U.S. patent application number 13/365029 was filed with the patent office on 2012-07-19 for highly reliabile, low cost wind turbine rotor blade.
Invention is credited to Frederick W. Piasecki.
Application Number | 20120180582 13/365029 |
Document ID | / |
Family ID | 44340944 |
Filed Date | 2012-07-19 |
United States Patent
Application |
20120180582 |
Kind Code |
A1 |
Piasecki; Frederick W. |
July 19, 2012 |
Highly Reliabile, Low Cost Wind Turbine Rotor Blade
Abstract
A wind turbine rotor blade and a wind turbine incorporating the
rotor blade include a first and second composite skin. A first and
a second spar pultrusion having a base and a plurality of integral
ribs generally normal to base are attached to the inside surface of
the first and second composite skins and extend the span of the
rotor blade. At least one shear web connects a rib of the first
spar pultrusion to a corresponding rib of the second spar
pultrusion. The width of the spar pultrusions decreases in a
step-wise fashion along the span of the rotor blade from the root
to the tip. The leading or trailing edge of the rotor blade may be
selectably opened for inspection and repair.
Inventors: |
Piasecki; Frederick W.;
(Haverford, PA) |
Family ID: |
44340944 |
Appl. No.: |
13/365029 |
Filed: |
February 2, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12757832 |
Apr 9, 2010 |
8192169 |
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13365029 |
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Current U.S.
Class: |
73/865.8 |
Current CPC
Class: |
Y02E 10/725 20130101;
Y02E 10/72 20130101; Y10T 29/49339 20150115; F03D 13/20 20160501;
F03D 1/06 20130101; Y02E 10/721 20130101; Y02E 10/728 20130101;
Y10T 29/49337 20150115; F03D 9/25 20160501; F03D 9/00 20130101;
B23P 15/04 20130101; Y10T 29/49336 20150115 |
Class at
Publication: |
73/865.8 |
International
Class: |
G01N 33/00 20060101
G01N033/00 |
Claims
1. A method of inspecting a rotor blade for a wind turbine, the
method comprising: a. providing a first skin and a second skin,
said first skin and said second skin each defining a trailing edge
portion, said trailing edge portion of said first skin being
releasably attached to said trailing edge portion of said second
skin; b. detaching said trailing edge portion of said first skin
from said trailing edge portion of said second skin; c. inspecting
the rotor blade.
2. The method of claim 1 wherein the rotor blade has a trailing
edge, said trailing edge being defined by said trailing edge
portions of said first and said second skins when said trailing
edge portions are releasably attached, said step of inspecting the
rotor blade further comprising: opening said trailing edge.
3. The method of claim 2 wherein said step of providing said first
skin and said second skin further comprising: providing a
mechanical lock, said mechanical lock releasably attaching said
trailing edge portions of said first and second skins one to the
other, said mechanical lock being located proximal to said trailing
edge.
4. The method of claim 3 wherein said step of providing said
mechanical lock further comprising: providing a male portion and a
female portion defining said mechanical lock, said male portion
being attached to said trailing edge portion of a one of said first
and second skins, said female portion being attached to said
trailing edge portion of the other of said first and said second
skins, said male and said female portions of said mechanical lock
releasably attaching said trailing edge portions of said first and
second skins one to the other.
5. The method of claim 4 wherein said step of detaching said
trailing edge portion of said first skin from said trailing edge
portion of said second skin comprising: detaching said male portion
and said female portion of said mechanical lock.
6. The method of claim 1 wherein said step of providing said first
and said second skins further comprising: providing a first spar
and a second spar, said first spar having an attachment to said
first skin, said second spar having an attachment to said second
skin, said first spar having an attachment to said second spar.
7. The method of claim 6 wherein said step of inspecting the rotor
blade further comprising: inspecting said attachment between said
first skin and said first spar, inspecting said attachment between
said second skin and said second spar, and inspecting said
attachment between said first spar and said second spar.
8. The method of claim 1 wherein the rotor blade has a leading edge
and each of said first and second skins defines a leading edge
portion, the method further comprising: providing a leading edge
skin, said leading edge skin being in a hinged connection to said
leading edge portion of a one of said first skin and said second
skin, said leading edge skin defining said leading edge of the
rotor blade.
9. The method of claim 8 wherein said step of providing said
leading edge skin further comprising: providing a leading edge skin
hinge, said leading edge skin hinge releasably attaching said
leading edge skin to said leading edge portion of said first or
said second skins, said leading edge skin hinge defining said
hinged connection.
10. The method of claim 9 wherein said step of providing said
leading edge skin hinge further comprising: providing a skin
leading edge pultrusion and a retaining pin, said leading edge
pultrusion being attached to said leading edge portion of said
first or said second skins, said leading edge skin hinge being
attached to said leading edge skin, said retaining pin releasably
attaching said leading edge pultrusion and said leading edge skin
hinge, and wherein said step of inspecting the rotor blade further
comprising: removing said leading edge skin.
11. A method of inspecting a rotor blade of a wind turbine, the
method comprising: a. providing a first skin and a second skin,
said first skin and said second skin each defining a trailing edge
portion, said trailing edge portions of said first and said second
skins having a configuration for releasable attachment one to the
other; b. providing a first spar and a second spar, said first spar
having an attachment with said first skin, said second spar having
an attachment with said second skin, said first spar having an
attachment to said second spar; c. inspecting said attachment
between said first spar and second spar; and d. releasably
attaching said trailing edge portions of said first and said second
skins.
12. The method of claim 11 wherein the rotor blade has a trailing
edge, said trailing edge being defined by said trailing edge
portions of said first and said second skins when said trailing
edge portions are releasably attached.
13. The method of claim 12, the method further comprising:
inspecting said attachment between said first skin and said first
spar and inspecting said attachment between said second skin and
said second spar prior to said step of releasably attaching said
trailing edge portions of said first and second skins.
14. The method of claim 11 wherein the rotor blade has a trailing
edge, said step of providing said first skin and said second skin
further comprising: providing a mechanical lock proximal to said
trailing edge of the rotor blade, said mechanical lock being
configured to releasably attach said trailing edge portions of said
first and second skins one to the other, said mechanical lock
defining said configuration for releasable attachment of said
trailing edge portions of said first and second skins.
15. The method of claim 14, said step of providing said mechanical
lock further comprising: providing a male portion and a female
portion defining said mechanical lock, said male portion being
attached to said trailing edge portion of a one of said first and
second skins, said female portion being attached to said trailing
edge portion of the other of said first and said second skins, said
male and said female portions of said mechanical lock being
configured to releasably attach said trailing edge portions of said
first and second skins one to the other.
16. The method of claim 15, said step of releasably attaching said
trailing edge portion of said first skin to said trailing edge
portion of said second skin comprising: releasably attaching said
male portion and said female portion of said mechanical lock.
17. The method of claim 11 wherein the rotor blade has a leading
edge, the method further comprising: providing a leading edge skin,
said leading edge skin being in a hinged connection to said leading
edge portion of a one of said first skin and said second skin, said
leading edge skin defining said leading edge of the rotor
blade.
18. The method of claim 17 wherein said step of providing said
leading edge skin further comprising: providing a leading edge skin
hinge, said leading edge skin hinge releasably attaching said
leading edge skin to said leading edge portion of said first or
said second skins, said leading edge skin hinge defining said
hinged connection.
19. The method of claim 11 wherein said first spar and said second
spar each defines a plurality of elongated ribs and wherein said
attachment between said first spar and said second spar is a shear
web, said shear web having a first shear web edge and an opposing
second shear web edge, said first shear web edge being attached to
a one of said ribs of said first spar, said second shear web edge
being attached to a one of said ribs of said second spar, said step
of inspecting said attachment between said first and second spars
comprising: inspecting said attachments of said first edge of said
shear web and said rib of said first spar and said attachment of
said second edge of said shear web and said rib of said second
spar.
Description
RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 12/757,832 filed Apr. 9, 2010 by the inventor
herein and claims priority to the prior application.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The Invention is a wind turbine rotor blade assembly for
generation of power and is a wind turbine featuring the blade. The
Invention is also a method of making the wind turbine rotor blade.
The wind turbine rotor blade of the invention is highly reliable
and inexpensive to manufacture compared to large prior-technology
wind turbine rotor blades.
[0004] 2. Description of the Related Art
[0005] Wind turbines harvest the kinetic energy of the wind and
convert that energy into shaft power at a rotating output shaft.
The rotating output shaft turns an electrical generator to produce
electrical power. For wind turbines of the horizontal type, the
blades rotate in a plane of rotation that is on the upwind side or
downwind side of a supporting tower and about an axis of rotation
that is generally horizontal with the Earth. The rotor of a
horizontal-type wind turbine for commercial electrical power
generation is large, and can be over 400 feet in diameter. The
rotor includes one or more rotor blades. Each rotor blade is shaped
as an airfoil. The wind passing over the rotating rotor blade
generates lift, impelling the rotor blade to rotate about the axis
of rotation.
[0006] A wind turbine rotor blade is subject to substantial
stresses due to the rotational inertia of the rotor and the moments
imparted by the wind and by gravity. The moments imparted by the
wind and by gravity acting on the rotor blade vary along the span
of the rotor blade and vary with each revolution of the rotor.
Gusts, variable wind speeds and inclement weather can place a very
high steady and alternating loading on the structures of a wind
turbine. Wind turbines also are subject to frequent starting and
stopping cycles. Failure of current-technology wind turbine rotor
blades is a very real problem for the wind power industry.
[0007] Fiberglass is the material of choice for wind turbine rotor
blades. During the 1970s, many materials for turbine rotor blade
construction were tried, including steel, aluminum and wood.
Turbine designers recognized degradation from fatigue as the
dominant factor in rotor blade material selection. Fiberglass has
come to dominate the industry due to its moderate density and
general resistance to degradation from fatigue.
[0008] When adopting fiberglass some thirty years ago, the wind
power industry also adopted the fiberglass construction techniques
of the time. Those techniques were developed by the small boat
industry, which was marked by low-volume production using
individual molds in which days of lay-up using multiple plys of
fiberglass were performed by hand and in which the hull or deck of
the small boat remained until the resin in the fiberglass was fully
cured. The rotor blade industry still uses these same techniques.
The vast majority (88%) of wind turbine rotor blades are
constructed by the hand lay-up of fiberglass-reinforced resin. Dry
glass fibers in the form of cloth or roving are manually placed in
forms by workers, who then infuse the dry glass fibers with resin,
either with or without the assistance of vacuum.
[0009] This non-automated prior art method of rotor blade
construction is slow, imprecise, and not conducive of high-volume
blade manufacture. Prior art wind turbine rotor blade construction
provides many opportunities for introduction of manufacturing
defects, such as improper reduction in the number of the plys of
glass fiber along the span of the blade or introduction of foreign
object debris. Prior art wind turbine rotor blade manufacture does
not allow monitoring and correction of minor defects in internal
blade components before those defects cause major blade failures.
The prior art method of blade manufacture also requires large and
expensive tooling and highly skilled labor.
[0010] Prior art turbine rotor blades feature an upper and a lower
side that are formed in molds. Upper and lower spar caps are bonded
to the upper and lower sides and are joined by shear webs that
extend the length of the blade to provide bending stiffness along
the length of the blade and to maintain the cross-sectional profile
of the blade. When the upper and lower sides of the prior art rotor
blade are joined one to the other, the leading and trailing edges
are permanently joined.
[0011] The prior art joints between the upper and lower spar caps
and the upper and lower sides and between the spar caps and the
shear web cannot be inspected once the upper and lower sides are
bonded, preventing detection of defects. A local defect, such as a
void or defect in a bond for the shear web, can propagate along the
length of the rotor blade during operation of the rotor blade,
causing catastrophic failure. The local defect generally will
translate into a rotor blade failure triggered by a precipitating
event, such as erosion, a lightning strike, a blade overload or a
tower strike.
[0012] The Piasecki Aircraft Corporation (`PiAC`) conducted a root
cause analysis of numerous rotor blade failures. The root cause
analysis concluded that factory processes and controls in the
manufacturing environment of the prior art wind turbine rotor
blades caused many of the failures. Other failures were caused by
design shortcomings of the prior art rotor blades. Among the
manufacturing defects found in the root cause analysis were dry
fiber, misaligned fiber layup, core voids and deficient ply
build-up in transition sections.
[0013] The prior art does not teach the wind turbine, the wind
turbine rotor blade, or the method of the Invention.
BRIEF DESCRIPTION OF THE INVENTION
[0014] The wind turbine rotor blade of the Invention is constructed
to allow lighter weight, lower cost, inspectable joints and more
rapid and dependable construction than prior technology wind
turbine rotor blades. The rotor blade of the Invention has a
two-part or a three-part skin. For both the two and three-part
rotor blades, opposing first and second composite skins are
preformed in molds with multiple structural forms for later
assembly. The opposing first and second composite skins may be
resin reinforced with glass or carbon fibers. For the three-part
rotor blade, a leading edge skin is rolled from stainless
steel.
[0015] Each skin is formed separately from the spar that reacts the
primary bending loads acting on the wind turbine rotor blade. The
spar extends the span, or length, of the rotor blade from the rotor
blade root to the rotor blade tip. The rotor blade root is the end
of the rotor blade that attaches to the hub of the wind turbine.
The rotor blade tip is the free end of the rotor blade. The spar is
disposed within the skins and reinforces the rotor blade so that
the rotor blade maintains its cross-sectional shape. The spar also
provides stiffness along the span of the rotor blade normal to the
plane of rotation to resist bending of the rotor blade in response
to the wind loads.
[0016] The spar features a pair of elongated spar pultrusions. Each
spar pultrusion has a spar pultrusion base and a plurality of ribs
normal to the spar pultrusion base. The spar pultrusion base of one
of the pultrusions is bonded to one of the opposing faces of the
first and second composite skins and the other spar pultrusion base
is bonded to the other of the opposing faces. The spar pultrusions
(and the ribs forming part of those spar pultrusions) extend from
the rotor blade root to the rotor blade tip.
[0017] The process of `pultrusion` is a continuous manufacturing
process for creating composite parts having a constant
cross-section and any desired length. Reinforcing fibers such as
fibers of glass or carbon are fully saturated ("wetted-out") with a
thermosetting resin, usually unsaturated polyester or a vinyl
ester. The wetted-out fibers are compacted to eliminate excess
resin and pulled through a heated die. Heat from the die cures the
resin while the composite is still fully laminated and held in the
desired shape by the die. The pultruded part is fully hardened by
the time that the part leaves the die. The part can be immediately
inspected for voids or other defects using automated systems and
defective sections immediately discarded. The term `pultrusion` as
used in this document includes a part made by the pultrusion
process.
[0018] Because the rotor blade has a smaller chord (width) at the
rotor blade tip than at the rotor blade root, and because the spar
experiences smaller flexural (bending) moments toward the tip than
toward the root, the degree of reinforcement provided by the full
width of the spar pultrusion is not required or desirable for the
full span of the rotor blade. Prior to assembly into the rotor
blade, the spar pultrusion is cut as described below. As used in
this document, the term "cut" as applied to the spar pultrusion
means cut using a water jet, cut using a saw, cut using a
platen-type "C" head water jet cutting machine, cut using a milling
machine or cut using any other apparatus or technique known in the
art.
[0019] The cutting of the spar pultrusion reduces the width of the
spar pultrusion base, and hence the number of elongated ribs, in a
stepwise fashion from the rotor blade root to the rotor blade tip.
The cutting of the spar pultrusion also can reduce the depth of
each of the remaining elongated ribs toward the rotor blade tip, so
that the depth of the reinforcing rib is greater toward the rotor
blade root and lesser toward the rotor blade tip. The cutting of
the spar pultrusion can reduce the thickness of the spar pultrusion
base and the thickness of the ribs so that the thickness of the
base and the thickness of the ribs is greater toward the blade root
and lesser toward the blade tip. The cutting of the spar pultrusion
corresponds the local strength and stiffness of the spar, and hence
the strength and stiffness of the rotor blade, to the loads that
will be placed on the rotor blade locally.
[0020] The number of elongated ribs, the rib depth, and the other
structural elements of the rotor blade are selected to be the
minimum that will carry the expected loads with an adequate factor
of safety, thereby minimizing the weight of the rotor blade.
[0021] The spar also includes a series of shear webs locally
joining a one of the spar pultrusion ribs attached to the first
skin to a corresponding spar pultrusion rib attached to the second
skin. The shear web is a composite structure with opposing shear
web skins on either side of a shear web core. The shear web skins
are strong and stiff compared with the core. For example, the shear
web skins may be glass fiber-reinforced resin and the shear web
core may be composed of foam, balsa wood or paper. The location and
dimensions of the shear web at each location along the rotor blade
are selected to accommodate the local stresses that are expected to
occur at that location. If the expected local stresses at a
location require additional longitudinal stiffness or resistance to
twisting, two or more shear webs may join two or more pairs of ribs
at the location.
[0022] The number, dimensions and locations of the shear web(s) and
ribs at each location along the span of the rotor blade may be
selected to control the local torsional stiffness (resistance to
twisting of the rotor blade in response to a load) of the rotor
blade at each location along the span of the rotor blade as well as
the strength and flexural stiffness (resistance to longitudinal
bending of the rotor blade in response to a load) of the rotor
blade at each location along the span of the rotor blade. Selecting
the local torsional stiffness of the rotor blade allows the rotor
blade to be designed to twist by a predetermined amount in response
to a given local wind loading at each location along the span of
the rotor blade. The predetermined amount of twist in response to a
given local wind load may be selected to adjust dynamically the
local angle of attack of the rotating rotor blade at each location
along the span of the rotor blade. For example, the local torsional
stiffness may be selected so that under conditions of high wind,
the rotor blade twists to reduce the angle of attack of the rotor
blade, shedding a portion of the wind load on the rotor blade and
avoiding overloading the rotor blade.
[0023] Each shear web has a first and a second edge. Each of the
first and second edge is bonded to an elongated fastening member
generally having an `H` shape in cross section. One side of the `H`
is configured to engage a rib. The other side of the `H` is
configured to engage the shear web. The elongated fastening member
is constructed using pultrusion techniques. The elongated fastening
member is connected to the appropriate rib by bonding and also by
use of pin members, which are mechanical fasteners, attaching the
elongated fastening member to the rib through holes defined by the
elongated fastening member and the rib. The term 'pin members also
includes bolts, screws, rivets or other conventional fasteners that
pass through corresponding holes to join two objects together. Pin
members may be composed of any suitable material, such as a
composite or a metal.
[0024] To construct the rotor blade of the Invention having a
three-part skin, two opposing composite skins are constructed in
molds and a leading edge skin is formed by rolling stainless steel
sheet. The embodiment of the invention having a two-part skin
dispenses with the separate leading edge skin.
[0025] Two or more pultrusions having a spar pultrusion base and
ribs normal to the spar pultrusion base are created and checked for
defects during the conventional pultrusion process. The pultrusions
are cut to reduce the width of the spar pultrusion base and hence
the number of ribs in a stepwise fashion to correspond to the
dimensions of the rotor blade and the local stresses that will be
supported by the rotor blade. The cutting also trims the depth of
the ribs for the portion of the pultrusion corresponding to the tip
of the rotor blade for the same purpose.
[0026] The bases of the spar pultrusions are bonded to the opposing
portions of the inside of the composite skins that will define the
leading edge portions of the rotor blade. The bond between the spar
pultrusions and the skins are inspected for defects, dry zones and
voids. The ribs to be joined together are placed in their design
proximity. The plurality of shear webs is installed, joining the
corresponding ribs by both bonding using a bonding agent, such as
epoxy resin, and by pin members installed through holes. The pin
members act to apply pressure to the bond line between the
pultrusion connector members and the ribs during manufacture to
achieve improved bonding. The pin members also serve as a redundant
load transfer mechanism and as a rip-stop to prevent complete
failure of the pultrusion connector-rib connection in the event of
failure of the bond.
[0027] The combination of the shear web(s) and the spar pultrusions
defines the spar.
[0028] The spar, in combination with the skins, defines the
torsional and flexural stiffness of the turbine rotor blade. The
bonds between the shear webs and the ribs are inspected for voids
and defects. For the three skin embodiment, the leading edge skin
is joined to both the first and second composite skins by hinge
latches. For the two-skin embodiment, the leading edge of the first
skin is connected directly to the leading edge of the second skin
by hinge latches. The trailing edges of the skins are joined one to
the other using conventional mechanical locks, completing the rotor
blade.
[0029] Use of one or more pultrusions each having a plurality of
ribs provides a readily controllable strength and stiffness of the
leading portion of the turbine rotor blade and allows the
reinforcements to be constructed with strict quality control and
without voids or defects. Cutting of the pultrusions allows the
strength and stiffness to be tailored to the design requirements of
the rotor blade and allows the shear web, and hence the spar, to be
located in an optimal location with respect to the opposing
skins.
[0030] The use of multiple pin members as mechanical fasteners in
addition to bonding provides for a secondary load path and a
rip-stop in case a bond connection between the shear web and the
rib should fail. Failure of a current technology bond connection
between a shear web and the current technology end caps attached to
the skins can result in a catastrophic failure of the rotor
blade.
[0031] The bond attachments of current technology wind turbine
rotor blades cannot be inspected because those bonds are formed as
the skins of the rotor blade are joined to form the finished rotor
blade. The Invention allows superior opportunity for quality
control during manufacture of the rotor blade components and allows
full inspection of every step of the rotor blade assembly process.
The bond between the pultrusion and the skins may be inspected
prior to the closure of the two rotor blade skins. The attachment
of the shear web to the ribs also may be inspected prior to closure
of the rotor blade. The Invention allows defects to be found during
the assembly process, rather than upon failure of a rotor blade in
service. The leading edge hinge latches and the trailing edge
mechanical locks form releasable attachments, so that the leading
edge skin may be removed and the trailing edge may be opened for
inspection and repair of the completed rotor blade.
[0032] In one design, the rotor blade and the spar pultrusions,
including the spar pultrusion bases and the ribs, are each 125 feet
in length. The rotor blade features a linear tapered plan form with
straight leading and trailing edges. The rotor blade has a rotor
blade root having a chord of 15 feet while the rotor blade chord at
the tip is 5.6 feet. The rotor blade has a twist of 14.degree. and
is non-linear along the span of the rotor blade. The design
rotational speed of the rotor blade is 11.5 rpm and the cut-off
wind speed is 22 meters/second.
[0033] Two rotor blades are supported by opposing ends of an
elongated hub beam that is supported by a teetering hinge. The
combination of the rotor blades and hub beam defines a rotor. The
rotor rotates about the axis of rotation. The rotor drives a
low-speed shaft that powers a speed increaser. The speed increaser
is a gear train that steps up the rotational speed and is connected
to an electrical generator. The electrical generator produces
electrical power. The rotor, teetering hinge, low speed shaft,
speed increaser and electrical generator all are housed in a
nacelle supported by the tower. The electrical power produced by
the electrical generator flows through slip rings to an electrical
load. The electrical generator may be attached to an electrical
grid and the electrical load may be a load attached to the
grid.
BRIEF DESCRIPTION OF THE DRAWINGS
[0034] FIG. 1 is a perspective view of the wind turbine of the
Invention.
[0035] FIG. 2 is a cross section of the spar pultrusion prior to
cutting.
[0036] FIG. 3 is a perspective of the spar pultrusion prior to
cutting.
[0037] FIG. 4 is a plan view of the spar pultrusion after cutting
showing the stepwise reduction in width.
[0038] FIG. 5 is a perspective view of the rotor blade of the
invention.
[0039] FIG. 6 is a perspective view of the first or second
skin.
[0040] FIG. 7 is a cross section of the rotor blade at the rotor
blade root.
[0041] FIG. 8 is a cross section of the rotor blade at 50% of the
span of the rotor blade.
[0042] FIG. 9 is a cross section of the rotor blade at 60% of the
span of the rotor blade.
[0043] FIG. 10 is a cross section of the rotor blade at 70% of the
span of the rotor blade.
[0044] FIG. 11 is a detail cross section of the shear web.
[0045] FIG. 12 is a second detail cross section of the shear
web.
[0046] FIG. 13 is a detail cross section of a leading edge skin
hinge and retaining pin.
[0047] FIG. 14 is a detail cross sections of a trailing edge
mechanical lock.
[0048] FIG. 15 is a detail cross section of a second trailing edge
mechanical lock.
[0049] FIG. 16 is a detail cross section of a third trailing edge
mechanical lock.
[0050] FIG. 17 is a flow chart of the method of the Invention.
[0051] FIG. 18 is a flow chart of the pultrusion process.
[0052] FIG. 19 is a detail cross section of an embodiment having
two spar pultrusions attached to one skin.
DESCRIPTION OF AN EMBODIMENT
[0053] As shown by FIG. 1, the wind turbine 2 of the Invention
features a tower 4 and a nacelle 6 supported by the tower 4. The
nacelle supports a rotor 8. The rotor 8 comprises a hub beam 10
that rotates about an axis or rotation 12. The rotor 8 also
includes two rotor blades 14 attached to opposing ends of the hub
beam 10. The rotor blades 14 are in the shape of an airfoil and
rotate about axis of rotation 12 in response to wind 16 flowing
past the rotor blades 14. The nacelle 6 contains a low speed shaft
18 that is turned by the rotating rotor 8, a speed increaser 20
that is turned by the low speed shaft 18, and an electrical
generator 22 that is turned by the speed increaser 20. Electrical
generator 22 has an output that feeds electricity to an electrical
load 24. The electrical generator 22 can be connected to an
electrical power distribution grid 26 and the electrical load 24
can be a load 24 on the distribution grid 26. Tower 4 supports
nacelle 6 above ground 28.
[0054] FIGS. 2 through 5 illustrate the first and second spar
pultrusion 30, 32 of the Invention. A spar pultrusion 30, 32 is a
fiber-reinforced resin composite structure manufactured by pulling
spar pultrusion fibers that are wetted-out with a spar pultrusion
thermosetting resin through a heated die having the profile of the
cross section of the desired spar pultrusion 30, 32. The heat from
the die cures the spar pultrusion thermosetting resin, resulting in
a part that is hard as soon as the part leaves the die.
Pultrusions, including the spar pultrusions 30, 32 can be made of
any length. Spar pultrusions 30, 32 are inspected using
conventional automated methods as they exit the die and parts that
have voids or other defects are immediately rejected.
[0055] FIG. 2 shows the cross section of the spar pultrusion 30, 32
as it is pulled from the die. The first and second spar pultrusions
30, 32 feature a spar pultrusion base 34 and a plurality of
elongated ribs 36. The plurality of elongated ribs are oriented
generally normal to the spar pultrusion base 34. The spar
pultrusion base 34 has a width 38 and each of the ribs has a depth
40.
[0056] FIG. 3 is a detail perspective view of a portion of the spar
pultrusion 30, 32 prior to the cutting of the spar pultrusion 30,
32 as described below. The spar pultrusion has a spar pultrusion
root end 42 and a spar pultrusion tip end 44. As the spar
pultrusion 30, 32 leaves the die, the spar pultrusion 30, 32 has a
constant cross section, as illustrated by FIG. 3.
[0057] FIG. 4 shows the spar pultrusions 30, 32 after cutting and
prior to assembly into the rotor blade 14. Prior to assembly into
the rotor blade 14, the spar pultrusion 30, 32 is cut using a
platen-type "C" head water jet cutting machine so that the width 38
of the spar pultrusion base 34, and hence the number of elongated
ribs 36, is reduced in a stepwise fashion from the root end 42 to
the tip end 44. The stepwise decrease in width 38 and hence in the
number of ribs 36 is illustrated by FIG. 4. The depth 40 of each of
the elongated ribs 36 also is reduced toward the tip end 44, so
that the depth 40 of an elongated rib 36 is greater toward the root
end 42 and lesser toward the tip end 44. For each location along
the length of the spar pultrusion 30, 32, the number of ribs 36,
the thickness of ribs 36, thickness of spar pultrusion base 34,
width 38 and depth 40 are selected to correspond to the forces,
particularly bending forces, that the rotor blade 14 is designed to
withstand.
[0058] FIG. 5 is a partial cutaway perspective view of the airfoil
14 showing one of the spar pultrusions 30, 32. Rotor blade 14 has a
rotor blade root 46, a rotor blade tip 48, a chord 50, a span 52, a
leading edge 54 and a trailing edge 56. As shown by FIG. 1, rotor
blade root 46 is attached to hub beam 10. Spar pultrusions 30, 32
extend the span 52 of the rotor blade 14 from the rotor blade root
46 to the rotor blade tip 48, with spar pultrusion root end 42
corresponding to the rotor blade root 46 and the spar pultrusion
tip 44 end corresponding to the rotor blade tip 48. The rotor blade
14 comprises a first composite skin 58, a second composite skin 60
and a leading edge skin 62.
[0059] FIG. 6 is a perspective view of second composite skin 60.
First composite skin 58 is similar. First and second composite
skins 58 and 60 are constructed separately and each is constructed
as a single unit. To construct first and second composite skins 58,
60, skin reinforcing fibers comprising dry glass fibers are
assembled using conventional automated machinery similar to the
automated construction of fabric for the clothing industry. The dry
fiberglass fibers are not laid-up by hand. The quantity and
orientation of fibers in the assembled dry glass fibers are
selected to achieve the design strength selected for the skin 58,
60 at each location on the skin 58, 60. The first and second skins
58, 60 provide a substantial portion of the strength of the
finished rotor blade 14 in torsion, and a substantial portion of
the glass fibers are oriented for torsional strength. Assembled dry
glass fiber is placed in molds along with reinforcing foam,
end-grain balsa wood or other suitable materials and vacuum-infused
with skin resin using conventional techniques. The cured skins 58,
60 are removed from the molds and trimmed using automated
equipment. Composite skins 58, 60 each has an inside surface 64, a
composite skin root end 66 and a composite skin tip end 68.
Composite skin root end 66 of first and second composite skins 58,
60 define the rotor blade root 46. Composite skin tip end 68 of
first and second composite skins 58, 60 define the rotor blade tip
48.
[0060] FIGS. 7 through 10 are rotor blade 14 cross sections at
different locations along span 52 of rotor blade 14. FIG. 7 is a
cross section of rotor blade 14 at the rotor blade root 46. The
spar pultrusion base 34 of first spar pultrusion 30 is bonded to
the inside surface 64 of first composite skin 58. The spar
pultrusion base 34 of second spar pultrusion 32 is bonded to the
inside surface 64 of the second composite skin 58. Both first and
second spar pultrusions 30, 32 are located near the leading edge 54
of rotor blade 14. First and second spar pultrusions 30, 32 each
has an elongated dimension 70 (FIG. 4) that is oriented in the
direction of the span 52 of the rotor blade 14. Ribs 36 also are
oriented in the direction of span 52. Spar pultrusion base 34
provides a large bonding area with the inside surfaces 64 of first
and second composite skins 58, 60 to resist failure of the
attachments between spar pultrusion bases 34 and inside surfaces
64.
[0061] At least one shear web 72 connects one rib 36 of first spar
pultrusion 30 to a corresponding rib 36 of second spar pultrusion
32. Shear web 72 in combination with ribs 36 provides stiffness to
rotor blade 14 to resist bending of rotor blade 14 normal to the
plane of rotation due to the force of the wind 16. FIG. 7 shows a
second shear web 72 connecting another rib 36 of the first spar
pultrusion 30 to a corresponding rib 36 of the second spar
pultrusion 32. The combination of the shear webs 72 and the first
and second spar pultrusions 30, 32 define a spar.
[0062] Because the number of ribs 36 is reduced in a step-wise
fashion from the rotor blade root 46 to the rotor blade tip 48, the
shear webs 72 generally are not continuous from the rotor blade
root 46 to the rotor blade tip 48. While a shear web 72 may be
continuous for the span 52 of the rotor blade 14, a plurality of
shear webs 72 that are shorter than the span 52 attach the most
appropriate corresponding ribs 36 at each location along the span
52.
[0063] FIGS. 8, 9 and 10 are cross sections of the rotor blade 14
at 50%, 60% and 70% along the span 52 of the rotor blade 14,
respectively. Each shows first and second composite skins 58, 60.
Each shows first and second spar pultrusions 30, 32 joined to
inside surfaces 64 of first and second composite skins 58, 60.
[0064] As shown by FIGS. 7-10, the rib 36 count reduces with
increasing radius along the span 52 due to the step-wise reduction
in width 38 of spar pultrusions 30, 32. For this embodiment, at the
rotor blade root 46 shown by FIG. 7, a total of six ribs 36 are
provided on each of the first and second spar pultrusions 30, 32 to
give adequate stiffness. As shown by FIG. 8, by 50% of the span 52,
the number of ribs 36 is reduced to four on each of the first and
second spar pultrusions 30, 32 to give adequate stiffness. As shown
by FIG. 9, at 60% of the span 52, two ribs 36 are provided on first
span pultrusion 30 and three ribs 36 are provided on second span
pultrusion 32. As shown by FIG. 10, at 70% of the span 52, one rib
36 is provided on first span pultrusion 30 and two ribs 36 are
provided on second span pultrusion 32. The number, location and
depth 40 of ribs 36 are selected to provide the stiffness
required.
[0065] As shown by FIGS. 7-10, a thickness and fiber orientation is
selected for first and second spar pultrusion base 34 to allow base
34 to conform to the curved inside surfaces 64 of skins 58, 60.
[0066] FIGS. 11 and 12 are detail cross sections of the attachment
of a shear web 72 to a rib 36. The shear web 72 has a first shear
web edge 74 and an opposing second shear web edge 76. The shear web
72 also has a first shear web skin 78 and a second shear web skin
80 bonded to opposing sides of a shear web core 82.
[0067] An first connector pultrusion 84 having an H-shaped cross
section is bonded to the first shear web edge 74 and to a rib 36 of
the first spar pultrusion 30. A similar second connector pultrusion
86 is bonded to the second shear web edge 76 and to a rib 36 of the
second spar pultrusion 32. The first and second connector
pultrusions 84, 86 are manufactured from a connector reinforcing
fiber and connector thermoset resin using pultrusion technology as
discussed above.
[0068] The first and second connector pultrusions 84, 86 are
elongated and extend the length of each shear web 72. To provide a
second load path and a rip-stop in the event that a bond between
the connector pultrusions 84, 86 and ribs 36 should fail, a series
of holes 88 communicates through each connector pultrusion 84, 86
and the corresponding rib 36 to which the connector pultrusion 84,
86 is bonded. A pin member 90 is disposed within each hole 88,
mechanically clamping the attachment between the connector
pultrusions 84, 86 and the ribs 36. The plurality of pin members 90
prevents failure of a bond from spreading.
[0069] The leading edge skin 62 is shown by FIGS. 7-10 and 13. The
leading edge skin 62 is rolled from stainless steel and extends
from the rotor blade root 46 to the rotor blade tip 48. Releasable
attachments 92 join the leading edge skin 62 to the first composite
skin 58 and the second composite skin 60. From FIG. 13, the
releasable attachment 92 comprises a composite skin leading edge
pultrusion 94, a leading edge skin hinge 96 and a retaining pin 98.
The composite skin leading edge pultrusion 94 is bonded to the
leading edge side of the first and the second composite skins 58,
60. The leading edge skin hinge 96 and the composite skin leading
edge pultrusion 94 are maintained in engagement by retaining pin
98. Leading edge skin 62 may be removed from engagement with the
first and second composite skins 58, 60 by removing retaining pins
98, allowing inspection of the interior of the rotor blade 14
including the shear webs 72 and the first and second spar
pultrusions 30, 32.
[0070] Trailing edge 56 is illustrated by FIGS. 14 through 16.
FIGS. 14 and 15 are detail cross sections of the trailing edge 56.
First and second composite skins 58, 60 each defines a trailing
edge portion 100 proximal to trailing edge 56. A mechanical lock
102 defines a releasable engagement of the first and second
composite skins 58, 60 at the trailing edge portion 102. The
mechanical lock 102 features a male portion pultrusion 104 and a
female portion pultrusion 106. The male and female portion
pultrusions 104, 106 are manufactured using pultrusion technology,
as described above. The male and female portion pultrusions 104,
106 are bonded to opposing inside surfaces 64 of first and second
composite skins 58, 60. Male and female portion pultrusions 104,
106 releasably engage one with the other to form the releasable
engagement. FIGS. 14 and 15 illustrate two different embodiments of
mechanical lock 102.
[0071] FIG. 16 is cross section of the rotor blade 14 looking
toward the trailing edge 56 in a direction parallel to the chord
50. Male and female portions 104, 106 of mechanical lock 102 define
periodic openings 108 to facilitate selectable engagement and
disengagement of male and female portions 104, 106.
[0072] FIG. 17 is a flow chart of the method of the Invention. From
step 112, first and second spar pultrusions 30, 32 are manufactured
using pultrusion technology. Spar pultrusion fibers 146 such as
fibers of glass or carbon are wetted-out with a spar pultrusion
resin 148, which is usually unsaturated polyester or a vinyl ester
thermosetting resin. The wetted-out fibers are compacted to
eliminate excess resin and pulled through a heated spar pultrusion
die. The cross section of the spar pultrusion die is illustrated by
FIG. 2, which is the cross section of both the die opening and the
spar pultrusion exiting the die. As discussed above with respect to
FIG. 2, the spar pultrusion has a spar pultrusion base 34 having a
width 38. A plurality of ribs 36 are integral to the base 34 and
extend generally normal to the base 34. The base and the ribs are
elongated and have an elongated dimension 70, illustrated by FIG.
4.
[0073] For step 114, each of the first and second spar pultrusions
is cut as described above relating to FIG. 4 to reduce the width 38
of each spar pultrusion and hence the number of ribs in a step-wise
fashion from the spar pultrusion root end 42 to the spar pultrusion
tip end 44. The first and second spar pultrusion 30, 32 also are
cut to reduce the depth 40 of the ribs 36 from the root end 42 to
the tip end 44.
[0074] For step 116, first and second composite skins 58, 60 are
created as described above and comprise a skin resin 144 and a skin
reinforcing fiber 142. Each of the first and second composite skins
58, 60 has a longitudinal dimension 118 (FIG. 6) and a leading edge
portion 120.
[0075] For steps 122 through 128, the first and second composite
skins 58, 60 are joined one to the other by a shear webs 72
attaching corresponding ribs 36 of the first and second spar
pultrusions 30, 32. As described above relating to FIGS. 11 and 12,
the shear web 72 features connector pultrusions 84, 86 attached to
opposing edges 74, 76 of the shear web 72. The connector
pultrusions comprise a connector pultrusion thermoset resin 150 and
a connector pultrusion reinforcing fiber 152. The first connector
pultrusion 84 is attached to a rib 36 of the first spar pultrusion
30 by a first connector bond 134, shown by FIG. 12. The second
connector pultrusion 86 is attached to a corresponding rib 36 of
the second spar pultrusion by a second connector bond 136, shown by
FIG. 11. First and second connector bonds 134, 136 may be formed by
any suitable bonding agent, such as a thermosetting resin.
[0076] To provide a rip-stop and a secondary load path, first and
second connector pultrusions 84, 86 also are attached to ribs 36 by
a plurality of holes 88 drilled through the first and second
connector pultrusions 84, 86 and the ribs 36 to which those
connector pultrusions 84, 86 are bonded. A pin member 90 is
disposed within each hole.
[0077] Step 130 provides a step that is not possible using current
technology wind turbine construction techniques. In step 130, the
first connector bond 134 and the second connector bond 136 are
inspected after the bonds 134, 136 are created and prior closing
the composite skins 58, 60 to form the finished rotor blade 14. Any
defects can be identified and corrected during construction to
prevent failure of the rotor blade 14 in operation.
[0078] In step 132, the leading edge skin 62 is fabricated and
releasably attached to the leading edge portion 112 of the first
and second skins 58, 60, defining leading edge 54 of rotor blade
14. Trailing edge portions 100 of first and second composite skins
58, 60 are releasably joined one to the other to define trailing
edge 56 of rotor blade.
[0079] FIG. 18 illustrates the steps of the continuous pultrusion
process. In step 134, a reinforcing fiber is wetted-out; that is,
saturated, with a thermosetting resin. The reinforcing fiber may be
a spar pultrusion reinforcing fiber, a connector reinforcing fiber
or a skin reinforcing fiber. The thermosetting resin may be a spar
pultrusion thermoset resin, a connector pultrusion thermoset resin
or a skin resin. The reinforcing fibers and thermoset resin may be
any suitable fiber and suitable resin for the component to be
pultruded. As indicated by steps 136-140, the wetted-out fibers are
pulled through a pultrusion die and heated, curing the resin into a
hardened part by the time that the fiber and resin leave the
die.
[0080] FIG. 19 illustrates an embodiment having more than one spar
pultrusion attached to one skin. As shown by FIG. 19, two spar
pultrusions 30 each having a base 34 are bonded to the first skin
58 or the second skin 60. Two adjacent ribs 36 of the two spar
pultrusions 30 each are bonded to a connector pultrusion 84, 86.
The two adjacent ribs 36 also are connected to connector pultrusion
84, 86 by pin members 90. The connector pultrusion 84, 86 is bonded
to shear web 72.
LIST OF CLAIM ELEMENTS
[0081] The following is a list of elements appearing in the Claims
and the element numbers to which those elements are referred to in
the Specification and in the drawings. The elements are presented
generally in the order in which they appear in the Claims. [0082]
an rotor blade 14 [0083] a leading edge 54 [0084] a trailing edge
56 [0085] a rotor blade root 46 [0086] a rotor blade tip 48 [0087]
a chord 50 [0088] a span 52 [0089] a first composite skin 58 [0090]
a second composite skin 60 [0091] an inside surface 64 [0092] a
composite skin root end 66 [0093] a composite skin tip end 68
[0094] a first spar 30 [0095] a second spar 32 [0096] a spar base
34 [0097] a plurality of elongated ribs 36 [0098] a spar root end
42 [0099] a spar tip end 44 [0100] at least one shear web 72 [0101]
a first shear web edge 74 [0102] an opposing second shear web edge
76 [0103] an elongated dimension 70 [0104] a width 38 [0105] a spar
reinforcing fiber 142 [0106] a spar thermoset resin 144 [0107] a
depth 40 [0108] a first shear web skin 78 [0109] a second shear web
skin 80 [0110] a shear web core 82 [0111] a first shear web edge 74
[0112] a second shear web edge 76 [0113] a first connector 84
[0114] a second connector 86 [0115] a connector thermoset resin 150
[0116] a connector reinforcing fiber 152 [0117] pin members 90
[0118] holes 88 [0119] a leading edge skin 62 [0120] a releasable
attachment 92 [0121] a composite skin hinge 94 [0122] a leading
edge skin hinge 96 [0123] a retaining pin 98 [0124] a trailing edge
portion (of the first and second composite skins) 100 [0125] a
releasable attachment 92 [0126] a mechanical lock 102 [0127] a male
portion 104 [0128] a female portion 106 [0129] a tower 4 [0130] an
electrical generator 22 [0131] a ground 28 [0132] a turbine rotor
blade 14 [0133] an axis of rotation 12 [0134] a composite skin root
66 [0135] a composite skin tip 68 [0136] a skin reinforcing fiber
142 [0137] a skin resin 144 [0138] a longitudinal dimension (of
skins) 110 [0139] a pultrusion die 138 [0140] an elongated
dimension 70 [0141] a leading edge portion of said first skin 112
[0142] a leading edge portion of said second skin 112 [0143]
cutting each said spar pultrusion to reduce said spar base width
114 [0144] cutting said ribs to reduce said depth 114 [0145] a
first elongated connector bond 134 [0146] a second elongated
connector bond 136 [0147] inspecting said first elongated connector
bond 130 [0148] inspecting said second elongated connector bond 130
[0149] inspecting said pin members 130
* * * * *