CA2677016A1

CA2677016A1 - Double drag wind rotor

Info

Publication number: CA2677016A1
Application number: CA2677016A
Authority: CA
Inventors: Jean Pierre Hofman; Bruce I. Benn
Original assignee: Individual
Current assignee: Individual
Priority date: 2009-08-28
Filing date: 2009-08-28
Publication date: 2011-02-28
Also published as: WO2011022836A8; WO2011022836A1

Abstract

The invention describes a Wind Collector, referred to as the Drag Rotor, based on the air resistance, called the Drag, which is engendered by the foil surface of its body. In the wind industry, Rotors function as transformers of wind power into rotational motion, where stabilized velocity is primarily significant. In the Wind-Hydro Generator Process, referred to as the Process, and developed in a separate patent application, this rotation of the Drag Rotors transmits a torque, which turns a shaft, which actuates a Hydraulic Generator (pump, or motor or turbine acting like a pump), and converts the wind energy into kinetic force of a water flow (See Figure 6d). Drag Rotors preferably are coupled (see Figure 1) to enhance the wind power collection by using a common central deflector which enables minimizing any potential "negative drag". However a Drag Rotor may be exploited in single structure, using either a vertical or horizontal axis and according to the location where it is to be installed (e.g.
on the roof of a building where a horizontal positioning would be more user friendly or conform to local regulations - see Figure la). Drag Rotors use sails shaped like an arc of a cylinder or using a spiral spine, with an off-centered axis of the central rotor versus the stator. 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. This "off-centered" motion enables each sail to turn separately and differently from the others according to its position with the rotor's shaft. The sails being made of cloth enables varying the dimensions of the overall foil surface of the Drag Rotor simply by modifying the height or the width of the sails, like on sail boats, so that they offer only resistance to the wind as the user needs, (e.g. in storm conditions where it may be dropped entirely). Unlike conventional wind turbines, Drag Rotors may be considered as variable displacement devices.

Description

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

[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:

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 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

[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 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.

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 [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:

- 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.

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).

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 ^ 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 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.

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.

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, = 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.

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.

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 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.

Claims

1. A Wind Turbine comprising Sails in a Drag Rotor configuration to capture low velocity, high torque wind energy;

said Drag Rotor Configuration being designed to enhance exploitation of both Form Drag and Lift Drag.

2. The Turbine of claim 1 wherein said Sails are fixed on axles attached to a tube of the Rotor, said tube rotating about an axis of the shaft of the Rotor, said axis being off-centre with the central axis of the Stator of said Turbine.

3. The Turbine of either one of claims 1 or 2 wherein said Sails swivel around said axles.

4. The Turbine of any one of claims 1 to 3 wherein said Sails are guided to slide alongside the Stator.

5. The Turbine of any one of claims 1 to 4 wherein said Sails, swiveling against the Rotor's tube, form Vanes providing a variable displacement configuration.

6. The Turbine of any one of claims 1 to 5 comprising two Rotors within the same Frame.

7. The Turbine of any one of claims 1 to 6 wherein said Vanes create an inside form drag phenomenon when opposed to the wind flow while said Sails are shaped to create a lift drag phenomenon on their extrados.

8. The Turbine of any one of claims 1 to 7 assembled within a Frame which is designed to turn on itself and to enable automatic orientation of said Frame perpendicularly to Wind direction.

9. The Turbine of any one of claims 1 to 8 comprising deflectors fixed on the front side of the Frame to shield Sails from negative drag.

10. The Turbine of any one of claims 1 to 9 wherein said Sails are in a variable displacement arrangement, varying the foil surface of the Sails according to the needs.

11. The Turbine of any one of claims 1 to 10 wherein the components of said Turbine are configured to capture medium-range energy.

12. The Turbine of any one of claims 1 to 11 comprising deflectors to block wind from said Sails while rotating said Sails back into a wind-capturing position.

13. The Turbine of any one of claims 1 to 12 wherein said Sails are arcuate in cross-section.

14. The Turbine of any one of claims 1 to 13 wherein said Sails further comprise stiffening battens.