Note: Descriptions are shown in the official language in which they were submitted.
CA 02549376 2006-06-22
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CA 02549376 2006-06-22
WO 2006/029496 PCT/CA2005/000267
and high cycle fatigue, particularly as without an inner support ring the
blades are
cantilevered towards the centre of the unit from the housing.
United States Patent RE38,336E (Reissue of 5,592,816) to Williams
discloseZi a hydroelectric turbine with a central open area of unrestricted
flow
S surrounded by the blades which proposed reducing down current turbulence.
United
States Patent 6,648,58982, also to Williams, disclosed a hydroelectric turbine
with a
central open area of unrestricted flow surrounded by the blades to aid in
increasing
the velocity of the water flowing through the single blade and to eliminate
the
turbulence that occurs behind the hub in traditional hub generator
hydroelectric
turbines. The Williams patents employ complicated hydraulic and mechanically
driven generators with a uni-directional turbine blade configuration without
ducting
nor hydrodynamic structures to direct water flow in an efficient manner. The
Williams patents do not incorporate a set of bearings at the hub to improve
the
structural integrity of the unit and reduce blade deflection.
The present invention satisfies the need for a structurally and mechanically
simple and inexpensive to manufacture flow enhancement design which increases
water flow, provides a bypass for sea life and debris thereby reducing the
environmental impact of the unit, reduces vibration and hydrodynamic drag and
increases the operating efficiency of underwater ducted turbines.
3. SUMMARY OF THE INVENTION
It is an object of the present invention to implement an improved hydro
turbine generator and method of flow enhancement wherein the improvement
comprises a slot between a duct or housing and an augmentor device which is
disposed about the duct. The augmentor device optimally has an inlet and an
outlet
which are substantially similar in area and a narrower central throat portion,
thereby
increasing the efficiency of the turbine. Specific optimal ratios of the
throat area,
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slot area and the blade area to the inlet area are disclosed which further
optimize the
efficiency of the turbine.
The augmentor may be partial, or a complete second duct disposed about
substantially all of the outer surface of the first duct, thereby creating a
dual duct
S structure.
Another object of the present invention is to provide an augmentor which is
axi-symmetric, with leading edges having hydrodynamic profiles, thereby
minimizing turbulent water flow past the inlet and outlet and performing
optimally in
bi-directional water flow. The dual duct structure may be coated with an anti-
fouling coating and may include buoyancy material, thereby achieving greater
noise
suppression, ensuring minimal environmental impact and providing corrosion
resistance and high lubricity.
Another object of the present invention is to provide a flow enhancement
structure in a turbine comprising a longitudinal hole substantially along the
longitudinal axis of the turbine in a hub having specific shape, structural
and material
characteristics, thereby improving the efficiency of the turbine. Specific
ratios of the
hole area to the blade area are disclosed. The hole, combined with the flow
characteristics of the hub, renders the turbine safe in relation to marine
life.
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4
4. BRIEF DESCRIPTION OF THE DRAWINGS
The apparatus and method of the present invention will now be described
with reference to the accompanying drawing figures, in which:
FIG. 1 is an isometric view of the dual augmentor duct underwater turbine
generator with slot and hollow hub flow enhancement structures according to
the
invention.
FIG. 2 is a front elevation view of the dual duct underwater turbine generator
with slot and hollow hub flow enhancement structures according to the
invention.
FIG. 3 is a cut-away perspective view of the dual augmentor duct underwater
turbine generator with slot and hollow hub flow enhancement structures
according to
the invention.
FIG. 4 is a side elevation sectional view of the hub and outer and augmentor
ducts defining the slot and hole and showing flow streamlines according to the
invention.
FIG. 5 is a side elevation detail view of the leading edges of the hollow hub
and outer augmentor ducts.
FIG. 6 is a side elevation sectional view of a dual augmentor duct open slot
variation of the invention.
FIG. 7 is a side elevation sectional view of a cylindrical dual augmentor duct
slot variation of the invention.
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5. DETAILED DESCRIPTION OF THE INVENTION
Referring to Figure 1, an isometric view of the dual augmentor duct
5 underwater turbine generator 10 with slot 200 and hollow hub 240 flow
enhancement
structures of the preferred embodiment is shown. In the preferred embodiment,
the
underwater ducted turbine 10 is of the type disclosed in the applicants'
earlier
invention the subject of PCT/CA02/01413 application to Davis et al., with the
present improvement being directed towards a hollow hub 20 design and second,
augmentor duct 41 disposed about the outer duct 40 with a slot 200 between the
two
ducts 43, which together enhance water flow 100 and increase efficiency of the
turbine generator 10. The dual augmentor duct structure 43 is a fore and aft
symmetric structure, namely it is symmetrical about a central vertical plane
which
transacts the turbine generator 10 laterally. The dual duct structure 43 is
disposed
1 S about the turbine rotor 50 and all generator components which are housed
in the
outer duct 40. The augmentor duct 41 has symmetrical inlet portions 45 and 46
creating a highly efficient duct for bi-directional flow. The central hole 240
may
also be employed in units 10 without a hub, for instance with cantilevered
blades
disposed radially towards a central portion of the turbine generator. The
central hole
240 may also be employed in non-ducted turbine generators 10.
The dual duct structure 43 is secured to the hub 20 by a plurality of struts
24
which also act as guide vanes in the annulus 51 area. The struts 24 are merely
struts
in the slot 200 area and not curved guide vanes. In the preferred embodiment
there
are five guide vanes 24 at each of the two ends of the turbine generator 10.
The
vanes 24 are preferably evenly spaced radially about the hub 20 axis. In the
preferred embodiment, two counter-rotating rotor disks 50 are rotatably
attached to
the hub 20 and a plurality of blades 30, optimally symmetric hydrofoil blades,
extend
radially from said hub 20 to a rotor rim 54 which seats in a groove (not
shown) in the
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6
interior surface of the outer duct 40 and is rotatable in a bearing race, or
in a
variation, a magnet bearing race. In other variations, single or multiple
rotor disks
50 may be employed. The flow enhancement slot 200 and hole 240 structures may
be employed not only for tidal applications, but also for other turbine
generation
applications, as one skilled in the art can appreciate.
In the preferred embodiment the dual augmentor duct 43 is. a rigid structure
manufactured from composite material. The dual augmentor duct 43 may be made
from any composite material such as fiberglass, KevlarTM, carbon fiber, fiber-
reinforced concrete or any other combination known in the art. Advantages of
the
rigid, symmetrical dual duct 43 arrangement include simplicity of manufacture,
installation and maintenance and low capital cost. In a variation, a stainless
steel
rigid frame covered by a flexible composite material is used.
The interior wall of the augmentor duct 41 diverges towards the augmentor
duct rim 62, thereby producing a decelerating effect downstream of the turbine
blades as the water 100 flows through the duct 20. The outer surface of the
augmentor duct 41 is concave in the preferred embodiment, but may be convex or
cylindrical. Both ends of the dual augmentor duct 43 are effectively inlets as
the
turbine generator 10 is bidirectional. The central portion of the augmentor
duct 41,
is cylindrical. In operation, water flow 100 converges as it passes the inlet
rim 62
and follows the profile of the augmentor duct 41 and outer duct 40. The gap or
slot
200 between the outer duct 40 and augmentor ducts 41 is a smooth annular flow
area. The blade tips 30 and rotor rim 54 (not shown here) are contained in
annulus 51
and are not disposed in the slot 200. After the water flow 100 passes the
rotor disks
50, the outer duct 40 and augmentor duct 41 diverge again, to allow for the
smooth
diffusion of the water flow 100 back to free stream conditions. The symmetry
of the
dual augmentor duct 43 achieves high hydraulic efficiencies in a bi-
directional tidal
environment. In the preferred embodiment, the duct entry 45 and exit 46 are
axi-
symmetric. Alternate configurations such as square, rectangular or any other
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arbitrary shape may be employed as dictated by the parameters of specific
sites or
applications such as tidal regime and local bathymetry. The optimal shape for
each
site is determined by performing a computational fluid dynamic analysis of the
site.
The preferred embodiment, however, is axi-symmetric.
The optimal design is further characterized by an inlet area 45 (augmentor
duct rim 62) equal to the exit area 46 (opposite augmentor duct rim 62) and a
throat
area, turbine blade area, or annulus 51 (cylindrical section) that is
optimally between
nine-tenths (0.9) to one quarter (0.25) of the exit area 46 depending on the
site-
specific tidal conditions. The annulus 51 is the area between the inner
surface of the
outer duct 40 and the outer surface of the hub 20 through which the turbine
blades 30
pass. In the preferred embodiment, for general applications, the ratio of the
central
throat or inner surface of the outer duct 40 central portion to the augmentor
duct rim
62 diameter is 0.5. In variations the ratio may be between 0.1 and 0.9.
The leading and trailing edges or rims of both ducts 43 (including outer duct
40 rim 64) optimally have a hydrodynamic profile with a cross section that is
similar
in shape to an airplane wing. This profile increases the flow 100 into the
turbine
armulus as well as creates a smooth transition of the flow 100 into the
adjacent slot
200 and around the entire tidal turbine generator 10.
In the preferred embodiment, an anti-fouling coating, such as Si-Coat 560TM,
is applied to the ducts 43. In a variation, specific areas susceptible to the
buildup of
aquatic organisms are coated. The anti-foul coating has the additional benefit
of
providing a high lubricity surface which facilitates laminar flow, thereby
improving
the efficiency of the turbine generator 10.
Buoyancy material is incorporated into the internal structure of the dual
augmentor duct 43 and the generator housing 92 in order to increase the
overall
buoyancy of the tidal turbine generator 10. Neutral buoyancy is a key
characteristic
of the unit as it facilitates the process of unit removal and maintenance. In
the
preferred embodiment, the ducts 43 are comprised of a composite shell
structure
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filled with poly vinyl chloride closed cell marine foam (not shown) in order
to
achieve neutral buoyancy for the entire tidal turbine generator 10. Other
closed cell
foams, as known in the art, may also be employed. In addition to the buoyancy
function, the closed cell foam acts as a noise suppression device by
attenuating the
hydrodynamic and electrical noise produced by the tidal generator 10, thus
mitigating any possible acoustic impacts of the tidal turbine generator 10 on
cetaceans and other marine mammals.
The second unique flow characteristic is a longitudinal hole 240 through the
hub 20. The inner surface of the hub 20 is optimally cylindrical. The outer
surface
of the hub is optimally elliptical, or barrel shaped, rising from the hub rim
27 to an
apex in the flat central portion of the hub 20. The inner surface of the hub
20 defines
the longitudinal hole 240 along the hub 20 axis. In other variations, the
profiles are
varied as determined by a computational fluid dynamic analysis of the specific
tidal
site.
Referring now to Figure 2, a front elevation view of the dual augmentor duct
underwater turbine generator with slot 200 and hollow hub 240 flow enhancement
structure is shown. The leading edge of the outer duct rim 64, hub rim 27,
curved
nature of the guide vanes 24 in the preferred embodiment, followed by the
blades 30
and surrounded by the outer duct 40 are shown.
Now refernng to Figure 3, a cut away perspective view of the slot 200
through the tidal turbine generator 10 is shown. The slot 200 is defined by an
upper
surface, which is formed by the inner surface of the augmentor duct 41, and a
lower
surface formed by the outer surface of the outer duct 40, which encloses the
generator housing 92. The augmentor duct 41 is comprised of an inlet area 45,
throat
area 47 and exit area 46, which reverse with each flow 100 reversal. The lower
surface of the slot 200, in the preferred embodiment, is cylindrical with
leading edge
or outer duct rim 64 providing a smooth entry for the water flow 100 into both
the
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slot 200 and the turbine annulus or rotor disk area 51. The blades 30 are
disposed in
a rotor rim or ring 54.
In variations, depending on the results from specific computational fluid
dynamics ("CFD") analyses, the contours of the slot surface 200 may be varied.
The
leading 34 and trailing 35 edges have a hydrodynamic profile with a cross
section
that is similar in shape to an airplane wing. This edge profile increases the
flow 100
into the annulus area 51 as well as creates a smooth transition of the flow
100 into
the central opening 240.
The central hole 240 is a region where the conservation of fluid momentum is
maintained. This feature both eliminates the region of separation that
previously
existed behind the hub 20, and in addition, draws additional flow 100 through
the
surrounding turbine rotor disk area 51. Elimination of the region of
separation also
reduces the vibratory loading on the structure 10 resulting in improved
reliability and
therefore reduced maintenance cost.
This central hole 240 increases both the output torque, and therefore the
overall efficiency of the tidal turbine 10.
The central hole 240 concept also has a positive environmental benefit in
addition to its performance enhancing effects. This central region 240
provides a
fish and marine mammal bypass in the event that this sea life enters the tidal
turbine
generator 10. The hole 240 through the centre is large enough to accommodate
all
types of fish, and the majority of other marine mammals (with the exclusion of
large
whales).
The area occupied by the central hole 240 is less than or equal to the area
occupied by the turbine rotor disk S 1. The exact ratio of these areas is
determined by
CFD analysis performed using site-specific parameters. The optimal hole 240 to
turbine rotor disk area 51 ratio is between 1:15 and 1:1, but in variations
other ratios
may be employed to some advantage.
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The hub 20 that defines the central hole 240 is an integral structural member
of the tidal turbine generator 10. The radial load or force on~the turbine 10
is
transferred from the hub 20 to the guide vanes or struts 24 and then through
to the
primary structural member, the outer duct 40. This produces a very stiff and
robust
5 structure. The hub 20 houses a series of bearings 58 that provide the
principal radial
alignment and thrust support for the turbine rotor 50. Water lubricated, ldw
friction
bearings 58 are mounted at the turbine rotor hub 20. A central journal bearing
58 (or
bearings) provides radial support for the rotor 50 and two thrust bearings 58
are
located on either side of the rotor 50 to accommodate axial excursions
resulting from
10 the bi-directional hydrodynamic load on the turbine 10. An additional set
of water
lubricated bearings 58 is also employed at the blade (rotor ) rim 54 location
to
counteract the axial thrust load of the rotor 50. This complete bearing
arrangement
58 reduces the susceptibility of the turbine rotor SO to racking. Optionally,
a
magnetic bearing system or any other bearing system that is well known in the
art
can be employed.
In the preferred embodiment, the hub 20 consists of marine grade stainless
steel. An alternate embodiment includes a hub 20 manufactured from a composite
material such as fiberglass, KevlarTM, Carbon fiber or any combination known
in the
art.
Referring now to Figure 4, a side elevation sectional view of the hub and
outer and augmentor ducts defining the slot and hole and showing flow
streamlines
102 is shown. The flow streamlines 102 illustrate the flow enhancement
features of
this design. In variations, the geometry of the profile is varied in order to
improve
the flow characteristics for site-specific installations. The slot 200
geometry is a
function of the characteristics of the tidal stream at the specific site;
however, the slot
area 200, or effective gap has a normal range of 10% - 50% of the turbine
rotor area
or annulus 51. Figure 4 illustrates the deflection of the flow streamlines 102
from
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11
the hole 240 and slot 200 area into the annulus 51, thereby increasing the
flow onto
the rotor 50 and thereby increasing the power output.
The fluid that enters the slot 200 maintains its momentum through the slot
200 and then imparts this momentum into the boundary layer of the diverging
section
of the dual augmentor duct 43. This injection of fluid has the effect of both
delaying
the region of separation on the divergent portion of the duct 43 as well as
drawing
additional flow through the enclosed annulus 51 area. The net result of these
effects
is a significant increase in performance in blade 30 torque, and therefore an
overall.
efficiency improvement of the tidal turbine generator 10.
Now referring to Figure 5, a side elevation detail view of the leading edges
of
the hollow hub and outer and augmentor ducts is shown. The elliptical, fluid
dynamic shape of the hub 20 rim 27, outer duct 40 rim 64, and the augmentor
duct
41 rim 62, promote laminar flow and generator efficiency. The slot 200 and
hole
240 are also shown.
Now refernng to Figure 6, a side elevation sectional view of a dual duct with
an open slot variation is shown. The slot 200 is discontinuous, and each
augmentor
duct rim 62 is supported by the struts 24. The water flow 100 is also shown.
Now refernng to Figure 7, a side elevation sectional view of a dual
cylindrical duct covered slot 200 variation of the invention is shown. The
outer
surface of the outer duct 40 is cylindrical in this variation.
In operation, the reduced vibrational loading on the tidal turbine generator
10,
smoother laminar flow, increased water flow 100 through the rotor disks 50 due
to
the slot 200 and hole 240 features increase the output torque of the rotor
disk SO by
above 50% in comparison to a similar turbine generator without the above-
described
flow enhancement structure, depending on the unit 10 type and site parameters,
which in turn translates into an overall efficiency improvement of greater
than 10%.
As will be apparent to those skilled in the art in light of the foregoing
disclosure, many alterations and modifications are possible in the practice of
this
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12
invention without departing from the spirit or scope thereof. Accordingly, the
scope
of the invention is to be construed in accordance with the substance defined
by the
following claims.
