Note: Descriptions are shown in the official language in which they were submitted.
CA 02677016 2009-08-28
Double Drag Wind Rotor
[01] The present invention of a Wind Collector, (hereinafter referred to as
the "Drag
Rotor"), relates generally to renewable energy systems, and more specifically,
to wind turbine and energy conversion systems. The main area relates to the
Wind Power Industry whereas embodiments of the invention improve the design
of a wind rotor for collection of medium range wind energy of 10 kilo Watts
(kW)
to 1 mega Watt (mW). Because the Drag Rotor is based on the usage of Drag
forces (that oppose the relative motion of an object through a fluid: a liquid
or a
gas) the invention also relates largely to aerodynamics.
Background of the Invention
a) Physics - Aerodynamics
[02] When a rotor is designed as a "drag" device to operate behind the wind,
then
the orientation (i.e. angle to the wind), the speed of the wind and the shape
of
the wind rotor mean that the drag coefficient (i.e. a dimensionless quantity
which
is used to quantify the drag or resistance of an object in a fluid environment
such as air or water) becomes a major factor and can vary from 0.01 up to 2.5.
The following are sample drag coefficients for some well known structures.
Drag coefficients examples
Mercedes 300SE (class E) 0.785 11 Empire State Building 1.3 - 1.5
Square 'Ram-Air' Parachute 2.2-2.99
Eiffel Tower 1.8-2.0
1
CA 02677016 2009-08-28
[03] Conversely to "lift type" rotors, the maximum efficiency of a drag rotor
is
obtained when the drag coefficient is as large as possible. With a drag type
wind
rotor, using a vertical axis maximizes the drag coefficient and the conversion
of
the wind force as a torque results in the direct application of the drag
equation:
1
PU2 CD A,
FD -
where
FD is the force of drag, which is by definition the force component in the
direction of the flow velocity
p is the mass density of the fluid
u is the velocity of the object relative to the fluid
A is the reference area
Co is the drag coefficient - a dimensionless constant
[04] When perpendicular to the wind, certain shapes of drag type produce
higher
drag coefficients than others:
Sphere [0.40
Hollow semi-sphere opposite stream 0.38
Hollow semi-sphere facing stream 1.42
Hollow semi-cylinder opposite stream 1.20
I 11
Hollow semi-cylinder facing stream 2.30
Squared flat plate at 90 IE1
Long flat plate at 90 1.98
Open Wheel, rotating 0.58
2
CA 02677016 2009-08-28
[05] Wind Rotors function as transformers of the kinetic wind power in
rotational
motion and may have horizontal or vertical axis. Drag Rotors generating up to
1
mW, not having to convert perpendicularly the direction of the wind flow to
generate a rotary motion, are better as they may collect about twice more of
the
energy contained in the wind than HAWT (Horizontal Axis Wind Turbine) using a
propeller. Also, they are able to work at slower speeds.
b) Conventional Wind Rotors - Propellers
[06] With conventional three blade wind rotors (called `Lift Type' Rotors),
the
propellers use the "lift" effect to make the blades turn, and therefore only
the
"induced lift drag" may improve the rendering ratio of the device where any
other
form of drag impedes performance and should be reduced as much as possible.
(See Figure 2a)
[07] Furthermore, conventional wind rotors face additional problems because
they
generally have a horizontal axis (except Darrieus models, which are VAWT -
See Figure 3) and being lift type, they deflect the wind, even before the wind
reaches the rotor plane. (see Figure 2c)
[08] Therefore they are inefficient in capturing the energy in the wind, due
to:
= several laws of physics (i.e. Betz law which reduces their capacity to
collect
the power of the wind at only 16/27);
= the fact they convert the wind energy into a perpendicularly rotary motion,
which divides the collectable results by one half (See Figure 2b); and
= their design and weight means that they do not even start to turn until wind
speeds of 4.5 to 5 meters per second (m/s), and do not produce any
significant power until wind speeds of 8 to 12 m/s are raised, and by design
of conventional wind technology do not capture additional, usable wind
energy with winds over 12.5 m/s.
3
CA 02677016 2009-08-28
c) Savonius Rotors
[09] The Savonius wind rotors (See figure 3a) are a type of VAWT, used for
converting the power of the wind into torque on a vertical rotating shaft.
Aerodynamically, they are also drag-type devices, consisting of two or three
scoops. Looking down on a Savonius Rotor from above, a two-scoop machine
would look like an "S" shape in cross section (See Figure 3b). Because of the
curvature, the scoops experience less drag when moving against the wind (i.e.
drag coefficient Cd2 = 1.2) than when moving with the wind (i.e. drag
coefficient
Cdl= 2.3). The differential drag being positive, it causes Savonius turbines
to
spin. Because they are limited by such differential, Savonius turbines extract
less of the wind's power than other similarly-sized lift-type turbines but
work
better with low wind speeds.
Summary of the Invention
a) Power collectable from the wind
[10] The table below shows the power contained in the wind compared to its
speed
and the maximum recoverable power for conventional wind rotors and Savonius
Rotors compared to the Drag Rotor:
m/s 2 4 6 8 10 12 14 16 18 20 22
Kinetic Power / m2
W/m2 5 39 132 314 613 1,058 1,681 2,509 3,572 4,900 6,522
3 blade conventional wind rotor
0.236 1 9 31 74 145 250 397 592 843 1,156 1, 539
Savonius rotor
0.65 3 25 86 204 399 689 1096 1635 2328 3194 4251
`Double Drag' rotors
0.8 4 31 106 251 490 846 1,345 2,007 2,858 3,920 5,218
4
CA 02677016 2009-08-28
[1] The Kinetic Power in the wind for an airfoil A (in m2), with a wind speed
u
(in m/s) and a density p (in kg/m3) is given by:
PKin= j*p*A*u3
Where p = 1,23 kg/m3 at 15 C and with atmospheric pressure of
1,0132 bar
[2] The maximum recoverable power for a conventional wind rotor (with
propeller) is:
PMax=PKin * 16/27*K*Cp
Where the Betz factor = 16/27, K represents the Rendering Ratio of
the propeller's shape (considered here as 80%) and Cp = Efficiency
Coefficient of the propeller < 0.5
PMax = 0.8 * 0.296 Pwn
[3] For Savonius rotors, considering the drag coefficient differential of a
hollow
semi-cylinder facing & opposite stream, an ideal rotor would recover:
PMax = PKin * ACD = 16/27 * (2.3 - 1.2) * PKin
PMax = 0.65 Pwn
[4] Double Drag Rotors cumulate both 'form drag' and 'induced lift drag'
coefficients for the airfoil facing the wind stream (which represents 2/3 of
the
area) and are reduced by 1/4 of the area submitted to a drag coefficient
opposite the wind stream:
PMax = PKin * (CDf + CDi) = {2/3 * 16/27 * (2.3 + 0.6) - 1 /4 * 16/27 * 1.2) *
PKin
PMax = 0.9 PKin
Because the deflectors, which are part of the airfoil of Drag Rotors, are not
exploited and part of the wind is therefore deflected outside the device
before
hitting the rotors, this phenomenon must be computed as reducing 10 - 15 %
the maximum power that may be collected, i.e. PMax = 0.8 PKin
b) Overall weight
[11] All of the equipment for converting wind power into a useful form is
installed on
the ground rather than on the top of the tower. This enables:
CA 02677016 2009-08-28
- the tower, which can comprise one third of the cost of a conventional wind
turbine, can be lighter because it need not hold the weight of heavy
equipment at the top, which in conventional wind turbines can exceed 50
tons.
- therefore, the entire frame can be built using hollowed bars in metal which
have only to be cut, rolled, welded and/or bolted together. Therefore a
Drag Rotor can be manufactured in a very short period of time. (see Figure
6a-6b-6c).
- the Drag Rotor may be equipped with sails, like boat sails, in light cloth
materials such as Kevlar, Mylar or Dacron (see Figure 7a-7b), using
battens to maintain the shape.
c) Infrastructure
[12] Installing Drag Rotors does not require any special infrastructure such
as
foundations, road constructions, telephone and cabling at the site or prior to
transportation to the site as required by conventional wind turbines.
[13] Also, Drag Rotors more easily meet environmental regulations than
conventional wind turbines and rotors.
d) Performance
[14] Using a Drag Rotor optimizes the torque exploited by the downstream
application and operates at much lower wind speeds than other rotors. By using
a Drag Rotor:
- the power collected from the wind per square meter of the Drag Rotor is
greater than that collected per square meter of a conventional wind rotor
- the rendering ratio for wind power collection is over 80% compared to less
than 30% with propellers of conventional wind turbine rotors
- the foil surface area of the Drag Rotor may be less than the rotor of a
conventional wind turbine to collect the same amount of wind energy.
6
CA 02677016 2009-08-28
the overall height of the Drag Rotor can be lower and thereby easier to
protect against storms.
- Drag Rotors can be lighter thereby enabling turning, initiating turning and
creating the requisite torque at slower wind speeds than conventional wind
rotors.
the Drag Rotor is less sensitive to potential turbulences due to surrounding
terrain and wind shear (e.g. agricultural land with some houses and
sheltering hedgerows with some 500 m intervals means that heights of only
meters above the ground are sufficient for a drag type collector,
whereas heights of greater than 80 meters generally are required for
conventional wind turbines).
- Drag Rotor produces less noise than conventional wind turbines and
rotors.
e) Dimensions versus torque
[15] With Drag Rotors, it is the creation of torque by the kinetic power of
the wind
that is important, to be exploited as a power source. Drag Rotors may be
dimensioned specially to fit better with the average wind speed where they are
installed: how slow are the regular winds, how wide the foil surface should be
versus limiting the height (while using the same foil surface). This can
increase
the torque sufficiently for reduced winds and enable the shaft to receive
enough
force for actuating the downstream device at slow levels.
f) Capacity Utilization
[16] The Drag Rotor can be sized so that the Process can achieve 100% power
production, and therefore capacity utilization, at a larger range of wind
speeds
whereas conventional wind turbine rotors are sized to achieve about 40% power
production, and therefore capacity utilization, at wind speeds of 12.5 m/s
(see
Figure 5f).
7
CA 02677016 2009-08-28
g) Costs
[17] Reducing significantly the costs for building, installing and maintaining
a wind
rotor, represents a major objective of the invention:
- There are no particular needs for Drag Rotors to be made out of expensive
special materials, like a matrix of GRP (Glass fiber reinforced polyester) as
used for conventional wind propellers, so manufacturing costs can be
significantly lower.
- The frame can be entirely made of hollowed bars in metal.
- Their design makes it easy to specifically size a wide range of power
collection thereby meeting the needs of the individual customer
- Drag Rotors also are less expensive and easier to build, to fix and to
maintain:
^ All of the equipment for collecting wind power is installed on the ground
rather than on the top of the tower, so the tower can be lighter and cost
a lot less.
^ Manufacture, installation and operation requires less skilled labor than
conventional wind turbines
^ Assembly can be made without heavy equipment and cranes which are
very expensive, therefore making Drag Rotors easier to install almost
everywhere
^ This also can reduce the time from manufacture to installation (e.g. 90
to 180 days compared to more than up to 2 years for conventional wind
power)
^ Maintenance costs, including refurbishment and major overhauls, are
reduced, because of the ease of accessing the equipment and lack of
sensitive equipment comprising a conventional wind turbine
8
CA 02677016 2009-08-28
^ Production costs are reduced because performance (see above) is
improved.
[18] Other systems, methods, features and advantages of the invention will be,
or
will become, apparent to one with skill in the art upon examination of the
following figures and detailed description. It is intended that all such
additional
systems, methods, features and advantages be included within the description,
be within the scope of the invention, and be protected by the claims above.
Areas of Application
[19] While the invention intends first to use Drag Rotors in the Process to
run a
generator better to produce electricity, it is designed more generally as a
Wind
Collector where the kinetic force of the wind, being converted as torque, can
actuate any engine that requires such torque rather than velocity. This means
that Drag Rotors may replace other types of Wind Turbines or Wind Mills for a
number of uses, including:
o reverse osmosis
o sewage
o draining or pumping
o energy storage using elevated containers
o powering tools and/or industrial facilities
o production of electricity.
Embodiments of the Invention
[20] A Drag Rotor may have either a horizontal or vertical shaft, however a
frame
based on a Vertical Double Drag model (coupling two vertical axis rotors) is
more particularly described hereunder. (see Figure 1)
[21] The preferred embodiment of a Drag Rotor is to use sails shaped like an
arc of
9
CA 02677016 2009-08-28
cylinder or using a spiral spine, with an off-centered axis of the central
rotor
versus the external circle. One side of the sail is guided alongside the
external
circle (the Stator) while the other side swivels while turning with the
central rotor
wheel. (see Figure 5b) This "off-centered" motion enables each sail to turn
separately and differently from the others according to its position with the
rotor's shaft.
1. The Rotor
[22] According to the innovation of the Process, the invention proposes
specially
designed "Double Drag Rotors" whose sails are made of lighter and different
materials (e.g. Dacron, Kevlar or Mylar) and which optimize the torque
exploited
by the Process and operate at much lower wind speeds than other rotors. The
design improves performance by exploiting torque rather than velocity, while
based on drag factors rather than lift effects:
a) Torque versus Speed
o In the Process, it is the creation of torque by the kinetic power that is
important rather than the rotary speed transferred from the Rotor to the
downstream engine shaft. Conversely, with conventional horizontal Wind
Turbines (or Darrieus turbines), the velocity that the wind may give to the
propellers is more important.
o Conceptually, any design and type of Rotor may be used as long as it
produces a torque to turn a shaft connected to the Rotor, so that the shaft
actuates the downstream application (e.g. high torque with slow rotational
speed rather than smaller torque with high rotary motion, as with Savonius
Rotors)
b) Drag versus Lift
o In aerodynamics, the "Lift" force is defined to be the component of the
force exerted on a body by a fluid flowing past its surface, which is
perpendicular to the oncoming flow direction.
CA 02677016 2009-08-28
With conventional Wind Rotors, made of propellers, the blades' airfoil is a
streamlined shape that is capable of generating significantly more lift than
drag.
o It contrasts with "Drag" (sometimes called air resistance or fluid
resistance)
which refers to forces that oppose the relative motion of an object through
a fluid (a liquid or gas, including air). Drag forces act in a direction
opposite
to the oncoming flow velocity. Unlike other resistive forces such as dry
friction, which is nearly independent of velocity, drag forces depend only on
wind velocity.
In aerodynamics, two types of drag must be considered for Wind Rotors:
= "lift-induced drag", which is a drag force that occurs whenever a moving
object redirects the airflow coming at it (see Figure 1 a)
= "form drag", which arises because of the form of the object (see Figure
4).
c) Closed versus open frame
[23] The Rotor frame generally is made of a tube. This enables capturing
better the
wind in the vanes that are formed with the sails, the space between two sails
shaping a kind of a paddle. However such model requires the sails to be
designed specially (as a spiral spine) to ensure they do not contact the tube
or
the other sails. (see Figure 5b)
[24) Otherwise, the Rotor frame may be made of two wheels (fixed at the top
and the
bottom of the sails). In this model, the shape of the sails generally is
simplified
as a simple arc of cylinder (see Figure 5a). However, here the sails do not
create a closed space working like a paddle. Instead, the wind hitting the
sails is
redirected to the center of the Rotor and then hits the other sails, creating
a
"Savonius" effect. The advantages of either solution will be apparent to one
with
skill in the art upon examination of the requirements resulting from the wind
conditions where the Drag Rotors should be installed.
11
CA 02677016 2009-08-28
2. The Sails
a) Swiveling / sliding sails
[25] Drag Rotors use "swiveling / sliding rotary curved sails" instead of
blades, and
therefore work more like boat-sails or Savonius scoops than the wings or blade
propellers of the conventional wind industry, which are based principally on
the
lift effect.
o Drag Rotors are 'Drag Devices' because both types of drag are exploited
when the wind hits the sails while passing through the two rotors (i.e. form
drag and induced lift drag) to convert as torque a maximum of the collected
energy which results from the volume and speed of the wind stream. (See
Figure 5a)
o The frame and positioning of the sails are designed to optimize exploitation
of these drag phenomena, which include but are not limited to:
= Coupling two rotors, assembled together in opposite direction for limiting
negative drag impediments (See Figure 5c)
= Using so-called "double drag" sails (arc of cylinder or spiral spine)
because
their shape enables both `form drag' and `induced lift drag' to better
increase the quantity of energy collected from the wind stream velocity
(See Figure 5a)
= Off-centering the axle of the rotors to enable the angle of the sails versus
the wind stream to vary while the rotor turns (See Figure 5d), enhancing
the sail efficiency to the drag when positioned to work as positive drag sail
on the windward side and reversely reducing the drag effect, on the
leeward side and therefore
= The sails are sliding and guided alongside the stator while they turn around
the rotor axle where they are swiveling, so that they offer as much as
possible a better induced downwash angle and may work better regardless
of their position,
12
CA 02677016 2009-08-28
= Because of the angle formed by the sail versus the Rotor, the push force of
the wind becomes effective only when the sail retrieves its position of
"positive drag sail" and transmits the power collected from the wind to the
Rotor. (see Figure 5c)
b) Minimizing negative drag
[26] Using deflectors enables protecting the sails from being submitted to
negative
drag, so that any negative drag is minimized almost to become insignificant.
Because of the deflectors, the wind pushes on the sails only on the external
half
side of the rotor and there is about no effect of the wind on the sails while
turning around the Rotor to come back to the front (where sails could be
called
"negative drag sails").
c) Automatic variable displacement
[27] Also, because sails are not rigid but use material made of cloth like
boat sails
(including for example, Nylon, Mylar, Kevlar, Dacron or similar materials), it
enables the installation of mechanisms for reducing automatically the sails
surface in case of storms or very high winds. This not only enables protecting
the device from eventual damage, but facilitates the adaptation of the volume
of
power collected to the needs of the downstream equipment.
[28] This is possible either by adding any mechanism which enables dropping
the
sails or integrating rollers in the sails' frame (e.g. on the rotor's side).
The
system of rolling furlers should be preferred as it enables automatically to
regulate the foil surface of the sail by comparison with the rotational speed
of
the rotor, while using springs on the stator side for keeping the sail open as
much as needed. (see Figure 7a)
[29) Doing so, the Drag Rotor becomes a "variable turbine" which enables
controlling
easier the volumes of water flow handled downstream without use of a gearbox
and other regulatory mechanisms, which generally result in major losses of
energy inefficiencies.
13
CA 02677016 2009-08-28
3. The Frame
a) Improving Wind Power Collection
[30] Efficiency is improved when the drag differential of opposing sails of a
rotor is
the greatest possible. Therefore, different principles were applied when
designing the Drag Rotor, with swiveling / sliding sails and deflectors:
= Reducing the negative drag applicable to less than 1/8 of each rotor
o by using deflectors to redirect part of the wind to the working airfoils
o by reducing the airfoil and angle of the sails whose position would
submit them to negative drag
= Increasing the airfoil submitted to the "form drag" (i.e. the drag which
arises
because of the form of the object - CDf)
o by grouping a maximum of working sails in the stream of the wind - CD
o by orientating the sails so that they are the most perpendicular to the
wind direction
= Developing the "induced lift drag" factor (i.e. drag force that occurs when
an object redirects the airflow coming at it - Co; - See Figure 5e)
o by organizing a depression area at the rear of the Drag Rotor where
o the stream of air passing through the device, and so being slowed
down, is submitted to a suction phenomenon (= induced lift drag) due to
the suction generated by the wind deflected around the device.
= Using torque as great as possible (see Figures 5 & 6b)
o by using a design where dimensions of the frame are calculated to offer
the best Rotor's diameter versus the height with the required foil
surface. Also, making the frame wider than taller means that the Rotor
will turn slower and may work with larger range of wind speed.
o A slower rotation with a more important torque improves the possible
transfer of energy to the Hydraulic Generator actuated by the Rotor
(see Hydraulic Generator Patent), especially when normal wind speed
average to exploit is low.
14
CA 02677016 2009-08-28
b) Coupling two rotors in the same frame
[31] Using two opposite rotors in a common frame (see Figures 6a & 6b) enables
improving significantly the reduction of negative drags. The pair of
deflectors
may work by redirecting on both directions all the wind which would affect
"negative drag sails". This enables each rotor to capture one half of the
overall
foil surface (see Figure 5c), including the deflectors area.
c) Automatically orientating itself
[32] The frame is mounted on three masts, thereby forming a tripod (see Figure
6c):
^ The main mast in front is dedicated to support the weight of the structure
and
to bring resistance to the frame for standing up. Also, as it may rotate, it
enables the entire frame to turn around.
^ The two other supports are made of the shafts ("secondary masts") of the
Drag Rotors and each is mounted on a wheel. Because the Rotors offer a
resistance to the wind push, these secondary masts automatically roll behind
the main mast to place themselves "under the wind".
Conclusions
[33] Primarily, the invention intends to improve collection of medium range
wind
energy of 10 kilo Watts (kW) to 1 mega Watt (mW), by proposing a genuine
design of a wind rotor (the "Drag Rotor") based on the usage of Drag forces.
[34] For improving maximum efficiency the Drag Rotor is
o exploiting
= drag forces rather than lift effect
= torque rather than velocity
o replacing
= thrust on spinning angular blades of a propeller by thrust on
perpendicular foil of sails
= tall heavy structure by lower extra light frame
CA 02677016 2009-08-28
o coupling two rotors within the same frame:
= means that the deflectors are protecting sails from negative drag.
= enables the Double Drag Rotors to exploit 100% of the foil surface.
o automatically oriented to work "under the wind".
o enabling to function as a "variable displacement" device by varying the foil
surface of the sails according to the needs, but also therefore reducing
significantly the risks of damage with storm conditions.
[35] Drag rotors enables 100% of production efficiency within a range of wind
speed
of 2-3 meters/second up to 22 meters/second, which represents 80% of the
energy contained in the wind, whereas conventional wind turbines can only
produce 40% at 12.5 meters/second with a valuable production efficiency
limited
from 8 m/s to 14 m/s.
[36] Reducing the costs for building, installing and maintaining of a wind
collector
represents another major objective of the Drag Rotor invention.
[37] The present invention has been described with regard to one or more
embodiments. However, it will be apparent to persons skilled in the art that a
number of variations and modifications can be made without departing from the
scope of the invention as defined in the claims. All citations are hereby
incorporated by reference.
16
