Patent Application
20250020108
Turbine blades are the primary elements of wind turbines for converting wind energy into electrical energy. Turbine blades typically consist of a suction side shell member and a pressure side shell member that are bonded together at bond lines along a leading edge and a trailing edge of the blade. The bond lines are generally formed by applying a suitable bonding paste or compound along the bond line at a minimum designed bond width between the shell members.
Defects occur in the turbine blades from the original manufacturing process or as a result of operational conditions experienced by the blade. For instance, fatigue crack defects in multi-layer composite structures (such as root bushings) within the turbine blade are very common and these defects cause the turbine blades to come loose off their root bushings and separate from the rotor hub. Structurally, metal bushings at the root of turbine blades, when worn out, may not be able to carry the loads of the rotating blade and become loose. The rotating blades typically slip down from the root bushings at the bottom on a down-swing and impact on the root bushings on a top-swing, causing alternating cycles of tensile and compressive forces on the root bushings. As a result, gaps may develop between the blade and the root bushings. The root bushings, firmly attached to the rotor hub, may finally yield and liberate the blade, resulting in catastrophic turbine failure.
Existing solutions in the wind industry include completely scrapping a faltering blade and procuring a new replacement blade. Otherwise, the damaged blade may have to be taken down, repair holes may have to be bored in the damaged bushings and the bushings may have to be treated with bonding adhesive before being reinstalled. In that event, the internal ridges inside the damaged bushings are commonly drilled out and the repair method relies completely on the strength of the newly introduced bonding adhesive.
Another common industry solution for subsurface defects in blade laminates calls for grinding of the effected blade area and subsequent reapplication of the laminate materials. A defect is removed by grinding/sanding the laminate plies until the defect is exposed. The laminate layers are then reapplied and sanded smooth. Typically, an “over-laminate” ply is added to the repair area for additional strength. However, this additional laminate layer extends above the planar surface of the surrounding blade area and thus disrupts airflow over the blade and degrades aerodynamic performance. In addition, the grind/over-laminate repair procedure requires extensive surface preparation and skills to apply the repair laminate materials, followed by sanding, over-laminating, and painting, all of which are quite laborious and time consuming.
Fatigue crack defects are prevalent in wind industry for many different blade designs and/or types and it has been a challenge to transfer load from metal to composite. The wind turbine blade manufacturing industry has not been able to satisfactorily address manufacturing defects and/or operational conditions defects. In effect, wind turbine blade design and development have primarily focused on wind turbine blades and not root bushings. As a result, performance has been affected and wind turbine blades have failed at the root bushings more often than they should probably have.
Further, blade defects are typically needed to be repaired on-site, to ensure efficient operation of the wind turbine over its design life and power rating.
Accordingly, the industry would benefit from an improved repair procedure for wind turbine blades that is less time consuming, particularly suited for on-site repairs, and results in consistent and structurally sound repairs.
The accompanying drawings, which are included to provide a further understanding of the disclosed subject matter, are incorporated in and constitute a part of this specification. The drawings also illustrate implementations of the disclosed subject matter and together with the detailed description explain the principles of implementations of the disclosed subject matter. No attempt is made to show structural details in more detail than can be necessary for a fundamental understanding of the disclosed subject matter and various ways in which it can be practiced.
Various aspects or features of this disclosure are described with reference to the drawings, wherein like reference numerals are used to refer to like elements throughout. In this specification, numerous details are set forth in order to provide a thorough understanding of this disclosure. It should be understood, however, that certain aspects of disclosure can be practiced without these specific details, or with other methods, components, materials, or the like. In other instances, well-known structures and devices are shown in block diagram form to facilitate describing the subject disclosure.
Various implementations of the disclosed subject matter relate generally to and may provide improvements to apparatus, systems, and methods to the field of wind turbines, and to a method, system, and a kit for repairing damaged root bushings wind turbine blades. More particularly, the disclosed subject matter relates to a process for repairing fatigue cracks in composite laminate structures by utilizing an injection method that injects a structural adhesive into cracks and porous composite laminates. As a non-limiting example, the adhesive may be a self-etching thermoplastic adhesive which helps in bonding with surfaces that are contaminated with leaks from hydraulic pitch system oils or grease. Further, the thermoplastic adhesive may be heated and re-heated and essentially “self-healed”. In other words, if a damage is found during a post-repair inspection, heat blankets may be applied and a defective repair may be repaired again without having to reinject new adhesive. The process additionally uses the same method to inject cleaning chemicals and surface preparation chemicals to prepare several composite bonding surfaces for adhesive injection application.
In an aspect of the disclosed subject matter, a method for repairing fatigue cracks in a multi-layer composite body is disclosed. The method includes repairing fatigue cracks at a first interface between a first layer and a second layer of the multi-layer composite body and repairing fatigue cracks at a second interface between the second layer and a third layer of the multi-layer composite body. The method may also include anchoring the second interface with the third layer of the multi-layer composite body to prevent failure from fatigue cracks.
The method repairing fatigue cracks at the first interface between a first layer of the multi-layer composite body and a second layer of the multi-layer composite body may include drilling a first series of flush holes and a first series of weep holes extending from an outer surface of the composite body to the first interface. The method may further include flushing the first series of flush holes and the first series of weep holes with a high-pressure flushing fluid and drying the first series of flush holes and the first series of weep holes with an air jet. The method may also include drilling a first series of fill holes extending from an outer surface of the composite body to the first interface and installing fluid injection ports in the first series of fill holes. The method further includes injecting a crack-repair fluid through the injection ports to fill the first series of fill holes and thermally curing the crack-repair fluid deposited in the first series of fill holes.
Fatigue cracks at a second interface between the second layer and a third layer of the multi-layer composite body may be repaired by drilling a second series of flush holes a second series of weep holes extending from the outer surface of the composite body to the second interface, flushing the second series of flush holes and the second series of weep holes with a high-pressure flushing fluid, and drying the second series of flush holes and the second series of weep holes with an air jet. Further, a second series of fill holes may be drilled from an outer surface of the composite body to the second interface and fluid injection ports may be installed in the second series of fill holes. The method may also include injecting a crack-repair fluid through the injection ports and filling the second series of fill holes and thermally curing the crack-repair fluid deposited in the second series of fill holes. The second series of fill holes may be arranged and spaced relative to the first series of fill holes in a predetermined force transfer pattern.
Anchoring the second interface against failure from composite fatigue crack may include inclining some of the second series of fill holes transverse to the first series of fill holes and extending the inclined at least one of the second series of fill holes from the third layer through the second layer to the first layer.
The method may also include repairing fatigue cracks at a third interface between the third layer of the multi-layer composite body and a fourth layer of the multi-layer composite body, and anchoring the third interface with the fourth layer of the multi-layer composite body to prevent failure from fatigue cracks.
Repairing fatigue cracks at the third interface between the third layer of the multi-layer composite body and the fourth layer of the multi-layer composite body may include drilling a third series of flush holes and a third series of weep holes extending from the outer surface of the composite body to the third interface, flushing the third series of flush holes and the third series of weep holes with a high-pressure flushing fluid, and drying the third series of flush holes and the third series of weep holes with an air jet. The method may further include drilling a third series of fill holes extending from an outer surface of the composite body to the third interface and installing fluid injection ports in the third series of fill holes. The method may also include injecting a crack-repair fluid through the injection ports and filling the third series of fill holes and thermally curing the crack-repair fluid deposited in the third series of fill holes. The third series of fill holes may be arranged and spaced relative to the second series of fill holes in a predetermined force transfer pattern.
Anchoring the third interface against failure from composite fatigue crack may include inclining some of the third series of fill holes transverse to the second series of fill holes and extending the inclined at least one of the third series of fill holes from the fourth layer through the third layer to the second layer.
In an aspect of the disclosed subject matter, a wind turbine blade with a repaired root bushing is disclosed. The wind turbine blade may include a blade body with a pressure side and a suction side joined at a leading edge and a trailing edge. The blade body may longitudinally extend from a root region to a tip region through a transition region that extends between the root region and the tip region. The blade body may be mechanically connected with a rotor hub through a number of root bushings installed in the root region. The repaired root bushings may include a multi-layer composite body with fatigue cracks repaired at a first interface between a first layer of the multi-layer composite body and a second layer of the multi-layer composite body. There may be other fatigue cracks repaired at a second interface between the second layer of the multi-layer composite body and a third layer of the multi-layer composite body. The second interface is anchored with the third layer of the multi-layer composite body.
In operation, the fatigue cracks at the first interface between the first layer of the multi-layer composite body and the second layer of the multi-layer composite body may be repaired by drilling a series of flush holes from an outer surface of the composite body of the root bushing to the first interface. The flush holes may be initially flushed with a high-pressure flushing fluid and subsequently dried with an air jet. Further, a series of weep holes may be drilled from an outer surface of the composite body to the first interface. Like the flush holes, the weep holes may be flushed with a high-pressure flushing fluid and dried with an air jet. In addition, a series of fill holes may be drilled from an outer surface of the composite body to the first interface and fluid injection ports may be installed in the fill holes. A crack-repair adhesive fluid may be injected through the injection ports and deposited in the first series of fill holes. The crack-repair adhesive fluid may be thermally cured after being deposited in the first series of fill holes.
In a similar structure, the fatigue cracks at the second interface between the second layer of the multi-layer composite body and the third layer of the multi-layer composite body may be repaired by drilling a second series of flush holes from an outer surface of the composite body of the root bushing to the second interface. The second series of flush holes may be initially flushed with a high-pressure flushing fluid and subsequently dried with an air jet. A second series of weep holes may be drilled from an outer surface of the composite body to the second interface. Like the second series flush holes, the second series weep holes may be flushed with a high-pressure flushing fluid and dried with an air jet. In addition, a second series of fill holes may be drilled from an outer surface of the composite body to the second interface and fluid injection ports may be installed in the fill holes. A crack-repair adhesive fluid may be injected through the injection ports and deposited in the second series of fill holes. The crack-repair adhesive fluid may be thermally cured after being deposited in the second series of fill holes.
The second series of fill holes may be arranged and spaced in a predetermined force transfer pattern relative to the first series of fill holes. Further, some of the second series of fill holes may be inclined transverse to the first series of fill holes and extended from the third layer through the second layer to the first layer, to anchor the second interface with the third layer of the multi-layer composite body.
The wind turbine blade may include more fatigue cracks repaired at a third interface between the third layer and a fourth layer of the multi-layer composite body. The third interface may be anchored with the fourth layer of the multi-layer composite body.
In a similar structure, the fatigue cracks repaired at the third interface between the third layer and the fourth layer of the multi-layer composite body may be repaired by drilling a third series of flush holes from an outer surface of the composite body of the root bushing to the third interface. The third series of flush holes may be initially flushed with a high-pressure flushing fluid and subsequently dried with an air jet. Further, a third series of weep holes may be drilled from an outer surface of the composite body to the third interface. Like the third series of flush holes, the third series of weep holes may be flushed with a high-pressure flushing fluid and dried with an air jet. In addition, a third series of fill holes may be drilled from an outer surface of the composite body to the third interface and fluid injection ports may be installed in the fill holes. A crack-repair fluid may be injected through the injection ports and deposited in the third series of fill holes. The crack-repair fluid may be thermally cured after being deposited in the third series of fill holes.
The third series of fill holes may be arranged and spaced in a predetermined force transfer pattern relative to the second series of fill holes. Further, some of the third series of fill holes may be inclined transverse to the second series of fill holes and extended from the fourth layer through the third layer to the second layer, to anchor the third interface with the fourth layer of the multi-layer composite body.
In an aspect of the disclosed subject matter, a repair kit for repairing a damaged root bushing in a wind turbine blade is disclosed. The repair kit may include a drill template configured and arranged to go around a multi-layer composite body. The drill template may define drill locations for a series of flush holes, weep holes, and fill holes in the multi-layer composite body. The repair kit may also include a quantity of crack-repair fluid suited for repairing cracks in the multi-layer composite body and an injector tool configured and arranged to inject the crack-repair fluid through the fill holes.
The wind turbine blade 116 typically includes a blade body 120 with a pressure side 122 and a suction side 124 joining at a leading edge 126, and a trailing edge 128. The blade body 120 longitudinally extends from a root region 132 to a tip region 134 through a transition region 136 extending between the root region 132 and the tip region 134. The blade body 120 is mechanically connected with the rotor hub 118 through a number of root bushings (described in more details in connection with
To elaborate further, an example Type A repair process 224 may be carried out at a first interface between a first layer (typically a metal bushing) and a second layer (typically a glass wrap) of the root bushing 140. Fatigue cracks may occur at several failure zones localized at the first interface. The fatigue cracks at the first interface between the first layer and the second layer of the root bushing 140 may be repaired by mapping and drilling a series of flush holes (also referred to as “Type A flush holes”) from an outer surface of the root bushing 140 to the first interface, as in 234. The series of flush holes may be initially flushed with a high-pressure flushing fluid and subsequently dried with an air jet, as in 236. A series of fill holes (also referred to as “Type A fill holes”) may be drilled from an outer surface of the root bushing 140 to the first interface, as in 236 and fluid injection ports may be installed in the fill holes, as in 242. A crack-repair adhesive fluid may be injected through the injection ports and deposited in the fill holes, as in 244. The crack-repair adhesive fluid may be thermally cured after being deposited in the fill holes, as in 246. In effect, the repair at the first interface transitions the failure zones from the first interface to the second interface.
Fatigue cracks may additionally occur at several other failure zones localized at the second interface between the second layer (glass wrap) and a third layer (typically pultrusion) of the root bushing 140. The fatigue cracks at the second interface may be repaired with the crack-repair adhesive fluid. The repair at the second interface reinforces and anchors the second interface with the third layer of the root bushing 140 to prevent failure from fatigue cracks.
Referring back to
Referring once again to
Example Type C repairs 294 may be the third and final repair carried out at the interface between pultrusions 292 and glass laminates 296. Type C repairs 294 may build on the Type A repairs 282 and Type B repairs 292 such that the third series of fill holes (
Further, there may be a second interface (288,
Referring back to
The example drilled holes 302, 304, 306, 312, 314, 316 and the like may be flushed with modified pressure washer and cleaning fluids until the exiting fluid appear clean. Optionally, compressed air may also be used to blow out any residual cleaning fluids from any cavity. The cleaning and flushing processes may typically begin at the tip side of the wind turbine blade and progress on to the root side of the wind turbine blade because usually there may be a solid laminate behind the tip side that blocks the exit of cleaning and flushing fluids.
As has been mentioned earlier, the root bushings may get coated with leaked hydraulic fluid and cleaning fluids such as mineral spirits may need to be applied to get rid of the leaked hydraulic fluid. In effect, the cleaning fluids may treat the surface of application and prepare a chemically active surface. Operationally, flush holes and weep holes may be drilled in the vicinity of the cracks and microcracks and after drilling, the flush holes and the weep holes may be flushed with cleaning fluids. The cleaning fluids may be usually volatile and not easily flammable. Any remaining residual cleaning fluid may evaporate out. In an embodiment, compressed air may be blown to facilitate evaporation of any residual cleaning fluid.
The flush holes and the weep holes are flushed with a high-pressure flushing fluid, typically with a pressure washer such that a correctly oriented tip is inserted into the flush holes and the weep holes. As the flushing process progresses, a contaminated dirty solution comes out of weep holes and the flushing is continued until the solution becomes cleaner. Subsequently, the flush holes and the weep holes are dried with a compressed air jet correctly oriented into the respective holes. Subsequently, the flush holes and the weep holes are allowed to settle over a period of time so that all cavities are completely dry of the flushing solution.
Optionally, vacuum pumps may be used on the root side to suck the flushing and cleaning fluid through. The vacuum created by the vacuum pumps may effectively boil off any residual cleaning remaining in the cavities and dry out the cavities. Vacuum, however, has a limiting pressure value of 14.7 psi, which is less that the Zerk fitting pressure of thousands of psi. Vacuum suction is likely to be most effective when complete sealing is possible. Further, if the repair is performed down-tower, then drill holes may be drilled in different directions along the bushing. There may be other alternative ways to create the flushing and cleaning pressure such as using gas under pressure. Further, a threaded nozzle may be used for flushing and cleaning after the flushing and cleaning after the rotor blade bolts are removed.
Referring back to
Sometimes, it may be advantageous to repair a blade at its load-neutral 3 o'clock or 9 o'clock positions that offer favorable load distribution. Usually, non-destructive testing and inspections methods may be carried out before and after the repairs to evaluate the extent and state of porosity and to assess how to tune the repair efforts for better effects.
In operation, a structural adhesive (also referred to as “adhesive”) may be injected into a fractured laminate to repair a wind turbine blade root bushing. As a non-limiting example, the adhesive used in various implementations of the disclosed subject matter may be MethylMethacrolate (MMA) 8120, commercially available off-the-shelf. This adhesive is self-etching, compatible with fatigue conditions and effective with both metals and composites. MMA 8120 possesses low viscosity and does not need to be thinned to reach the laminate cracks and microcracks, driven by pressure. In addition to MMA 8120 other polymers such as epoxy, polyester, vinyl ester, poly eurethane, general eurethane may be used to treat and repair composite fatigue cracks. Further, other polymeric compounds typically used in structural concrete repairs may be used to treat and repair composite fatigue cracks.
Structurally, it is more effective to distribute the weight load of a hanging blade, whether in a commonly known 6 o'clock or a 12 o'clock position, with the internal ridges in place, instead of relying completely on the shear strength of adhesives or resins. The operation is safe, simple and uncomplicated. A hole may be drilled into the damaged laminate and the adhesive may be injected into the hole. This way, the damaged laminates may be brought back to original, if not a better state, by reintroducing mechanical connections that might have worn out over time. This is accomplished by not relying solely on the shear strength of adhesives and resins and rather by reinforcing the shear strength by distributing the tensile and compressive loads over the ridges within the root bushings.
In case of Type B repair (explained in more details later), offset fill holes are drilled to repair the defects between the glass and the pultrusion and flushing may not be possible because the cracks and the microcracks may be too small for any cleaning fluid to access. Type C repair (explained in more details later) may be performed in case of a much smaller cavity and the same structural method may be used. The material, however, may need to be changed and resin may be used instead of adhesives.
The preconfigured dimensions of the drill template 320, such as a length of a first series of holes 322 on an example first root bushing, a length of a second series of holes 324 on the example first root bushing, a length of a first series of holes 326 on an example second root bushing, a length (i.e., the longer of two planar dimensions) of a second series of holes 328 on the example second root bushing, total length (i.e., the longer of two planar dimensions) of the template 332, total width (i.e., the shorter of two planar dimensions) of the template 334, the distance of the farthest hole from the base line 336, the distance of an example middle hole from the base line 338, the distance of the closest hole from the base line 342, the distance between two rows of holes corresponding to two different bushings 344, the distance between two rows of holes corresponding to one example bushing 346, the distance of the first rows of holes from the side line 348, the distance of the second row of holes from the side line 352 and the like may be optimized by trial and error and/or parametrized in terms of the original dimensions of the bushings. The drilling pattern, the distance between fill holes and the adhesive injecting mechanism impact the performance and effectiveness of the repair. In an example set-up, four holes are drilled 80 mm apart.
Referring back to
The fill holes 386 may be marked and drilled such that the fill holes 386 extend from the outer surface of the composite body to the third interface. Fluid injection ports may be installed in the third series of fill holes 386. A crack-repair fluid (structural adhesive) may be injected through the injection ports until the fill holes 386 are completely filled with the crack-repair fluid. The crack-repair fluid deposited in the third series of fill holes may be thermally cured over a predetermined period of time.
In effect, the repair at the third and final interface 294 may reinforce and anchor the third interface 294 with the fourth layer (glass laminate) 296 to prevent failure from fatigue cracks. Specifically, some of the third series of fill holes may be laid out in an inclined direction transverse to the third interface such that the inclined fill holes extend from the fourth layer to the third layer as anchor support. The drilled and filled hole 386, extending through the pultrusion into the metal bushing, may structurally perform as anchor rods that reinforce the third interface. The adhesive material is dispensed into a grease gun using a glue gun.
The second series of fill holes may be arranged and spaced in a predetermined force transfer pattern relative to the first series of fill holes to transition the first composite fatigue crack failure zones from the first interface to the second interface. Further, some of the second series of fill holes may be inclined transverse to the first series of fill holes and extended from the third layer through the second layer to the first layer, to anchor the second interface with the third layer of the multi-layer composite body.
The wind turbine blade may include more fatigue cracks repaired at a third interface between the third layer of the multi-layer composite body and a fourth layer of the multi-layer composite body. This repair transitions composite fatigue crack failure zones from the second interface to the third interface and the third interface is anchored with the fourth layer of the multi-layer composite body.
The third series of fill holes may be arranged and spaced in a predetermined force transfer pattern relative to the second series of fill holes to transition the second composite fatigue crack failure zones from the second interface to the third interface. Further, some of the third series of fill holes may be inclined transverse to the second series of fill holes and extended from the fourth layer through the third layer to the second layer, to anchor the third interface with the fourth layer of the multi-layer composite body.
The repair kit 502 may also include a quantity of crack-repair fluid 512 suited for repairing cracks in the multi-layer composite body and an injector tool 514 configured and arranged to inject the crack-repair fluid through the fill holes. The crack repair fluid 512 may be a self-etching adhesive that enables surface preparation of the composite while also providing a chemical bond that may be stronger than the original design. The injector tool 514 may be a drill designed to create injection bore holes conforming to specified dimensions without tearing the composite laminate and to ensure that the holes are installed at specified angles and pitches to the blade surface. The kit 502 may optionally include an instruction manual 516 describing operating instructions to an intended user of the kit 502.
The methods of repair described above, however, are not limited to wind turbine blade root bushings and may be applied to fatigue/laminate crack repair in any composite, in general. Operationally, the adhesive may be injected under pressure and/or in a predetermined volume to repair a cracked laminate and to bring the laminate back to nominal strength. The adhesive may be self-etching and acidic, such that it would burn the surface of application and enhance surface adhesion. First, a number of holes are prepared and surfactants are injected, as dispersant, into the holes to flush out any contamination remaining in any cavity. Further, the adhesive may be heated up for re-bonding. In an embodiment, resins may be used instead of the adhesive to reconnect laminate layers. A predetermined level of pressure may be exerted for the adhesive to find its way into the cracks and microcracks of the laminate and to heal the manufacturing defects.
In the above description, numerous specific details such as resource partitioning/sharing/duplication implementations, types and interrelationships of system components, and logic partitioning/integration choices are set forth in order to provide a more thorough understanding. Embodiments disclosed herein may be practiced without such specific details, however. In other instances, control structures, logic implementations, opcodes, means to specify operands, and full software instruction sequences have not been shown in detail since those of ordinary skill in the art, with the included descriptions, will be able to implement what is described without undue experimentation.
References in the specification to “one implementation,” “an implementation,” “an example implementation,” etc., indicate that the implementation described may include a particular feature, structure, or characteristic, but every implementation may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same implementation. Further, when a particular feature, structure, and/or characteristic is described in connection with an implementation, one skilled in the art would know to affect such feature, structure, and/or characteristic in connection with other implementations whether or not explicitly described.
For example, the figure(s) illustrating flow diagrams sometimes refer to the figure(s) illustrating block diagrams, and vice versa. Whether or not explicitly described, the alternative implementations discussed with reference to the figure(s) illustrating block diagrams also apply to the implementations discussed with reference to the figure(s) illustrating flow diagrams, and vice versa. At the same time, the scope of this description includes implementations, other than those discussed with reference to the block diagrams, for performing the flow diagrams, and vice versa.
The detailed description and claims may use the term “coupled,” along with its derivatives. “Coupled” is used to indicate that two or more elements, which may or may not be in direct physical or electrical contact with each other, co-operate or interact with each other.
While the flow diagrams in the figures show a particular order of operations performed by certain implementations, such order is illustrative and not limiting (e.g., alternative implementations may perform the operations in a different order, combine certain operations, perform certain operations in parallel, overlap performance of certain operations such that they are partially in parallel, etc.).
While the above description includes several example implementations, the invention is not limited to the implementations described and can be practiced with modification and alteration within the spirit and scope of the appended claims. The description is thus illustrative instead of limiting.
| Number | Date | Country | |
|---|---|---|---|
| 63526874 | Jul 2023 | US |
