Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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ECONOMIC LOW-HEAD HYDRO AND TIDAL POWER TURBINE
FIELD OF INVENTION:
This invention relates to reaction turbines for low-head hydro and tidal power
applications.
BACKGROUND OF THE INVENTION:
Devices which take advantage of the energy in falling water have existed for
several
centuries. The earliest example is the water wheel. It is an impulse device
which uses a multitude
of buckets or paddles to catch falling or moving water, depositing it at a
downstream point. The
movement of the buckets or paddles spins a central supporting shaft which can
do work or be used
to generate power.
In the late 1800's and early 1900's hydro power innovators discovered the
advantages of
reaction turbines, which mainly generate power from pressure and energy
differences in stream flow.
These turbines extract more power from streams than water wheels, rotate at
higher speeds and
accept much larger water flow volumes. Reaction turbines, such as the Francis
or Kaplan, are
therefore almost exclusively used at high flow hydroelectric sites. Both of
these designs utilize a
rotating disc of blades oriented in a plane perpendicular to the direction of
exit flow. Impulse hydro
power generating devices are still used in high-head (over 20m) low-flow
applications (the Pelton
design) and low-head (3m to lOm) low-flow applications (Cross-flow design).
The Francis, Kaplan, Pelton and Cross-flow hydro power designs are mature
technologies
and very well understood. None of these designs, however, is recommended for
high-flow
applications of less then 3 meters of head. The impulse designs cannot accept
very large water flows
while the Francis and Kaplan turbines are not practical. To utilize these
large reaction turbines at
low-head sites they must be partially elevated resulting in very low water
pressures. Cavitation can
result damaging the turbines and water transport surfaces. Variations on the
Kaplan, such as the
Starflow, inclined Kaplan and Bulb turbines, all of which are similar to water
flowing through a
propeller, have been recommended for low-head situations, however, they are
not economical for
heads of less than 3m and many rivers with higher heads and lesser flows.
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One solution for economically generating power from ultra-low-head hydro sites
(less than
3m of head) is adoption of the Darrieus turbine design. The Darrieus turbine
was developed in
France by Georges Darrieus in the 1920's to generate power from wind. It
consists of a set of long,
rectangular airfoils connected to a central rotating shaft. The airfoils may
be curved to directly
connect to the shaft or be straight and held parallel to the shaft by struts,
arms or discs. Significant
testing in the 1980's and 1990's demonstrated the utility of this turbine
design. Darrieus turbines
were, however, not widely adopted for wind power as pinwheel type wind
turbines were more
economical.
In the early 1980's a Canadian innovator, Barry V. Davis, applied the vertical-
axis Darrieus
design to water. Several different models were successfully tested in the
laboratory and various
waterways. Government funding ended in the late 1980's, however, several
organizations are
presently attempting to utilize the Davis turbine design in ultra-low-head
hydro and tidal
applications.
While the Davis turbine demonstrates the applicability of the Darrieus design
in water, there
are two key drawbacks. The first is rotation about the vertical axis. To
extract the power from a
wide ultra-low-head river many Davis turbines located side by side would be
required. This
increases the quantity of moving parts, gears and generators, resulting in
increased complexity and
cost. The second problem is torque pulsation. Unlike a propeller type turbine
which receives fluid
flow energy uniformly over time, Darrieus type turbines have spikes and
troughs in energy imparted
by the fluid. Torque on the rotating shaft peaks when a blade spins directly
perpendicular to the
direction of fluid flow and drops until the following blade approaches the
point of peak torque.
Power generators cannot be easily connected to turbines with pulsating torque.
A solution to the torque pulsation problem is disclosed by Alexander M. Gorlov
in U.S.
Patent 6,036,443 and Canadian Patent 2222115. The Gorlov turbine is similar to
the Darrieus
turbine, however the airfoil blades are curved into a helix at a constant
diameter from the central
rotating shaft, resulting in constant torque over time. While the Gorlov
turbine is an innovative
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solution, it requires the construction helix type blades which are costly and
complex relative to flat
rectangular Darrieus airfoil blades. In addition, the complexity of helix
blade construction makes
the turbine much more susceptible to fabrication errors which can result in
premature failure.
OBJECTS OF THE INVENTION:
It is an object of this invention to provide a simple, reliable and low-cost
reaction turbine
system for generating smooth non-pulsating power from ultra-low-head hydro or
tidal flow sites.
SUMMARY OF THE INVENTION:
The present invention, which satisfies the foregoing objects, is a reaction
turbine system
consisting of several Darrieus type turbines connected in series along a
single rotating shaft. In the
invention's simplest form a long shaft is elevated at its ends by two
supports. The supports permit
rotation of the shaft and orient the longitudinal axis of the shaft
horizontally and perpendicular to
the direction of fluid flow. Three blade support discs are connected at their
rotational centres to the
shaft. The face of each disc is perpendicular to the longitudinal axis of the
shaft. The leftmost
Darrieus turbine module consists of four wing-like turbine blades extended
between the leftmost and
centre discs. Each blade is parallel to the shaft and has a constant tear-drop
airfoil profile along its
longitudinal axis. The four blades are all equidistant from the shaft and
dispersed at 90 degree
intervals around the shaft. A similar set of four blades extends between the
centre and rightmost
discs, making a second Darrieus turbine module. The only difference is that
the blades are offset 45
degrees from the blades in the leftmost Darrieus turbine module. The quantity
of Darrieus turbine
modules and number of blades can be varied to meet the economics, energy
conversion efficiency
and shaft rotational speed requirements for a particular site.
The offsetting of blades between adjacent Darrieus turbine modules greatly
reduces or
eliminates the torque pulsation effect. While a simple horizontally oriented
Darrieus turbine with
four blades pulsates four times per rotation, a turbine system with two offset
Darrieus turbine
modules of four blades each pulsates eight times per rotation, smoothing out
the pulsation effect and
reducing the magnitude of each pulsation. Utilizing three sections would
create 12 even smaller
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pulsations per rotation. With enough blades and / or modules the blades would
cover the turbine
system's circle of rotation, providing smooth torque and rotation. The complex
and more expensive
helical blades of the Gorlov turbine would not be required.
The invention is easily scalable and therefore more simple and economic than
the Davis
turbine. For example, to utilize the invention in a wide river the only
adjustment is longer blade
sections and / or a greater number of Darrieus turbine modules. As always, a
single shaft, power
generator and gearing system (if necessary) are required. In contrast, an
equivalent Davis turbine
system requires a multitude of vertical shafts, gears, generators and
electrical systems, resulting in
increased cost and complexity. Additional support structures are also
necessary, increasing flow
turbulence and decreasing energy conversion efficiency.
The invention is also more economic and practical than a horizontally oriented
Darrieus
turbine with a large number of blades. The Darrieus turbine has a higher
number of blades per unit
width than the invention and is therefore more costly. The greater blade
density also reduces
rotational speed, increasing the cost of gearing between the shaft and
generator. This is a significant
factor in megawatt installations. Besides the cost disadvantages, a Darrieus
turbine with a large
number of blades still experiences torque pulsation. To minimize the effect a
very large blade
density is required, but water flow through the turbine will become choked and
overly turbulent.
Turbine efficiency is greatly reduced. A Darrieus turbine with 100% blade
coverage is a cylinder,
will not function and is not an option.
The invention can be placed in any area of unidirectional or bi-directional
flow, such as a
river, channel, duct or tidal zone. In low-head hydro applications best
results are obtained by placing
the Darrieus turbine modules in a fluid flow duct. The duct forces all the
flow through the bladed
area allowing the system to exceed the Betz limit of energy conversion
efficiency (59.3%) for
turbines in open fluid flow. Efficiencies approaching that of traditional
reaction turbines are
theoretically possible. The invention is also useful in tidal zones as the
Darrieus turbine modules
generate power from any flow perpendicular to the longitudinal axis of the
shaft, such as tidal
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inflows and outflows. Power is generated by connecting a generator or gearing
system and generator
to either end of the shaft or any portion of the shaft not within any of the
Darrieus turbine modules.
BRIEF DESCRIPTION OF THE DRAWINGS:
The invention can be better understood by reference to the accompanying
drawings in which:
Figure 1 is a frontal view of the reaction turbine system down the direction
of fluid flow,
according to the present invention;
Figure 2 is a frontal view of a Darrieus turbine module down the direction of
fluid flow,
according to the present invention;
Figure 3 is a cross-sectional view of the Darrieus turbine module in Figure 2;
Figure 4 is a cross-sectional view of the two Darrieus turbine modules in
series in Figure 1;
Figure 5 is a frontal view down the direction of flow of the reaction turbine
system with an
additional shaft support separating the Darrieus turbine modules, according to
another embodiment
of the present invention;
Figure 6 is a frontal view down the direction of flow of a Darrieus turbine
module with a
discontinuity in the shaft, according to another embodiment of the present
invention;
Figure 7 is a cross-sectional view of the Darrieus turbine module in Figure 6;
Figure 8 is a frontal view of the reaction turbine system wherein the Darrieus
turbine modules
are enclosed by fluid flow duct, according to another embodiment of the
present invention; and
Figure 9 is cross-sectional view of the reaction turbine system in Figure 8 at
the leftmost
Darrieus turbine section.
DETAILED DESCRIPTION OF THE DRAWINGS:
Figure 1 is a frontal view down the direction of fluid flow for one embodiment
of the
invention. Shaft supports 1 elevate a shaft 2 and permit its rotation. The
longitudinal axis of the
shaft 2 is horizontal and perpendicular to the direction of fluid flow. In
this embodiment two
Darrieus turbine modules 9, further described in Figure 2, are connected to
the shaft 2. Fluid flow
through the reaction turbine system rotates the Darrieus turbine modules 9
which in turn rotate the
shaft 2. A generator, gearing system and generator, or belt system and
generator (none of which are
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shown) can be connected to either end of the rotating shaft to generate
electric power.
Figure 2 is a frontal view down the direction of fluid flow of a Darrieus
turbine module 9.
The Darrieus turbine module 9 consists of two blade support members 4 and a
set of wing-like airfoil
blades 3. A blade support member 4 can be a disc, radial spokes or any other
blade support
mechanism known in the art. Each blade 3 has a long rectangular profile
between the two blade
support members 4 and a constant teardrop airfoil cross-section along its
longitudinal axis, as shown
in Figure 3. A blade 3 can be constructed from a solid and non-flexible
material such as metal,
aluminum or reinforced polymer. The fluid flowing past each blade 3 creates
lift and some drag,
rotating the Darrieus turbine module 9. The shaft 2, which passes through the
centre of each blade
support member 4, is thereby rotated.
Figure 3, the cross-sectional view of Figure 2, helps explain rotation of a
Darrieus turbine
module 9. Each blade 3 is mounted parallel to the shaft 2 and equidistant from
the shaft 2, resulting
in a circle of rotation 6 about the shaft. The chord of each airfoil generally
forms a chord on an arc
of the circle of rotation 6. In this embodiment the blades 3 are spaced
equally around the circle of
rotation 6. This provides for the smoothest production of power. Any number of
blades may be
provided, depending on energy conversion efficiency and shaft 2 rotation speed
requirements.
Adding blades 3 increases energy conversion efficiency but reduces shaft 2
rotational speed.
Conversely, eliminating blades 3 reduces energy conversion efficiency but
increases shaft 2
rotational speed. Adding too many blades 3 can choke fluid flow, create excess
turbulence and
reduce energy conversion efficiency.
Fluid flow in the direction of arrows 5 causes the Darrieus turbine module 9
in Figure 3 to
rotate clockwise. Fluid flow from the opposite direction will also cause
clockwise rotation. In
general, rotation of a Darrieus turbine module 9 will be from the tails of the
airfoils 3 towards their
noses. Maximum energy is imparted from the fluid flow when the chord of the
leading blade 3 is
perpendicular to the direction of flow 5. As one blade 3 leaves the maximum
energy position and
the next blade 3 moves towards it, energy imparted to the system decreases and
increases. This
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creates the torque pulsation common to simple Darrieus turbines.
To eliminate or significantly reduce this pulsation effect the invention
utilizes multiple
Darrieus turbine modules 9 connected in series along a single shaft 2. The
blades 3 in each Darrieus
turbine module 9 are offset from the blades 3 in adjacent Darrieus turbine
modules 9. This
effectively multiplies the number of blades 3 which pass through the maximum
energy zone during
each rotation of the system. Figure 4, a cross-section of the Darrieus turbine
modules 9 in Figure
1, demonstrates this effect. Where a single Darrieus turbine module 9 presents
only four blades 3
per rotation, as in Figure 3, two Darrieus turbine modules 9 present eight
blades 3 per rotation as in
Figure 4. If required, additional blades 3 and / or Darrieus turbine sections
9 may be added to fully
cover the circle of rotation 6 with blades. Such an arrangement would produce
perfectly smooth
rotation, torque and power. This is essential for connection to a power
generator.
Figure 5 is an embodiment of the invention wherein a central shaft support 7
located between
Darrieus turbine modules 9 helps elevate the shaft 2. Such a central shaft
support 7 might be
necessary when the span between shaft supports 1 is too wide for the shaft 2
to support its weight.
If more than two Darrieus turbine modules 3 are used, multiple central shaft
supports 7 are an option.
A central shaft support 7 can also be used to connect the shaft 2 to a
generator or gearing system and
generator.
In a further embodiment of the invention, the central shaft 2 is discontinued
within the span
of one or more Darrieus turbine modules 9. Figure 6 is a frontal view down the
direction of fluid
flow of such a Darrieus turbine module 9. Figure 7 is the cross-sectional view
of Figure 6 at the
inside face of the rightmost blade support member 4. The Darrieus turbine
module is exactly the
same as in Figures 2 and 3 except that the shaft 2 is removed from the fluid
flow area between blade
support members 4. Less turbulence and higher energy conversion efficiency
results. The Darrieus
turbine module 9 imparts rotation to the shaft 2 by either being directly
connected to the shaft 2 at
one or both outside faces of its blade support members 4, or by being
indirectly connected to the
shaft 2 through other Darrieus turbine modules 9.
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In an open fluid flow area some flow will pass around the reaction turbine
system, imparting
no energy. Figure 8 is a frontal view down the direction of flow of an
embodiment of the invention
wherein a duct 8 minimizes this loss of flow. Figure 9 is a cross-section of
Figure 8 at the leftmost
Darrieus turbine module 9. In this embodiment the Darrieus turbine modules 9
are surrounded by
a duct 8 which forces almost all the flow through the blades 3. The smaller
the minimum gap
between duct 8 walls and the blades 3, the higher the energy conversion
efficiency. If Darrieus
turbine modules 9 are not adjacent to each other, a separate duct 8 for each
non-adjacent Darrieus
turbine module 9 is an option.
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