WO2011140411A1

WO2011140411A1 - Fluid turbine with ejector shroud

Info

Publication number: WO2011140411A1
Application number: PCT/US2011/035459
Authority: WO
Inventors: Jr. Walter M. Presz; Michael J. Werle
Original assignee: Flodesign Wind Turbine Corp.
Priority date: 2010-05-07
Filing date: 2011-05-06
Publication date: 2011-11-10
Also published as: US20110135460A1

Abstract

A fluid turbine includes a turbine shroud and an ejector shroud. The turbine shroud has an axial length L_M. The ejector shroud has an axial length L_E. The ratio of L_M to L_E may be from 0.05 to 2.5. In particular embodiments, the ejector shroud has an axial length L_E, an outer diameter D_I at the inlet end, and an outer diameter D_E at the exhaust end. The ratio of L_E to D_I may be from 0.05 to 3; and the ratio of L_E to D_E may be from 0.05 to 3. The resulting ejector shroud may be 30% - 50% shorter than ejector shrouds of previous designs.

Description

FLUID TURBINE WITH EJECTOR SHROUD

BACKGROUND

[0001] The present disclosure relates to a shrouded fluid turbine having a turbine shroud and an ejector shroud downstream of the turbine shroud and optionally surrounding the rear end of the turbine shroud. It has been discovered that a shorter ejector shroud achieves higher efficiency and lower weight compared to previous shrouded wind turbines. The fluid turbines may be used to extract energy from fluids such as air (i.e. wind) or water. The aerodynamic principles of a mixer ejector wind turbine also apply to hydrodynamic principles of a mixer ejector water turbine.

[0002] Conventional horizontal axis wind turbines (HAWTs) used for power generation have two to five open blades arranged like a propeller, the blades being mounted to a horizontal shaft that is engaged with a power generator. HAWTs will not exceed 59.3% efficiency in capturing the potential energy of the wind in the blades swept area.

BRIEF DESCRIPTION

[0003] The present disclosure relates to shrouded fluid turbines including a turbine shroud and an ejector shroud. The turbine shroud has mixing lobes along a trailing edge of the turbine shroud. The turbine shroud has an axial length LM, the ejector shroud has an axial length LE, and the ratio of LM to LE is greater than in prior shrouded wind turbines.

[0004] Disclosed in some embodiments is a fluid turbine including a turbine shroud and an ejector shroud. The turbine shroud has a front end and a rear end. The ejector shroud has an inlet end and an exhaust end. The rear end of the turbine shroud has a plurality of mixing lobes along a trailing edge. Sometimes, the mixing lobes extend into the inlet end of the ejector shroud. The turbine shroud has an axial length LM. The ejector shroud has an axial length LE. The ratio of LM to LE is from

0.05 to 2.5 (0.05 < ^ < 2.5).

[0005] In more specific embodiments, the ratio of LM to LE is from 0.16 to 2.1 (0.16 < ^ < 2.1).

[0006] The ejector shroud has an outer diameter Di at the inlet end, and the ratio of L_E to Di may be from 0.05 to 3.0 (0.05 < ¾ < 3.0). The ejector shroud has an outer diameter D_E at the exhaust end, and the ratio of L_E to DE may be from 0.05 to 3.0 (0.05 <— < 3.0).

[0007] The turbine shroud has an outer diameter DF at the front end, and the ratio of LM to D_F may be from 0.1 to 2.5 (0.1 <— < 2.5). The turbine shroud has an outer

Op

diameter DRO at the rear end, and the ratio of L_M to D O may be from 0.1 to 1.25 (0.1 <— < 1.25). The turbine shroud has an inner diameter DRI at the rear end, and

DRO

the ratio of L_M to D I may be from 0.1 to 3.5 (0.1 <— < 3.5). The ratio of D_RO to DRI

DR/

may be from 0.7 to 2 (0.7 < ^ < 2).

^DRi

[0008] The wind turbine has a total axial length L_T) and the ratio of L_M to L_T may be from 0.05 to 1.0, including from 0.1 to 0.9 ( 0.1 < ^ < 0.9). The ratio of L_E to L_T may be from 0.05 to 0.9 (0.05 <— < 0.9).

[0009] In some desired embodiments, the ejector shroud has a ring airfoil shape and does not have mixing lobes. In other embodiments, the ejector shroud has mixing lobes.

[0010] In embodiments, the plurality of mixing lobes on the turbine shroud includes a set of high energy mixing lobes and a set of low energy mixing lobes, the high energy mixing lobes having an angle of about 10° to about 50° relative to a horizontal axis that is parallel to the central axis of the turbine shroud.

[0011 ] The fluid turbine may further include a nacelle body located within the turbine shroud. The nacelle body, turbine shroud, and ejector shroud are coaxial to each other. In some embodiments, the nacelle body includes a central passageway.

[0012] Also disclosed is a fluid turbine having a turbine shroud and an ejector shroud. The turbine shroud has a front end and a rear end. The ejector shroud has an inlet end and an exhaust end. The rear end of the turbine shroud has a plurality of mixing lobes along a trailing edge. The mixing lobes can extend into the inlet end of the ejector shroud. The turbine shroud has an axial length L . The ejector shroud has an axial length L_E, an outer diameter D| at the inlet end, and an outer diameter DE at the exhaust end. The ratio of L_M to L_E is from 0.05 to 2.5; the ratio of LE to D₍ is from 0.05 to 3; and the ratio of L_E to D_E is from 0.05 to 3 (0.05 <— < 2.5 ; 0.05 < ½ < 3 ; 0.05 3).

Di D_E ' [0013] These and other non-limiting features or characteristics of the present disclosure will be further described below.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The following is a brief description of the drawings, which are presented for the purposes of illustrating the disclosure set forth herein and not for the purposes of limiting the same.

[0015] FIG. 1 is a cross-sectional view of a first example embodiment of a shrouded fluid turbine of the present disclosure, marked with reference numerals.

[0016] FIG. 2 is a cross-sectional view of the shrouded fluid turbine of FIG. 1 , showing various lengths of the fluid turbine.

[0017] FIG. 3 is a front left perspective view of the shrouded fluid turbine of FIG. 1.

[0018] FIG. 4 is a rear right perspective view of the shrouded fluid turbine of FIG. 1.

[0019] FIG. 5 is a front left perspective view of the shrouded fluid turbine of FIG. 1 with the rotor and nacelle removed, so that other aspects of the fluid turbine can be more clearly seen and explained.

[0020] FIG. 6 is a rear perspective cut-away view of the shrouded fluid turbine of FIG. 1. The rotor and nacelle are removed so that other aspects of the wind turbine can be more clearly seen and explained. The cross-sectional area at the rotor of the turbine shroud is illustrated here.

[0021] FIG. 7 is a rear perspective cut-away view of the shrouded fluid turbine of FIG. 1 , showing the exit area of the turbine shroud. The rotor and nacelle are not seen here.

[0022] FIG. 8 is a rear perspective cut-away view of the shrouded fluid turbine of FIG. 1 , showing the exit area of the ejector shroud. The rotor and nacelle are not seen here.

[0023] FIG. 9 is a rear view of the shrouded wind turbine of FIG. 1. The rotor and nacelle are removed from this figure so that other aspects of the wind turbine can be more clearly seen and explained.

[0024] FIG. 10 is a smaller view of the fluid turbine of FIG. 1.

[0025] FIG. 11 and FIG. 12 are magnified views of the mixing lobes of the wind turbine of FIG. 10. [0026] FIG. 13 is a cross-sectional view of a second example embodiment of a shrouded wind turbine of the present disclosure.

[0027] FIG. 14 is a cross-sectional view of the shrouded fluid turbine of FIG. 13, showing various lengths of the fluid turbine.

[0028] FIG. 15 is a cross-sectional view comparing the first example embodiment of FIG. 1 with the second example embodiment of FIG. 13.

[0029] FIG. 16 is a chart showing the power output (kilowatts) versus the wind velocity (mph), comparing a wind turbine with a shorter ejector shroud (i.e. the turbine of FIG. 13) to a wind turbine having a longer ejector shroud (i.e. the turbine of FIG. 1 ).

DETAILED DESCRIPTION

[0030] A more complete understanding of the components, processes, and apparatuses disclosed herein can be obtained by reference to the accompanying figures. These figures are intended to demonstrate the present disclosure and are not intended to show relative sizes and dimensions or to limit the scope of the present disclosure.

[0031] Although specific terms are used in the following description, these terms are intended to refer to particular structures in the drawings and are not intended to limit the scope of the present disclosure. It is to be understood that like numeric designations refer to components of like function.

[0032] The term "about" when used with a quantity includes the stated value and also has the meaning dictated by the context. For example, it includes at least the degree of error associated with the measurement of the particular quantity. When used in the context of a range, the term "about" should also be considered as disclosing the range defined by the absolute values of the two endpoints. For example, the range "from about 2 to about 4" also discloses the range "from 2 to 4."

[0033] A Mixer-Ejector Fluid/Water Turbine (MEWT) provides an improved means of generating power from fluid currents. A primary shroud contains an impeller which extracts power from a primary fluid stream. A mixer-ejector pump may be included that ingests flow from the primary fluid stream and secondary flow, and promotes turbulent mixing of the two fluid streams. This enhances the power system by increasing the amount of fluid flow through the system, increasing the velocity at the rotor for more power availability, and reducing back pressure on turbine blades. Additional benefits include, among others, the reduction of noise propagating from the system.

[0034] The term "impeller" is used herein to refer to any assembly in which one or more blades are attached to a shaft and able to rotate, allowing for the generation of power or energy from fluid rotating the blades. Examples of impellers include a propeller or a rotor (which may be part of a rotor/stator assembly). Any type of impeller may be enclosed within the turbine shroud in the fluid turbine of the present disclosure.

[0035] The front of the fluid turbine indicates the direction from which fluid enters the fluid turbine. The leading edge of a turbine shroud may be considered the front of the fluid turbine, and the trailing edge of an ejector shroud may be considered the rear of the fluid turbine. A first component of the fluid turbine located closer to the front of the turbine may be considered "upstream" of a second component located closer to the rear of the turbine. Put another way, the second component is "downstream" of the first component.

[0036] The present disclosure relates to shrouded fluid turbines having an ejector shroud downstream of a turbine shroud. The axial length of the ejector shroud is much shorter than in prior versions, which provides an unexpected increase in the efficiency of the fluid turbine.

[0037] FIGS. 1-8 are various views of a first example embodiment of a shrouded fluid turbine of the present disclosure. Referring to FIG. 1, the shrouded wind turbine 100 comprises an aerodynamically contoured turbine shroud 110, an aerodynamically contoured nacelle body 150, an impeller 140, and an aerodynamically contoured ejector shroud 120. The turbine shroud 110 includes a front end 112, also known as an inlet end. The turbine shroud 110 also includes a rear end 114, also known as an exhaust end. The ejector shroud 120 includes a front end or inlet end 122, and a rear end or exhaust end 124. Support members 106 are shown connecting the turbine shroud 110 to the ejector shroud 120.

[0038] The rotor 146 surrounds the nacelle body 150. Here, the impeller 140 is a rotor/stator assembly comprising a stator 142 and a rotor 146. The rotor 146 is downstream and co-axial with the stator 142. The rotor 146 comprises a central hub 141 at the proximal end of the rotor blades. The central hub 141 is rotationally engaged with the nacelle body 150. The nacelle body 150 is connected to the turbine shroud 110 through the stator 142, or by other aerodynamically neutral support structures. A central passageway 152 extends through the nacelle body 150.

[0039] Some variations on the placement of the rotor and stator are not shown here, but are contemplated as being within the scope of this disclosure. In one variation, the stator 142 is downstream of the rotor 144. In another variation, the stator 142 and rotor 144 engage the nacelle body 150 at the rear end 114 of the turbine shroud (i.e. at the downstream end of the nacelle body), or possibly at the inlet end 122 of the ejector shroud (depending on the length of the nacelle body). In such embodiments, the stator may be connected to the ejector shroud 120 instead of the turbine shroud 110.

[0040] The turbine shroud has the cross-sectional shape of an airfoil with the suction side (i.e. low pressure side) on the interior of the shroud. The rear end 114 of the turbine shroud also has mixing lobes 116. The mixing lobes extend downstream beyond the rotor blades. Put another way, the trailing edge 118 of the turbine shroud is formed from a plurality of mixing lobes. The rear or downstream end of the turbine shroud is shaped to form two different sets of mixing lobes. High energy mixing lobes 117 extend inwardly towards the central axis 105 of the mixer shroud. Low energy mixing lobes 119 extend outwardly away from the central axis 105. These mixing lobes are more easily seen in FIG. 4 and FIGS. 6-8.

[0041] A mixer-ejector pump (indicated by reference numeral 101, FIG. 5) comprises an ejector shroud 120 surrounding the ring of high energy mixing lobes 117 and low energy mixing lobes 119 on the turbine shroud 110. The mixing lobes may extend downstream and into an inlet end 122 (see FIG. 1) of the ejector shroud 120. In accordance with other embodiments, the mixing lobes 116 may be separated from the inlet end 122 of the ejector shroud 120 by a gap (not shown).

[0042] Referring now to FIG. 1 and FIG. 2, the turbine shroud 110 has an axial length LM- The ejector shroud 120 has an axial length L_E. The entire turbine itself has an axial length Ι_τ. The turbine shroud 110 has a throat diameter D_F. This throat diameter DF is measured as the smallest diameter of the turbine shroud, and is generally located near the rotor 146. The rear end 114 of the turbine shroud has an inner diameter D and an outer diameter D O. The inner diameter D_Ri is measured as the diameter of a circle formed by the trailing edges of the high energy mixing lobes 117. Similarly, the outer diameter D_RO is measured as the diameter of a circle formed by the trailing edges of the low energy mixing lobes 119. It should be recognized that generally DF>D_RI, D_RO>D_RI, and DRO>D_f. These diameters are also depicted in FIG. 9.

[0043] The ejector shroud 120 also has a throat diameter D|. This throat diameter Di is measured as the smallest diameter of the ejector shroud, and is generally located near the inlet end 122. The ejector shroud 120 also has an outer diameter DE at the exhaust end 124. This outer diameter is measured as the diameter of a circle formed by the trailing edge 128 of the ejector shroud 120.

[0044] Due to the overlap of the turbine shroud and the ejector shroud, Ι_τ > LM + I_E. In embodiments, the ratio of L to I_E is from 0.05 to 2.5, including from 0.16 to

2.1 (0.05 <— < 2.5, including .16 < ^ < 2.1). The ratio of L_M to L_T may be from

0.1 to 1.0 (0.1 < ≤ 1.0). The ratio of L_E to L_T may be from 0.05 to 0.9 (0.05≤ ½ < 0.9).

[0045] The ratio of the ejector shroud length I_E to throat diameter Di may be from 0.05 to 3 (0.05 < < 3). The ratio of the ejector shroud length I_E to outer diameter

D_E may be from 0.05 to 3 (0.05 < ^ < 3).

[0046] The ratio of the turbine shroud length LM to throat diameter Dp may be from 0.1 to 2.5 (0.1 <— < 2.5).

Op The ratio of the turbine shroud length LM to the rear end outer diameter D_R0 may be from 0.1 to 1.25 (0.1 <— < 1.25.) The ratio of the

DRO

turbine shroud length LM to the rear end inner diameter DRI may be from 0.1 to 3.5 (0.1 < ≤ 3.5). The ratio of D_R0 to D_R, may be from 0.7 to 2 (0.7 < < 2). The nacelle body 150 plug trailing edge included angle AN (FIG. 1) will be thirty degrees or less. The length to diameter (L/D) of the overall wind turbine, or in other words, the ratio of L_T to D_E) will be from 0.05 to 3.0 (0.05 < ^ < 3.0).

[0047] The turbine shroud's entrance area and exit area will be equal to or greater than that of the annulus occupied by the rotor. The internal flow path cross-sectional area formed by the annulus between the nacelle body and the interior surface of the turbine shroud is aerodynamically shaped to have a minimum cross-sectional area at the plane of the turbine and to otherwise vary smoothly from their respective entrance planes to their exit planes. The ejector shroud entrance area is greater than the exit plane area of the turbine shroud. [0048] Referring to FIG. 6, the cross-sectional area of the throat of the turbine shroud 110 is represented by the grid area 154. Referring to FIG. 7, the exit area of the turbine shroud at the trailing edge 114 is represented by the grid area 156. Referring to FIG. 8, the exit area of the ejector shroud at the trailing edge 128 of the ejector shroud 120 is represented by grid area 158. The area ratio of the ejector pump, as defined by the ejector shroud exit area 158 over the turbine shroud exit area 156, may be in the range of 1.25-3.0. The number of each type of mixing lobe (high energy lobes or low energy lobes) can be between 6 and 28. The height-to- width ratio of the lobe channels may be between 0.5 and 5.0. The mixing lobe penetration may be between 30% and 80%.

[0049] The turbine shroud 110 has a set of high energy mixing lobes 117 that extend inwards toward the central axis 105 of the turbine. The turbine shroud also has a set of low energy mixing lobes 119 that extend outwards away from the central axis. The high energy mixing lobes alternate with the low energy mixing lobes around the trailing edge 118 of the turbine shroud. The impeller 140, turbine shroud 110, and ejector shroud 120 are coaxial with each other, i.e. they share a common central axis 105.

[0050] Referring to FIG. 9, the trailing edge 118 of the turbine shroud 110 has a circular crenellated shape. The trailing edge can be described as including several inner circumferentially spaced arcuate portions 182 which each have the same radius of curvature. Those inner arcuate portions 182 are evenly spaced apart from each other. Between portions 182 are several outer arcuate portions 184, which each have the same radius of curvature. The radius of curvature for the inner arcuate portions 182 is different from the radius of curvature for the outer arcuate portions 184, but the inner arcuate portions and outer arcuate portions have the same center (i.e. along the central axis 105). The inner arcuate portions 182 and the outer arcuate portions 184 are then connected to each other by radially extending portions 186. This results in a circular crenellated shape. The term "crenellated" as used herein does not require the inner arcuate portions, outer arcuate portions, and radially extending portions to be straight lines, but instead refers to the general up- and-down or in-and-out shape of the trailing edge. This crenellated structure forms two sets of mixing lobes, high energy mixing lobes 117 and low energy mixing lobes 119. [0051] Referring now to FIG. 1, free stream fluid (indicated generally by arrow 160, and which may be, for example, air or water) passing through the stator 142 has its energy extracted by the rotor 146. High energy fluid indicated by arrow 162 bypasses the turbine shroud 110 and stator 142, flows over the exterior of the turbine shroud 110, and is directed inwardly by the high energy mixing lobes 117. The low energy mixing lobes 119 cause the low energy fluid exiting downstream from the rotor 140 to be mixed with the high energy fluid 162. The high energy fluid 162 enters the ejector shroud 120. The ejector shroud camber creates a relatively lower pressure on the inner surface of the ejector, in the proximity of the leading edge 122, compared to the pressure on the outside of the ejector shroud 120. The lower pressure on the interior of the forward portion of the ejector shroud serves to draw in additional fluid flow that is further mixed with the high and low energy streams. An increase in pressure occurs on the interior of the ejector shroud as the mixing flow moves from the leading edge to the trailing edge of the ejector shroud. Put another way, an increase in pressure occurs on the interior of the ejector shroud as the flow moves from the upstream end of the ejector shroud to the downstream end of the ejector shroud. Airflow exiting the ejector shroud returns to ambient pressure. The ejector shroud 120 has a ring airfoil shape and does not have mixing lobes. In some embodiments, mixing lobes may also be formed on the trailing edge 128 of the ejector shroud 120.

[0052] Referring now to FIG. 11, a tangent line 171 is drawn along the interior surface at the trailing edge of the high energy mixing lobe 117. A rear plane 173 of the turbine shroud 110 is present. The point where the tangent line 171 intersects the rear plane 173 is indicated here with reference numeral 172. A line 174 is formed at point 172 parallel to the central axis 105. An angle 0₂ is formed by the intersection of tangent line 171 and line 174. This angle 0₂ is between 5 and 65 degrees. Put another way, a high energy mixing lobe 117 forms an angle 0₂ between 5 and 65 degrees relative to a longitudinal axis that is parallel to the central axis 105 of the turbine. In particular embodiments, the angle 0₂ is from about 30° to about 50°.

[0053] In FIG. 12, a tangent line 176 is drawn along the interior surface at the trailing edge of the low energy mixing lobe 119. The point where the tangent line 176 intersects the rear plane 173 is indicated here with reference numeral 179. A line 175 is formed at point 179 parallel to the central axis 105. An angle 0 is formed by the intersection of tangent line 176 and line 175. This angle 0 is between 5 and 65 degrees. Put another way, a low energy mixing lobe 1 19 forms an angle 0 between 5 and 65 degrees relative to a longitudinal axis that is parallel to the central axis 105 of the turbine. In particular embodiments, the angle 0 is from about 20° to about 45°.

[0054] Mixing lobes are present on the turbine shroud. As shown in FIG. 3, the ejector shroud 120 has a ring airfoil shape and does not have mixing lobes. If desired, though, mixing lobes may also be formed on a trailing edge 128 of the ejector shroud.

[0055] Referring now to FIG. 13 and FIG. 14, cross-sectional views of a second example embodiment of the shrouded fluid turbine are shown. Again, the wind turbine 200 comprises a turbine shroud 210 that has a front end 212 and a rear end 214. High energy mixing lobes 217 and low energy mixing lobes 219 are present around the rear end 214. The ejector shroud 220 has an inlet end 222 and an exhaust end 224. Support members 206 connect the turbine shroud 210 to the ejector shroud 220. The turbine 200 further comprises, similarly, an impeller 240, stator 242, rotor 246, and a nacelle body 250. A central passageway 252 extends through the nacelle body 250.

[0056] The turbine shroud 210 has an axial length L_M. The ejector shroud 220 has an axial length I_E2- The entire turbine itself has an axial length Ι_τ2· The turbine shroud 210 has a throat diameter DF. This throat diameter D_F is measured as the smallest diameter of the turbine shroud, and is generally located near the rotor 246. The rear end 214 of the turbine shroud has an inner diameter Dm and an outer diameter DRO- The inner diameter D_R( is measured as the diameter of a circle formed by the high energy mixing lobes 217. Similarly, the outer diameter D_RO is measured as the diameter of a circle formed by the low energy mixing lobes 219.

[0057] The ejector shroud 220 also has a throat diameter D|. This throat diameter Di is measured as the smallest diameter of the ejector shroud, and is generally located near the inlet end 222. The ejector shroud 220 also has an outer diameter DE at the exhaust end 224. This outer diameter is measured as the diameter of a circle formed by the trailing edge 228 of the ejector shroud 220.

[0058] The notations L_E2 and Ly₂ are used to indicate that the lengths of the ejector shroud 220 and the overall turbine 200 differ from the lengths LE and Lj shown in the embodiment depicted in FIG. 1 -5. The values for L_M, D_F, D , DRO, DI, and D_E are the same for both the embodiments of FIG. 5 and FIG. 14. This notation relates to FIG. 15 and FIG. 16, as explained further below.

[0059] Comparative calculations were performed on the two embodiments depicted in FIGS. 1-14. FIG. 15 and FIG. 16 show and explain the results of the calculations.

[0060] FIG. 15 is a cross-sectional view comparing the first example embodiment of FIG. 1 with the second example embodiment of FIG. 13. The upper half is the embodiment shown in FIG. 1 , and the bottom half is the embodiment shown in FIG. 13. This is indicated by the use of the different reference numerals to refer to the turbine shroud (110, 220), the ejector shroud (120, 220), and the nacelle body (150, 250).

[0061] For the comparative calculations, the throat diameter DF was kept constant between both embodiments, as was the ejector shroud outer diameter DE. The axial length LM was also kept constant. In addition, the length of overlap between the turbine shroud and the ejector shroud L_ME was kept constant. L_E is greater than L_E2.

[0062] FIG. 16 is a graph showing power output versus the wind velocity for the two different turbines. The power output is intended to show the relative amount of energy captured from the wind stream passing through the turbine shroud. The relative values in this graph were generated by data gathered in a wind tunnel. The first set of values (squares) were generated from a wind turbine having the relatively longer ejector shroud axial length L_E. The ratio of L_E/D_E was 0.32.

[0063] The second set of values (circles) were generated from a wind turbine having the relatively shorter ejector shroud axial length L_E2. The ratio of L_E2/D_E was 0.12. As seen in FIG. 16, a shorter ejector shroud generated more power at the same wind velocity.

[0064] The present disclosure has been described with reference to example embodiments. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the present disclosure be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.

Claims

CLAIMS:

1. A fluid turbine (100) comprising a turbine shroud (110) and an ejector shroud (120);

wherein the turbine shroud has a front end (112) and a rear end

(114);

wherein the ejector shroud has an inlet end (122) and an exhaust end (124);

wherein the rear end of the turbine shroud comprises a plurality of mixing lobes (116) along a trailing edge (118);

wherein the turbine shroud has an axial length L ;

wherein the ejector shroud has an axial length L_E; and wherein the ratio of LM to LE is from 0.05 to 2.5.

2. The fluid turbine of claim 1 , wherein the mixing lobes extend into the inlet end of the ejector shroud.

3. The fluid turbine of claim 1 , wherein the ratio of LM to L_E is from 0.16 to 2.1.

4. The fluid turbine of claim 1 , wherein the ejector shroud has an outer diameter D| at the inlet end, and the ratio of L_E to D| is from 0.05 to 3.0.

5. The fluid turbine of claim 1 , wherein the ejector shroud has an outer diameter DE at the exhaust end, and the ratio of L_E to D_E is from 0.05 to 3.0.

6. The fluid turbine of claim 1 , wherein the turbine shroud has an outer diameter DF at the front end, and the ratio of L_M to D_F is from 0.1 to 2.5.

7. The fluid turbine of claim 1 , wherein the turbine shroud has an outer diameter DRO at the rear end, and the ratio of L_M to D_RO is from 0.1 to 1.25.

8. The fluid turbine of claim 1 , wherein the turbine shroud has an inner diameter DR_I at the rear end, and the ratio of L_M to DR_I is from 0.1 to 3.5.

9. The fluid turbine of claim 1 , wherein the rear end of the turbine shroud has an inner diameter DRI and an outer diameter DRO, and the ratio of DRO to D _I is from 0.7 to 2.

10. The fluid turbine of claim 1 , wherein the fluid turbine has a total axial length Ι_τ, and the ratio of LM to bp is from 0.05 to 1 .0.

1 1. The fluid turbine of claim 1 , wherein the fluid turbine has a total axial length Ι_τ, and the ratio of 1_E to LT is from 0.05 to 0.9.

12. The fluid turbine of claim 1 , wherein the ejector shroud has a ring airfoil shape and does not have mixing lobes.

13. The fluid turbine of claim 1 , wherein the plurality of mixing lobes includes a set of high energy mixing lobes (1 17) and a set of low energy mixing lobes (1 19), the high energy mixing lobes having an angle of about 35° to about 50° relative to a longitudinal axis (105) of the turbine shroud.

14. A fluid turbine (100) comprising a turbine shroud (110) and an ejector shroud (120);

wherein the turbine shroud has a front end (112) and a rear end

(114);

wherein the ejector shroud has an inlet end (122) and an exhaust end (124);

wherein the rear end of the turbine shroud comprises a plurality of mixing lobes ( 6) along a trailing edge (118);

wherein the turbine shroud has an axial length LM;

wherein the ejector shroud has an axial length LE, an outer diameter Di at the inlet end, and an outer diameter DE at the exhaust end;

wherein the ratio of L_M to LE is from 0.05 to 2.5;

wherein the ratio of LE to D| is from 0.05 to 3; and

wherein the ratio of LE to DE is from 0.05 to 3.

15. The fluid turbine of claim 14, wherein the mixing lobes extend into the inlet end of the ejector shroud.