focusing on the development and manufacturing process of inflated horizontal axis wind turbine blades. This innovation aims to enhance the efficiency and durability of wind energy generation systems. These blades are intended for large-scale production and can be utilized in renewable energy applications, particularly in wind farms. The key benefits of this design include reduced weight, lower material costs, and simplified transportation and assembly. The technology described can be implemented on an industrial scale, as the design and fabrication process can be reproduced for blades of various sizes, following the steps outlined in this invention.

[0048] 1. Inflatable twisted wind turbine blade

[0049] 2. Inflated partitions

[0050] 3. Load carrying beams

[0051] 4. Pineapple-shape trailing edge

[0052] 5. Flexible silicon jacket

[0053] 6. Base and tubes fixation

[0054] 7. Internal Stiffeners

[0055] 8. Air leakage strip

[0056] 9. Assembly strip

[0057] 10. Bow warping strip

[0058] 11. Tubes closing adaptor

[0059] 12. Tilted welded plate

[0060] 13. Steel base profile

[0061] 14. Artelon base profile

[0062] 15. Connecting shaft

[0063] 16. Pressure inlet (4 bar)

[0064] 17. Pressure inlet (2 bar)

[0065] 18. Pneumatic fitting

[0066] 19. Hose clamp

[0067] No biological material has been deposited in connection with this invention.Patent Literature

[0068] Patent CN111692041

[0069] Publication Date: September 9, 2020

[0070] Title: “Flexible inflatable type wind turbine blade and manufacturing method thereof"

[0071] Applicant: Jiangnan University

[0072] Relevance: The invention discloses a flexible inflatable type wind turbine blade and a manufacturing method thereof

[0073] Patent US20100143130

[0074] Publication Date: June 10.2010

[0075] Title: “Inflatable wind turbine blade and method for forming said rotor blade"

[0076] Applicant: General Electric Company

[0077] Relevance: The invention discloses an inflatable rotor blade for a wind turbine includes a flexible skin.

Claims

An inflatable twisted wind turbine blade [1] constructed from three unequal lengths-inflated partitions (at 2 bar) from PVC coated fabrics [2] fig.3, 4. Those partitions are bumby-shaped and comprise a load carrying internal multi beams inflated at 4 bar [3] in addition to inflated welded pear-shape trailing edge (also inflated at 4 bar air pressure) [4], covered with flexible silicon jacket [5] and with rigid base and tubes fixation [6]. fig.1The design of the cross sections of the inflated beam fig.2 consists of: load carrying inflated cylinders [3], outer inflated jacket [2] with internal stiffeners [7], pear-shaped trailing edge [4], and outer silicon covering [5]. Note that the parts [2, 3, 4, and 7] are all made from PVC coated fabrics.The twist and lofted geometry of the partitions with the angles between upper and lower cross sections and the angles between the three partitions [θ1, θ2, θ3] fig.5The welding method required for the assembly of the internal stiffeners [7] to the bumpy- shaped inflated body [2], which is arranged in steps described in fig.7, where a welding strip [8] is added to avoid air leakage.The fabrication method of the Internal straight tubes (rigidity members) [3] fig.12, and the Internal curved tubes fig.15 with double welded stripes for assembly [9] and for warping prevention [10] which is caused due to unequal elongation of the material after pressurization fig.

13. with intermediate broken angles fig.9 and with terminals described in fig.16, 17, and 18The rigid closing adapter for each cylinder which consists of turned Artelon part [11], tilted welded plate with initial tilting angle [12], two hose clamps [18] to avoid air leakage and 4 bar air inlet [16] fig.10,11The Rigid connection between the tubes and the fixation base [12] that provides the tubes with initial tilting angles [α1, α2…α6] fig.8The connection for both the tubes adaptor, and the bumpy-shaped root of the blade fig.8, 10The fixation base design which connects the blade to the rotor fig.8, 10The three types of inflated cylinders terminals fig.16, 17, 18The pear-shaped inflated design of the trailing edge [4] fig 19, 20The Morphing Technique for the pineapple shape trailing edge [4] fig.21, and the geometry lofting all over the length of the trailing edge fig.22

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