US 20090087308 A2
A Mixer/Ejector Wind Turbine (“MEWT”) system is disclosed which routinely exceeds the efficiencies of prior wind turbines. In the preferred embodiment, Applicants' MEWT incorporates advanced flow mixing technology, single and multi-stage ejector technology, aircraft and propulsion aerodynamics and noise abatement technologies in a unique manner to fluid-dynamically improve the operational effectiveness and efficiency of wind turbines, so that its operating efficiency routinely exceeds the Betz limit. Applicants' preferred MEWT embodiment comprises: an aerodynamically contoured turbine shroud with an inlet; a ring of stator vanes; a ring of rotating blades (i.e., an impeller) in line with the stator vanes; and a mixer/ejector pump to increase the flow volume through the turbine while rapidly mixing the low energy turbine exit flow with high energy bypass wind flow. The MEWT can produce three or more time the power of its un-shrouded counterparts for the same frontal area, and can increase the productivity of wind farms by a factor of two or more. The same MEWT is safer and quieter providing improved wind turbine options for populated areas.
1. In an axial flow wind turbine of the type having an aerodynamically contoured turbine shroud with an inlet and an impeller downstream having a ring of impeller blades, the improvement comprising:
a. a ring of stator vanes upstream of the impeller;
b. a ring of mixer lobes, wherein the mixer lobes extend downstream of the impeller blades; and
c. an ejector shroud surrounding the ring of mixer lobes, wherein the mixer lobes extend downstream and into the ejector shroud.
2. The wind turbine of
3. The wind turbine of
4. The wind turbine of
5. The wind turbine of
6. The wind turbine of
7. The wind turbine of
8. An axial flow wind turbine comprising:
a. an aerodynamically contoured turbine shroud with an inlet;
b. a ring of stator vanes mounted within the turbine shroud, of the axial flow wind turbine, wherein the stator vanes have leading edges and trailing edges;
c. a ring of impeller blades rotatably mounted within the turbine shroud, of the axial flow wind turbine, wherein the impeller blades have leading edges adjacent trailing edges of respective stator vanes; and
d. means for consistently exceeding the Betz limit for operational efficiency of the axial flow wind turbine, wherein the means comprises:
(i) a ring of mixer lobes wherein the lobes extend downstream of the impeller blades; and
(ii) an ejector shroud surrounding the ring of mixer lobes, wherein the mixer lobes extend downstream and into the ejector shroud.
9. An axial flow wind turbine comprising:
a. an aerodynamically contoured turbine shroud with an inlet;
b. a turbine stage, mounted within the shroud, comprising:
(i) a ring of stator vanes, downstream of the inlet, mounted on a support shaft attached to the turbine shroud;
(ii) a ring of impeller blades, downstream of the stator vanes, mounted on the support shaft;
c. a ring of mixer lobes wherein the lobes extend downstream of the impeller blades; and
d. an ejector surrounding trailing edges of the mixer lobes and extending downstream from the mixer lobes.
10. In an axial flow wind turbine of the type having an aerodynamically contoured turbine shroud with an inlet and an impeller downstream having a ring of impeller blades, the improvement comprising: a stator ring, upstream of the impeller, having stator vanes; and a mixer, attached to the shroud, having a ring of mixer lobes extending downstream of the impeller blades; and an ejector extending downstream from the ring of mixer lobes.
11. In an axial flow wind turbine of the type having a shroud with an inlet and a propeller-like rotor, the improvement comprising a mixer having a ring of mixer lobes extending downstream of the impeller blades.
12. The axial flow wind turbine of
This application claims priority from Applicants' U.S. Provisional Patent Application Ser. No. 60/919,588, filed Mar. 23, 2007 (hereinafter “Applicants' Provisional Application”). Applicants hereby incorporate the disclosure of Applicants' Provisional Application by reference.
The present invention deals generally with axial flow turbines. More particularly, it deals with axial flow wind turbines.
Wind turbines usually contain a propeller-like device, termed the “rotor”, which is faced into a moving air stream. As the air hits the rotor, the air produces a force on the rotor in such a manner as to cause the rotor to rotate about its center. The rotor is connected to either an electricity generator or mechanical device through linkages such as gears, belts, chains or other means. Such turbines are used for generating electricity and powering batteries. They are also used to drive rotating pumps and/or moving machine parts. It is very common to find wind turbines in large electricity generating “wind farms” containing multiple such turbines in a geometric pattern designed to allow maximum power extraction with minimal impact of each such turbine on one another and/or the surrounding environment.
The ability of a rotor to convert fluid power to rotating power, when placed in a stream of very large width compared to its diameter, is limited by the well documented theoretical value of 59.3% of the oncoming stream's power, known as the “Betz” limit as documented by A. Betz in 1926. This productivity limit applies especially to the traditional multi-bladed axial wind/water turbine presented in
Attempts have been made to try to increase wind turbine performance potential beyond the “Betz” limit. Shrouds or ducts surrounding the rotor have been used. See, e.g., U.S. Pat. No. 7,218,011 to Hiel et al. (see
Values two times the Betz limit allegedly have been recorded but not sustained. See Igar, O., Shrouds for Aerogenerators, AIAA Journal, October 1976, pp. 1481-83; Igar & Ozer, Research and Development for Shrouded Wind Turbines, Energy Cons. & Management, Vol. 21, pp. 13-48, 1981; and see the AIAA Technical Note, entitled “Ducted Wind/Water Turbines and Propellers Revisited”, authored by Applicants (“Applicants' AIAA Technical Note”), and accepted for publication. Copies can be found in Applicants' Information Disclosure Statement. Such claims however have not been sustained in practice and existing test results have not confirmed the feasibility of such gains in real wind turbine application.
To achieve such increased power and efficiency, it is necessary to closely coordinate the aerodynamic designs of the shroud and rotor with the sometimes highly variable incoming fluid stream velocity levels. Such aerodynamic design considerations also play a significant role on the subsequent impact of flow turbines on their surroundings, and the productivity level of wind farm designs.
Ejectors are well known and documented fluid jet pumps that draw flow into a system and thereby increase the flow rate through that system. Mixer/ejectors are short compact versions of such jet pumps that are relatively insensitive to incoming flow conditions and have been used extensively in high speed jet propulsion applications involving flow velocities near or above the speed of sound. See, for example, U.S. Pat. No. 5,761,900 by Dr. Walter M. Presz, Jr, which also uses a mixer downstream to increase thrust while reducing noise from the discharge. Dr. Presz is a co-inventor in the present application.
Gas turbine technology has yet to be applied successfully to axial flow wind turbines. There are multiple reasons for this shortcoming. Existing wind turbines use non-shrouded turbine blades to extract the wind energy. As a result, a significant amount of the flow approaching the wind turbine blades flows around and not through the blades. Also, the air velocity decreases significantly as it approaches existing wind turbines. Both of these effects result in low flow through, turbine velocities. These low velocities minimize the potential benefits of gas turbine technology such as stator/rotor concepts. Previous shrouded wind turbine approaches have keyed on exit diffusers to increase turbine blade velocities. Diffusers require long lengths for good performance, and tend to be very sensitive to oncoming flow variations. Such long, flow sensitive diffusers are not practical in wind turbine installations. Short diffusers stall, and just do not work in real applications. Also, the downstream diffusion needed may not be possible with the turbine energy extraction desired at the accelerated velocities. These effects have doomed all previous attempts at more efficient wind turbines using gas turbine technology.
Accordingly, it is a primary object of the present invention to provide an axial flow wind turbine that employs advanced fluid dynamic mixer/ejector pump principles to consistently deliver levels of power well above the Betz limit.
It is another primary object to provide an improved axial flow wind turbine that employs unique flow mixing (for wind turbines) and control devices to increase productivity of and minimize the impact of its attendant flow field on the surrounding environment located in its near vicinity, such as found in wind farms.
It is another primary object to provide an improved axial flow wind turbine that pumps in more flow through the rotor and then rapidly mixes the low energy turbine exit flow with high energy bypass wind flow before exiting the system.
It is a more specific object, commensurate with the above-listed objects, which is relatively quiet and safer to use in populated areas.
A mixer/ejector wind turbine system (nicknamed the “MEWT”) for generating power is disclosed that combines fluid dynamic ejector concepts, advanced flow mixing and control devices, and an adjustable power turbine.
In the preferred embodiment, the MEWT is an axial flow turbine comprising, in order going downstream: an aerodynamically contoured turbine shroud having an inlet; a ring of stators within the shroud; an impeller having a ring of impeller blades “in line” with the stators; a mixer, attached to the turbine shroud, having a ring of mixing lobes extending downstream beyond the impeller blades; and an ejector comprising the ring of mixing lobes (e.g., like that shown in U.S. Pat. No. 5,761,900) and a mixing shroud extending downstream beyond the mixing lobes. The turbine shroud, mixer and ejector are designed and arranged to draw the maximum amount of fluid through the turbine and to minimize impact to the environment (e.g., noise) and other power turbines in its wake (e.g., structural or productivity losses). Unlike the prior art, the preferred MEWT contains a shroud with advanced flow mixing and control devices such as lobed or slotted mixers and/or one or more ejector pumps. The mixer/ejector pump presented is much different than used in the aircraft industry since the high energy air flows into the ejector inlets, and outwardly surrounds, pumps and mixes with the low energy air exiting the turbine shroud.
In this first preferred embodiment, the MEWT comprises: an axial flow wind turbine surrounded by an aerodynamically contoured turbine shroud incorporating mixing devices in its terminus region (i.e., an end portion of the turbine shroud) and a separate ejector duct overlapping but aft of said turbine shroud, which itself may incorporate advanced mixing devices in its terminus region.
In an alternate embodiment, the MEWT comprises: an axial flow wind turbine surrounded by an aerodynamically contoured turbine shroud incorporating mixing devices in its terminus region.
First-principles-based theoretical analysis of the preferred MEWT indicates that the MEWT can produce three or more time the power of its un-shrouded counterparts for the same frontal area, and increase the productivity of wind farms by a factor of two or more.
Applicants believe, based upon their theoretical analysis, that the preferred MEWT embodiment will generate three times the existing power of the same size conventional wind turbine.
Other objects and advantages of the current invention will become more readily apparent when the following written description is read in conjunction with the accompanying drawings.
Referring to the drawings in detail,
In the preferred embodiment (see
The center body 103 MEWT 100, as shown in
Applicants have calculated, for optimum efficiency in the preferred embodiment 100, the area ratio of the ejector pump 122, as defined by the ejector shroud 128 exit area over the turbine shroud 102 exit area will be between 1.5 and 3.0. The number of mixer lobes (e.g., 120 a) would be between 6 and 14. Each lobe will have inner and outer trailing edge angles between 5 and 25 degrees. The primary lobe exit location will be at, or near, the entrance location or inlet 129 of the ejector shroud 128. The height-to-width ratio of the lobe channels will be between 0.5 and 4.5. The mixer penetration will be between 50% and 80%. The center body 103 plug trailing edge angles will be thirty degrees or less. The length to diameter (L/D) of the overall MEWT 100 will be between 0.5 and 1.25.
First-principles-based theoretical analysis of the preferred MEWT 100, performed by Applicants, indicate: the MEWT can produce three or more time the power of its un-shrouded counterparts for the same frontal area; and the MEWT can increase the productivity of wind farms by a factor of two or more. See Applicants' AIAA Technical Note, identified in the Background above, for the methodology and formulae used in their theoretical analysis.
Based on their theoretical analysis, Applicants believe their preferred MEWT embodiment 100 will generate three times the existing power of the same size conventional wind turbine (shown in
In simplistic terms, the preferred embodiment 100 of the MEWT comprises: an axial flow turbine (e.g., stator vanes and impeller blades) surrounded by an aerodynamically contoured turbine shroud 102 incorporating mixing devices in its terminus region (i.e., end portion); and a separate ejector shroud (e.g., 128) overlapping, but aft, of turbine shroud 102, which itself may incorporate advanced mixing devices (e.g., mixer lobes) in its terminus region. Applicants' ring 118 of mixer lobes (e.g., 120 a) combined with the ejector shroud 128 can be thought of as a mixer/ejector pump. This mixer/ejector pump provides the means for consistently exceeding the Betz limit for operational efficiency of the wind turbine.
Applicants have also presented supplemental information for the preferred embodiment 100 of MEWT shown in
The length of the turbine shroud 102 is equal or less than the turbine shroud's outer maximum diameter. The length of the ejector shroud 128 is equal or less than the ejector shroud's outer maximum diameter. The exterior surface of the center body 103 is aerodynamically contoured to minimize the effects of flow separation downstream of the MEWT 100. It may be longer or shorter than the turbine shroud 102 or the ejector shroud 128, or their combined lengths.
The turbine shroud's entrance area and exit area will be equal to or greater than that of the annulus occupied by the turbine stage 104, but need not be circular in shape so as to allow better control of the flow source and impact of its wake. The internal flow path cross-sectional area formed by the annulus between the center body 103 and the interior surface of the turbine shroud 102 is aerodynamically shaped to have a minimum area at the plane of the turbine and to otherwise vary smoothly from their respective entrance planes to their exit planes. The turbine and ejector shrouds' external surfaces are aerodynamically shaped to assist guiding the flow into the turbine shroud inlet, eliminating flow separation from their surfaces, and delivering smooth flow into the ejector entrance 129. The ejector 128 entrance area, which may be noncircular in shape (see, e.g.,
Optional features of the preferred embodiment 100 can include: a power take-off 130 (see
MEWT 100, when used near residences can have sound absorbing material 138 affixed to the inner surface of its shrouds 102, 128 (see
Note that Applicants' alternate MEWT embodiments, shown in
Applicants' alternate MEWT embodiments are variations 200, 300, 400, 500 containing zero (see, e.g.,
It should be understood by those skilled in the art that obvious structural modifications can be made without departing from the spirit or scope of the invention. For example, slots could be used instead of the mixer lobes or the ejector lobes. In addition, no blocker arm is needed to meet or exceed the Betz limit. Accordingly, reference should be made primarily to the appended claims rather than the foregoing description.