U.S. patent application number 10/473224 was filed with the patent office on 2004-05-20 for system for a turbine with a gaseous or liquideous working medium.
Invention is credited to Engstrom, Staffan.
Application Number | 20040096329 10/473224 |
Document ID | / |
Family ID | 20283619 |
Filed Date | 2004-05-20 |
United States Patent
Application |
20040096329 |
Kind Code |
A1 |
Engstrom, Staffan |
May 20, 2004 |
System for a turbine with a gaseous or liquideous working
medium
Abstract
This invention relates to a system for a turbine with a gaseous
or liquideous working medium, in particular a wind turbine for a
wind turbine generator. The turbine comprises a shaft (3), which is
rotatable at a certain angular frequency, a hub (2), on which at
least one turbine blade (1) is attached, and a hinge member (12,
13) disposed between said shaft (3) and hub (2). The hinge member
comprises a bearing (12) and spring elements (13), together forming
a rigidity (k) against movements in the hinge member (12, 13). The
turbine blade (1) has a mass inertia factor relatively to the hinge
member (12, 13) and is adapted to move through said gaseous or
liquideous flow, which has a flow direction essentially
perpendicular to the rotational plane of said turbine blade (1),
and has a varying flow velocity in said direction such that the
system is exposed to disturbance forces. An essential component of
the disturbance forces has a disturbance frequency
(.OMEGA..sub.disturbance) which is composed of said angular
frequency (.OMEGA..sub.rotation) and the rigidity (k) of said hinge
member (12, 13), the mass inertia factor (J.sub.turbine) of said
turbine blade (1) and the angular frequency (.OMEGA..sub.rotation)
of said shaft (3) in the system has been selected such that the
system is supercritical or subcritical. The invention also related
to a wind turbine generator with such a system.
Inventors: |
Engstrom, Staffan; (Lidingo,
SE) |
Correspondence
Address: |
YOUNG & THOMPSON
745 SOUTH 23RD STREET 2ND FLOOR
ARLINGTON
VA
22202
|
Family ID: |
20283619 |
Appl. No.: |
10/473224 |
Filed: |
September 29, 2003 |
PCT Filed: |
March 28, 2002 |
PCT NO: |
PCT/SE02/00619 |
Current U.S.
Class: |
416/132B |
Current CPC
Class: |
Y02E 10/721 20130101;
Y02E 10/72 20130101; F03D 1/0658 20130101 |
Class at
Publication: |
416/132.00B |
International
Class: |
F01D 005/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 30, 2001 |
SE |
0101150-1 |
Claims
1. A turbine adapted for a gaseous or liquideous working medium, in
particular a wind turbine for a wind turbine generator, comprising
a shaft (3), which is rotatable at a certain angular frequency
(.omega..sub.rotation), a hub (2), on which at least one turbine
blade (1) is attached, and a hinge member (12, 13) disposed between
said shaft (3) and said hub (2) and comprising a bearing (12) and
spring elements (13), together forming a rigidity (k) against
movements in the hinge member (12, 13), said turbine blade (1)
having a mass inertia factor (J.sub.turbine) relatively to the
hinge member (12, 13) and being adapted to move through said
gaseous or liquideous flow, which has a flow direction essentially
perpendicular to the rotational plane of said turbine blade (1),
and has a varying flow velocity in this direction, such that the
turbine is exposed to disturbance forces whose essential component
has a disturbance frequency (.omega..sub.disturbance) which is
composed of said angular frequency (.omega..sub.rotation), and that
said hinge member (12, 13) forms a teeter hinge having an
eigenfrequency (.omega..sub.resonance), that is calculated at
.omega..sub.resonance={squ- are root}{square root over
(k.sup.iJturbin)}, characterised in that the rigidity (k) of said
hinge member (12, 13), the mass inertia factor (J.sub.turbine) of
said turbine blade (1) and the angular frequency
(.omega..sub.rotation) have been selected such that the condition
.omega..sub.rotation.noteq.{square root}{square root over
(k/Jturbin)} is fulfilled.
2. A turbine according to claim 1, characterised in that the ratio
of the angular frequency (.omega..sub.rotation) to the
eigenfrequency of the teeter hinge (.omega..sub.resonance) is 0.9
at most.
3. A turbine according to claim 2, characterised in that the ratio
of the angular frequency (.omega..sub.rotation) to the
eigenfrequency of the teeter hinge (.omega..sub.resonance) is at
least 0.1.
4. A turbine according to claim 3, characterised in that the ratio
of the angular frequency (.omega..sub.rotation) to the
eigenfrequency of the teeter hinge (.omega..sub.resonance) is at
least 1.1.
5. A turbine according to claim 4, characterised in that the ratio
of the angular frequency (.omega..sub.rotation) to the
eigenfrequency of the teeter hinge (.omega..sub.resonance) is 10.0
at most.
6. A turbine according to any one of the preceding claims,
characterised in that said hinge member (12, 13) includes
dampers.
7. A turbine according to any one of the preceding claims,
characterised in that said spring elements (13) are
progressive.
8. A turbine according to any one of the preceding claims,
characterised in that said spring elements (13) are
pre-stressed.
9. A wind turbine generator with a turbine according to any one of
the preceding claims.
10. A method to design a turbine adapted for a gaseous or
liquideous working medium, in particular a wind turbine for a wind
turbine generator, said turbine comprising a shaft (3), which is
rotatable at a certain angular frequency (.omega..sub.rotation), a
hub (2), on which at least one turbine blade (1) is attached, and a
hinge member (12, 13) disposed between said shaft (3) and said hub
(2) and comprising a bearing (12) and spring elements (13),
together forming a rigidity (k) against movements in the hinge
member (12, 13), said turbine blade (1) having a mass inertia
factor (J.sub.turbine) relatively to the hinge member (12, 13) and
being adapted to move through said gaseous or liquideous flow,
which has a flow direction essentially perpendicular to the
rotational plane of said turbine blade (1) and has a varying flow
velocity in this direction, such that the turbine is exposed to
disturbance forces whose essential component has a disturbance
frequency (.omega..sub.disturbance) which is composed of said
angular frequency (.omega..sub.rotation), and that said hinge
member (12, 13) forms a teeter hinge having an eigenfrequency
(.omega..sub.resonance) , that is calculated at
.omega..sub.resonance={square root}{square root over (k/Jturbin)},
characterised in that the rigidity (k) of said hinge member (12,
13), the mass inertia factor (J.sub.turbine) of said turbine blade
(1), and the angular frequency (.omega..sub.rotation) are selected
such that the condition .omega..sub.rotation.noteq.{square
root}{square root over (k/Jturbin)} is fulfilled.
11. A method according to claim 10, characterised in that the
rigidity (k) of said hinge (12, 13) is selected such that the
condition .omega..sub.rotation.noteq.{square root}{square root over
(k/Jturbin)} is fulfilled at normal angular frequency
(.omega..sub.rotation).
Description
FIELD OF THE INVENTION
[0001] The invention relates to a system for a turbine with a
gaseous or liquideous working medium, in particular a wind turbine
for a wind turbine generator. The turbine comprises a shaft, which
is rotatable at a certain angular frequency, a hub, on which at
least one turbine blade is attached, and a hinge member, disposed
between the shaft and the hub. The hinge member comprises a bearing
and spring elements, together forming a rigidity against movements
in the hinge member. The turbine blade has a mass inertia factor
relatively to the hinge member and is adapted to move through the
gaseous or liquideous flow, which has a flow direction essentially
perpendicular to the rotational plane of said turbine blade and has
a varying velocity in said direction, such that the system is
exposed to disturbance forces. The invention also relates to a wind
turbine generator with such a system.
BACKGROUND OF THE INVENTION
[0002] Conventionally, wind turbine generators have rigid hubs,
which means that the blades of the wind turbine have a rigid
connection with the hub. The function in acceptable when the number
of blades is at least three, since three symmetrically arranged
blades, to a certain extent, are capable of levelling out the
imbalance forces that are created due to irregularities in the wind
field. A reduction of the number of blades to two is desirable,
since this means a considerable reduction of the blade cost as well
as other advantages, such as a less complicated assembly. The
yearly energy yield for the two-bladed turbine, calculated for a
certain turbine diameter, is only reduced with 2-3%. However, a
two-bladed, rigid hub wind turbine is exposed to considerable
imbalance forces even during normal operation causing fatigue in
the components of the turbine. This must be compensated by
increased dimensions of all the main components, such that this
two-bladed solution, due to the excessive cost, is no longer
justified. As a consequence, this type of wind turbine is no longer
manufactured.
[0003] The teetered hub became the solution of the problems of the
two-bladed, rigid hub wind turbine. It is characterised by the two
blades being rigidly fixed to a hub, which is hinged to the turbine
shaft. U.S. Pat. No. 4,565,929 discloses an example of a turbine,
which is able to teeter .+-.7.degree. until making contact with the
teeter stops. The function is satisfactory during normal
conditions, which means that the fatigue behaviour is advantageous.
However, during extreme wind conditions with high turbulence and
wind shear, such contacts with the teeter stops may occur that
result in more severe moments than in a rigid hub wind turbine.
Thus, it is the extreme load cases that are critical. None of the
turbines with this simple type of teeter hub have reached any
widespread use.
[0004] In order to solve the problems caused by the extreme loads,
it has been proposed to control the teeter movement by combining
the teeter stops with damping. One example is disclosed in U.S.
Pat. No. 5,354,175, in which it is proposed to limit the teeter
movement by a controllable hydraulic damping. None of these hub
types have been used extensively, which is due to a lack of
knowledge of how a hub should be designed in order to prevent a
serious increase of the disturbance forces in the system under
certain conditions.
BASIC IDEA OF THE INVENTION
[0005] The object of the present invention is to provide a system
for a turbine, in particular a system for a wind turbine for a wind
turbine generator, which minimises the effects of the imbalance
forces caused by the irregularities in the wind field, and thus the
risk of fatigue, and of the extreme loads in the structure.
[0006] The invention is based on the understanding that a wind
turbine, e.g. a two bladed wind turbine, with a teeter hinge having
a certain rigidity, in theory may be looked upon as a mass-spring
system according to classical mechanics.
[0007] The wind field comprises both a systematic variation, wind
shear, which means that the mean wind speed is higher during the
upper part of the revolution of the turbine, and a stochastic
variation, turbulence. It is obvious that the wind shear creates
one load cycle for each revolution of the turbine in a, with the
turbine, co-rotating system of coordinates. Also the less
significant tower shadow (the air stream that is disturbed by the
tower), creates the same variation. On further consideration it
should be realised that also the turbulence will create components
of the same frequency, since the turbine blades move swiftly
(50-100 m/s) compared with the wind (about 5-25 m/s) and its
irregularities. Each turbine blade will thus hit a specific
irregularity of the wind several times, which means that the
resulting disturbance also in this case will have a frequency
.omega..sub.disturbance which is equal to the rotational angular
frequency .omega..sub.rotation, i.e.
.omega..sub.disturbance=.omega..sub.rotation (1)
[0008] In the following this frequency is denominated the
disturbance frequency.
[0009] It should be noted that this condition is valid in a, with
the turbine, co-rotating system of co-ordinates, which is relevant
for those forces that affect the turbine. In a system of
co-ordinates that is fixed to the nacelle or tower the disturbance
frequency is proportional to the result of the multiplication of
the number of blades and the rotational frequency.
[0010] The majority of today's wind turbines operate at a
rotational speed (angular frequency), which normally varies with a
few per cent, depending on the slip of the inductor generator
generally used. This value may increase up to about ten per cent
with a special generator design. Instead of fixed speed, the wind
turbine operates within a rotational speed range. There are also
generators with dual windings which operate within two different
rotational speed ranges. It is possible to control the rotational
speed to any value, usually a low at low wind speeds and a high at
high wind speeds, by applying specific electric equipment. The
rotational angular frequency of the turbine .omega..sub.rotation
shall be construed in the present invention as the highest
rotational speed range which is used during normal, main circuit
connected operation. This is possible since the high rotational
speeds normally is used when the wind speeds are fairly high or
high and the wind turbine has a high output power, which constitute
the operation conditions that are decisive for the dimensioning of
the turbine.
[0011] The mass inertia factor of the turbine J.sub.turbine
relatively to the teeter axis may be calculated. The contribution
from the hub, however, is insignificant. Thus, the mass inertia
factor of the turbine may be approximated as the mass inertia
factor of the blades. The hinge member is assumed to be of the
type, in which the movement is counteracted by springs, which makes
it possible to calculate a spring constant k for the hinge member.
The spring constant constitutes a value of the rigidity of the
hinge member. According to classic mechanics, the eigenfrequency
.omega..sub.resonance of the turbine in relation to the hinge may
be calculated as
.omega..sub.resonance={overscore (k/Jturbin )} (2)
[0012] From now on this is called the eigenfrequency of the teeter
hinge. It should be noted that, for clarity, the stabilising impact
on teeter movements of the centrifugal force, i.e. increase of
rigidity due to the centrifugal force, has not been analysed
here.
[0013] In order to elucidate the general reaction of such a
mass-spring-system on disturbances of varying frequencies, the
amplification, i.e. the ratio of the amplitude of the system to the
amplitude of the disturbance, has been studied. A moderate damping
has been added to the system, in correspondence with an actual
state in which the air will dampen the teetering movement of the
blades and the hinge member may be furnished with damping
elements.
[0014] The study reveals that a low disturbance frequency
.omega..sub.disturbance in relation to the eigenfrequency of the
teeter hinge .omega..sub.resonance, i.e. the operation is
subcritical according to classical mechanics, gives a system
response that is slightly larger than the disturbance, i.e. the
amplification is just exceeding 1, corresponding to an ideal hub
with a relatively high degree of rigidity. It is further revealed
that the amplification is large when the disturbing frequency and
the eigenfrequency of the system are equal, i.e. the operation is
critical. It is likely that earlier attempts to use teetering hubs
with counteracting springs have given this effect. When the
disturbing frequency is higher than the eigenfrequency, i.e. the
operation is supercritical, the amplification is significantly
lower.
[0015] The cases mentioned above illustrate the conditions during
normal operation. A wind turbine with a teeter hinge having a
certain rigidity additionally has the advantage that the states
during extreme turbulence and wind shear, which happen a few times
during the operational life of a wind turbine, can be handled with
reasonable loads and teeter angles.
[0016] The conditions during normal operation primarily determine
the fatigue of the materials of the structure, while the extreme
operation states are decisive for the extreme loads. A hub with a
certain rigidity presents an improved balance between the fatigue
load cases and the extreme load cases.
[0017] The study as described above illustrates that operation in
the range of large amplification of the disturbance, i.e. when the
disturbing frequency and the eigenfrequency are equal, should be
avoided. These results have been confirmed by simulations in the
time domain with a reasonably comprehensive computer turbine model,
said model correctly taking mass distribution, stationary and
instationary aerodynamics, hinges, rigidity, damping, wind
distribution, increase of rigidity due to the centrifugal force,
etc, into consideration for wind turbines at different wind speeds.
The simulations has revealed that the moment in the hub becomes as
much as ten times larger when the rigidity of the hub has the
critical value as compared with a higher or lower value.
[0018] As mentioned above, the degree of criticality depends on the
relations between the disturbing frequency, the mass inertia factor
of the turbine and the rigidity of the teeter hinge. In the
construction phase, these values may be selected without
restrictions. The disturbing frequency is equal to the rotational
speed. The mass inertia factor of the turbine is mainly determined
by the mass distribution and by the geometry of the blades. For a
specific blade geometry, the mass inertia factor may be influenced
by the choice of construction materials and by adding ballast
material. The rigidity of the teeter hinge is determined by the
stiffness of the different hinge elements, which normally are made
of rubber or some other elastomeric material. Thus, it is
relatively easy to change the rigidity, also in an existing teeter
hinge, by exchanging the rubber elements to new ones with a
different Young's modulus and possibly with a modified
geometry.
[0019] To summerize, in accordance with the invention, the hub is
constructed such that the operation is either supercritical or
subcritical. By putting the invention into practise, the loads
decrease considerably and both technical and economical advantages
are achieved.
SHORT DESCRIPTION OF THE DRAWINGS
[0020] The invention will be further described in detail below with
reference to the appended drawings, in which
[0021] FIG. 1 illustrates how a system consisting of a mass, a
spring and a damper in general reacts on disturbances of different
frequencies,
[0022] FIG. 2 shows the principal structure of a wind turbine
generator with a horizontal axis wind turbine,
[0023] FIG. 3A shows a side elevation, partly as a sectional view,
of a teeter hub according to the invention and FIG. 3B shows the
teeter hub as shown in FIG. 3A in a front elevation view.
DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
[0024] FIG. 1 illustrates how a system consisting of a mass, a
spring and a damper in general reacts on disturbances of different
frequencies. The amplification (Y-direction in FIG. 1), i.e. the
ratio of the amplitude of the system to the amplitude of the
disturbance, is shown as a function of the ratio of the disturbing
frequency to the eigenfrequency of the system (X-direction in FIG.
1). Point A indicates a state in which the disturbing frequency
.omega..sub.disturbance is low relatively to the eigenfrequency of
the teeter hinge .omega..sub.resonance, i.e. the operation is
subcritical according to classical mechanics, corresponding to an
ideal hub with a relatively high degree of rigidity. The response
is slightly larger than the disturbance, i.e. the amplification is
slightly larger than 1. In point B, the disturbing frequency and
the eigenfrequency are equal, i.e. the operation is critical. The
amplification of the disturbance is large. Point C indicates a
state in which the disturbing frequency is higher than the
eigenfrequency, i.e. the operation is supercritical. The response
is lower than in point A and significantly lower than in point
B.
[0025] FIG. 1 illustrates that operation in the range of point B,
in which there is a significant amplification of the disturbance,
should be avoided.
[0026] FIG. 2 shows the general structure of a wind turbine
generator with a horizontal axis wind turbine. Two aerodynamically
shaped turbine blades (1) are connected to the hub (2) with a fixed
or pivotal (along the longitudinal axis) connection. The hub (2) is
connected to the turbine shaft (3), which is supported by the
bearings (4). The turbine shaft (3) is connected to the gearbox
(5), which transforms the low rotation speed of the turbine to a
rotation speed conformable to the generator (6). The components of
the machinery are supported by the machinery bed (7), which is
connected to the yaw bearing (8). The yaw bearing (8) is rotatable
on the tower (10) by means of the yaw mechanism (9). The tower is
connected to solid ground by a foundation (not shown). The various
functions may be more or less integrated with each other, which
however does not affect the following description.
[0027] In FIG. 2 is indicated that the hub (2) is a teetered hub,
which implies that the two turbine blades (1) are rigidly connected
to the hub (2). The hub (2) is hinged to the turbine shaft (3) and
may teeter an angle A, as shown, in each direction.
[0028] The number of blades is normally two, but in one preferred
embodiment the structure principle is applied to a turbine with one
blade, and with the missing blade compensated by a counter
weight.
[0029] FIG. 3 shows a teeter hub according to the invention. As
above, the blades (1) are connected to the hub (2), which normally
is a cast structure and is connected to the turbine shaft (3) by
means of a hinge member. The hinge member includes a bearing (12),
which normally is composed of two or four symmetrically disposed
bearing elements. The spring elements (13) counteract the teeter
movement and may be combined with dampers, either by selecting a
spring material with some damping properties, or by providing
dampers of some other type (not shown). The active part of both the
bearing (12) and the spring elements (13) are preferably made of
elastomeric material.
[0030] The bearing (12) and the spring elements (13) together form
a hinge member (12,13) having a specific rigidity in relation to
the axis of the hinge member and hence the bearing. In a preferred
embodiment, the bearing (12) and the spring elements (13) have been
integrated into one unit, e.g. a so-called flex-beam. In this case,
as well as when neighbouring components (primarily the turbine
blades) have some inherent softness, the spring constant of the
spring elements (13) may include the impact of these elements.
[0031] In preferred embodiments additional advantages may be
achieved by making the spring (13) progressive (i.e. the spring
constant increases with the dimensional change) or pre-stressed. A
special type of progressive spring is achieved when there is a play
between the spring element and the co-acting element, which results
in a spring constant that is zero during the initial part of the
teeter movement.
[0032] As described above, the structural parameters should by
selected such that operation is avoided in the range in which the
disturbing frequency is close to the critical frequency, i.e. the
eigenfrequency of the teeter hinge. In preferred embodiments, the
parameters are selected such that the disturbing frequency either
is lower than 0.9 times the eigenfrequency or higher than 1.1 times
the eigenfrequency. In addition, according to preferred
embodiments, the disturbing frequency is normally higher than 0.1
times the eigenfrequency and lower than 10 times the
eigenfrequency. Thus, the range between 0.1 and 0.9 times the
eigenfrequency generates especially interesting preferred
embodiments, in view of the requirements to avoid large extreme
loads as described above.
[0033] As described above, the invention and the preferred
embodiments of the invention as described imply essential technical
and economical advantages when applied on one- and two-bladed wind
turbine generators in particular.
[0034] Preferred embodiments as described above illustrate how the
invention may be applied on wind turbines with one or two blades.
However, the man skilled in the art may easily apply the invention
on wind turbines with several blades and on neighbouring
application areas, such as propellers for airplanes and ships,
fans, turbines for other gaseous or liquideous working media,
etc.
* * * * *