Turbine runner flow deflectors

Abstract

A runner for a turbine includes a set of blades coupled at a first end to a crown of the runner and coupled at a second end to a band, wherein the set of blades are configured to direct a flow of fluid from a fluid inlet of the turbine to a fluid outlet of the turbine, and wherein adjacent blades of the set of blades form channels for the flow of fluid, and a set of flow deflectors, each flow deflector disposed within a channel and separated from at least one of the adjacent blades and coupled to the band, wherein the flow deflectors are configured to adjust a direction of the flow of fluid in the channels.

Description

TURBINE RUNNER FLOW DEFLECTORSRELATED APPLICATION

[0001] The present application claims priority from and the benefit of U.S. Provisional Patent Application No. 63 / 558,488, filed February 27, 2024, the disclosure of which is hereby incorporated herein by reference in full.FIELD

[0002] The present application is directed to water turbines, and in particular components of water turbines.BACKGROUND

[0003] Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted to being prior art by inclusion in this section.

[0004] A Francis turbine is one type of water turbine that operates on the principle of converting the kinetic energy of water into mechanical energy. In operation, water flows from a high-pressure source, often a reservoir or dam, through a spiral-shaped casing called the scroll case or through a spiral casing or a semi-spiral shaped casing. The water is then directed towards the runner, which consists of a set of curved blades. As the high-velocity water strikes the blades, it causes the runner to spin. The curved design of the blades, characteristic of the Francis turbine, allows it to harness both the kinetic energy of the flowing water and the potential energy associated with the water's pressure. The spinning motion of the runner is transferred to a shaft, which, in turn, drives a generator to produce electricity.

[0005] Francis turbines are widely used for hydropower generation due to their efficiency and versatility. However, these turbines are susceptible to cavitation-related issues, particularly onthe runner. Cavitation occurs when the pressure of the water drops below the vapor pressure, leading to the formation and subsequent collapse of vapor bubbles on the runner's surface. This cyclic process can cause erosion and pitting on the runner blades, compromising the structural integrity and efficiency of the turbine over time.

[0006] The cavitation problems associated with Francis turbine runners can be exacerbated by factors such as high water flow rates, improper design, and suboptimal operational conditions. Excessive cavitation can lead to material damage, reducing the lifespan of the runner and necessitating costly repairs.SUMMARY

[0007] Apparatuses and methods for improving the performance of a turbine using flow deflectors are provided.

[0008] According to various aspects there is provided a runner for a turbine. In some aspects, the runner may include a set of blades coupled at a first end to a crown of the runner and coupled at a second end to a band, where the set of blades are configured to direct a flow of fluid from a fluid inlet of the turbine to a fluid outlet of the turbine and wherein adjacent blades of the set of blades form channels for the flow of fluid; and a set of flow deflectors (also referred to herein as fins), each flow deflector disposed within a channel and separated from at least one of the adjacent blades and coupled to the band, where the flow deflectors are configured to adjust a direction of the flow of fluid in the channels.

[0009] According to various aspects there is provided a flow deflector for a hydraulic turbine runner. In some aspects, the flow deflector may include a first end and a second end disposed distally from the first end along a length; a top surface distally disposed from a bottom surface, the bottom surface configured for coupling to a band of the hydraulic turbine runner.

[0010] The flow deflector may have a curvature along the length that approximately corresponds to a curvature of an adjacent blade of the hydraulic turbine runner, and the flow deflector may have a height from the bottom surface to the top surface less than a height of the blade of the hydraulic turbine runner as determined between the band and a crown of the hydraulic turbine runner.

[0011] According to various aspects there is provided a method for improving performance of a turbine. In some aspects, method may include providing a set of flow deflectors in channels between adjacent blades of a turbine runner; and coupling each flow deflector of the set of flow deflectors to a band of the turbine runner separated from at least one adjacent blade, each flow deflector having a curvature that approximately corresponds to a curvature of the at least one adjacent blade and a height from the band less than a height of the at least one adjacent blade. Each flow deflector may guide a flow of fluid through the channel.BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Aspects and features of the various embodiments will be more apparent by describing examples with reference to the accompanying drawings, in which:

[0013] FIG. 1 is a diagram illustrating an example of a Francis hydraulic turbine according to some aspects of the present disclosure;

[0014] FIG. 2 is a diagram illustrating an example of a Francis turbine runner showing a fin location according to some aspects of the present disclosure;

[0015] FIG. 3 A is a top view of an example of a fin according to some aspects of the present disclosure;

[0016] FIG. 3B is a side view of an example of a fin according to some aspects of the present disclosure;

[0017] FIG. 4A is a top view of an example of a fin illustrating details of the fin according to some aspects of the present disclosure; and

[0018] FIG. 4B is a side view of an example of a fin illustrating additional details of the fin according to some aspects of the present disclosure;

[0019] FIG. 5 is a diagram illustrating an example of a fin coupled to an adjacent runner blade according to some aspects of the present disclosure;

[0020] FIG. 6 is a flowchart illustrating an example of a method for improving the performance of a turbine according to some aspects of the present disclosure; and

[0021] FIG. 7 is a top view of another example of a fin illustrating details of the fin according to some aspects of the present disclosure.DETAILED DESCRIPTION

[0022] While certain embodiments are described, these embodiments are presented by way of example only, and are not intended to limit the scope of protection. The apparatuses, methods, and systems described herein may be embodied in a variety of other forms. Furthermore, various omissions, substitutions, and changes in the form of the example methods and systems described herein may be made without departing from the scope of protection.

[0023] Similar reference characters indicate corresponding parts throughout the several views unless otherwise stated. Although the drawings represent embodiments of various features and components according to the present disclosure, the drawings are not necessarily to scale and certain features may be exaggerated in order to better illustrate embodiments of the present disclosure, and such exemplifications are not to be construed as limiting the scope of the present disclosure.

[0024] Except as otherwise expressly stated herein, the following rules of interpretation apply to this specification: (a) all words used herein shall be construed to be of such gender or number (singular or plural) as circumstances require; (b) the singular terms “a,” “an,” and “the,” as used in the specification and the appended claims include plural references unless the context clearly dictates otherwise; (c) the antecedent term “about” applied to a recited range or value denotes an approximation within the deviation in the range or values known or expected in the art from the measurements; (d) the words “herein,” “hereby,” “hereto,” “hereinbefore,” and “hereinafter,” and words of similar import, refer to this specification in its entirety and not to any particular paragraph, claim, or other subdivision, unless otherwise specified; (e) descriptive headings are for convenience only and shall not control or affect the meaning or construction of any part of the specification; and (f) “or” and “any” are not exclusive and “include” and “including” are not limiting. Further, the terms, “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including but not limited to”).

[0025] Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range or within any sub ranges there between, unless otherwise clearly indicated herein. Each separate value within a recited range is incorporated into the specification or claims as if each separate value were individually recited herein. Where a specific range of values is provided, it is understood that each intervening value, to the tenth or less of the unit of the lower limit between the upper and lower limit of that range and any other stated or intervening value in that stated range or sub range hereof, is included herein unless the context clearly dictates otherwise. All subranges are also included. The upper and lower limits of these smaller ranges are also included therein, subject to any specifically and expressly excluded limit in the stated range.

[0026] FIG. 1 is a diagram illustrating an example of a Francis hydraulic turbine 100. Some aspects of the present disclosure may be implemented using a Francis hydraulic turbine, such as the exemplary one shown in FIG. 1. The Francis hydraulic turbine 100 may be configured to convert hydraulic energy to torque to drive an electrical generator (not shown) through a turbine shaft 104. Fluid, typically water flows through a casing 102 into a distributor 113 surrounding a rotating runner 103 of the hydraulic turbine 100. The distributor 113 may have stay vanes 132 and guide vanes 130. Water flows inward into the runner 103 in a generally spiraling motion along a typically predominantly radial direction inside a turbine having an axis 111. The rotational velocity of the water drives the runner 103 to turn around the axis 111. As the water flows through the runner 103, the transport component of the water is turned from a predominantly radial flow to a generally coaxial outflow. From the runner 103, water flows into a draft tube 105 below the runner 103.

[0027] The runner 103 of a turbine may include a crown 106 and a band 108 both having a surface of revolution around the axis 111 of the runner 103, and blades 107 extending out from the surface of revolution of the crown 106 to a band 108. Each blade 107 has a leading edge and a trailing edge. The ends of these edges are joined to the crown 106 and the band 108. The runner 103 may be located above a bottom ring 122 in the hydraulic turbine 100, as shown in the example of Fig. 1. Water enters the runner 103, flows around the leading edges of the blades, flows between the blades 107, and passes over the trailing edges of the blades, then flows into the draft tube 105.

[0028] According to some aspects of the present disclosure, fins, also referred to herein as flow deflectors, may be disposed on an internal surface of the band of a turbine runner within a channel formed by adjacent blades. The flow deflectors may adjust the directional flow of the fluid through the channel thereby maximizing power and / or efficiency and ensuring structural integrity by preventing cavitation damage to the turbine runner. The flow deflectors may also be effective at achieving other desirable effects, such as wider turbine operating ranges and lower pressure pulsations. In hydraulic turbines the flow deflectors may reduce cavitation damage to the runner and provide natural aeration of the fluid. In addition, the flow deflectors may allow for the use of fewer main runner blades since some of the flow guidance can be taken over by the fins.

[0029] FIG. 2 is a diagram illustrating an example of a Francis turbine runner 200 showing a fin location according to some aspects of the present disclosure. The terms “Francis turbine” and “turbine” may be used interchangeably throughout the disclosure to describe the Francis turbine. As shown in FIG. 2, blades 230a, 230b of the turbine runner 200 may extend from the crown 202 to the band 220. The attachment points 235 of the blades 230a, 230b to the band 220 are illustrated in FIG. 2. Fluid may enter the turbine runner 200 at the leading edge 231 of the blades and may exit the turbine runner 200 at the trailing edge 233 of the blades.

[0030] Referring to FIG. 2, flow deflectors 210, may be disposed on an inner surface 222 of the band 220. The terms flow deflector and fin are used interchangeably herein. The fins may be disposed within a channel 232 formed between adjacent blades 230a, 230b of the turbine runner 200. In some implementations, a fin may be disposed in each channel formed between pairs of adjacent blades. In some implementations, a fin may be disposed in less than each channel formed between pairs of adjacent blades. In some implementations, more than one fin may be disposed in a channel. In some implementations, the fins have a similar shape and size. In other implementations, the fins may have different shapes and sizes. FIG. 2 illustrates the attachment points 214 of the fins 210 to the band 220. The fins may be attached to the band using a variety of methods. For example, the fins may be part of the casting or may be welded or bolted to the band. The fins 210 may have any height between the band 220 and the crown 202 but are not attached to the crown 202.

[0031] FIG. 3 A is a top view of an example of a fin 210 according to some aspects of the present disclosure. FIG. 3B is a side view of an example of a fin 210 according to some aspects of the present disclosure. As illustrated in FIGS. 3A and 3B, the fin 210 may be disposed on the inner surface 222 of the band 220 closer to one or the other adjacent blades 230a, 230b or may be centered between the adjacent blades 230a, 230b. The fin 210 may be disposed substantially equidistant from an upper (inlet) edge 224 of the band 220 and a lower (outlet) edge 226 of the band 220 or may be disposed closer to the upper (inlet) edge 224 of the band 220 or the lower (outlet) edge 226 of the band 220. In some implementations as discussed below in connection with FIG. 7, the fins 210 may extend beyond the channel at the upper (inlet) edge 224 of the band 220 and / or at the lower (outlet) edge 226 of the band 220.

[0032] FIG. 4A is a top view of an example of a fin illustrating details of the fin 210 according to some aspects of the present disclosure. Referring to FIG. 4A, the fin 210 may be disposed on an inner surface 222 of the band 220 in a spanwise position 450 (i.e., in a direction between adjacent blades 230a, 230b) closer to one or the other adjacent blades 230a, 230b or may be centered between the adjacent blades 230a, 230b. The fin 210 may be disposed on an inner surface 222 of the band 220 in a streamwise position 460 (i.e., in a direction between the upper (inlet) edge 224 of the band 220 and the lower (outlet) edge 226 of the band 220) substantially equidistant from an upper (inlet) edge 224 of the band 220 and a lower (outlet) edge 226 of the band 220 or may be disposed closer to the upper (inlet) edge 224 of the band 220 or the lower (outlet) edge 226 of the band 220.

[0033] The fin 210 may have a length 410 as measured from an upper (inlet) edge 224 of the band 220 to a lower (outlet) edge 226 of the band 220. The length 410 of the fin 210 may be proportional to the length of an adjacent blade 230a as measured from an upper (inlet) edge 224 of the band 220 to a lower (outlet) edge 226 of the band 220. For example, the fin 210 may have a length 410 substantially equal to or slightly longer than the length of an adjacent blade 230a or may have a length less than the length of an adjacent blade 230a.

[0034] The length 410 of the fin 210 should be long enough to direct the fluid flow through the channel and have an impact on the streamlines of the flow. However, too long of a fin can increase the friction on the surface of the fin 210 resulting in a reduction of turbine efficiency. In some implementations, the length 410 of the fin 210 may be less than a length of an adjacentblade 230a. In some implementations, the length 410 of the fin 210 may be substantially the same as the length of an adjacent blade 230a. In some implementations, the fin 210 will be short in comparison with the adjacent blade 230a, i.e., less than half the length of the adjacent blade.

[0035] The fin 210 may have a curvature 420 substantially equal to a local curvature of an adjacent blade 230a or may have a curvature 420 different than the local curvature of an adjacent blade 230a to achieve specific effects on the fluid flow. A minimum thickness of the fin in a thickness direction 430 may be determined based on structural requirements needed to withstand forces generated by fluid and flow conditions. The fin 210 may have any thickness distribution. For example, a fin may have a thickness distribution where the fin has a different thickness at the leading edge than at the trailing edge. Alternatively, the thickness distribution may be approximately the same from leading edge to trailing edge.

[0036] The angle 440 of the fin 210 with respect to an adjacent blade, for example adjacent blade 230a, may be set such that the fin 210 is substantially parallel to the adjacent blade 230a. The angle 440 of the fin 210, as well as the pivot point or axis of rotation of the fin, can be adjusted to achieve specific effects on the fluid flow.

[0037] FIG. 4B is a side view of an example of a fin illustrating additional details of the fin 210 according to some aspects of the present disclosure. The fin 210 may have a height 470 from a bottom surface 211 of the fin 210 configured to be coupled to the inner surface 222 of the band 220 to a top surface 213 of the fin 210. The fin 210 may have any height less than the band-to-crown height of an adjacent blade 230a. The height 470 of the fin 210 can influence the pressure distribution in the band-to-crown direction and / or in the streamwise direction on the adjacent blade 230a. A fin 210 having insufficient height may not direct the flow enough and the influence of the fin would be insufficient. A fin 210 that is too tall may be structurally weak and can introduce increased energy losses to the turbine.

[0038] The leading edge 212 of the fin 210 may include an inlet angle, such as bevel angle 480. The leading edge 212 of the fin 210 may be closest to the upper (inlet) edge 224 of the band 220. The bevel angle 480 is added on the leading edge 212 of the fin 210 to provide a progressive transition of the upstream flow around the fin 210. The bevel angle 480 may be an acute angle as determined perpendicular to the inner surface 222 of the band 220. The fin 210 may have any bevel angle 480 and thickness distribution. The leading edge 212 of the fin 210may have other configurations including, but not limited to an inlet radius or a continuously varying surface curvature.

[0039] In some implementations, fins may be coupled to an adjacent runner blade. FIG. 5 is a diagram illustrating an example of a fin 510 coupled to an adjacent runner blade according to some aspects of the present disclosure. Referring to FIG. 5, the fins 510 may be disposed on an inner surface 222 of the band 220. The fins may be disposed within a channel formed between adjacent blades of the turbine and may be coupled to one of the adjacent blades 230a. In some implementations, a fin may be disposed in each channel formed between pairs of adjacent blades. In some implementations, a fin may be disposed in less than each channel formed between pairs of adjacent blades. As shown in FIG. 5, the fin 510 may include an angled portion 520 configured to couple the fin 510 to one of the adjacent blades 230a. The angled portion 520 may be formed at a substantially 90° angle or another angle.

[0040] FIG. 7 is a top view of an example of a fin 710 that extends past an edge of the band according to some aspects of the present disclosure. As illustrated in FIG. 7, the fin 710 may be partially disposed on the inner surface 222 of the band between adjacent blades 230a, 230b and extend past the outlet edge 226. FIG. 7 illustrates an implementation where the fin extends into the draft tube at the outlet of the runner. One advantage of a fin that extends past the outlet edge is that the wake is shed in the draft tube. In some implementations, the fin may be partially disposed on the inner surface 222 of the band between adjacent blades 230a, 230b and extend past the inlet edge of the band. In some implementations, the fin may extend past both the inlet edge and the outlet edge of the band.

[0041] The parameters of a fin generally include height, length, and profile shape. The profile shape includes an inlet angle or radius at the leading edge of the fin, an outlet angle or radius at the opposite edge of the fin, a curvature or angular distribution along the length of the fin, and a thickness distribution. The parameters of a fin may be selected to guide the flow to reduce cavitation and / or improve efficiency. In one example the fin parameters included a curvature substantially equal to the adjacent part of the blade, a thickness distribution with a relatively thin average thickness compared to the adjacent blade, a bevel at the inlet (leading edge) and outlet (opposite edge) of the fin, a height of the fin normal to the band of approximately 5% of the blade outlet edge length, and a fin length of approximately 40% of the blade length inthroughflow direction on the band. A runner with fins having these parameters reduced vortices in certain areas as compared to a runner without fins. Since the vortices contributed to cavitation, the fins reduced cavitation by reducing the vortices. The fins also at least partially blocked and thus reduced secondary flow from the pressure to suction side across the band, which improved efficiency. In some implementations, the parameters may be selected to balance the cavitation and efficiency effects. In other implementations, the parameters may be selected to favor one of the effects over the other.

[0042] FIG. 6 is a flowchart illustrating an example of a method 600 for improving the performance of a turbine according to aspects of the present disclosure. Referring to FIG. 6, at block 610, fins may be provided for the turbine runner. The fins may be provided on new turbine runners or may be retrofit to existing turbine runners.

[0043] The fin may have a length as measured from an upper (inlet) edge of the band to a lower (outlet) edge of the band. The length of the fin may be proportional to the length of an adjacent blade as measured from an upper (inlet) edge of the band to a lower (outlet) edge of the band. The length of the fin should be long enough to direct the fluid flow through the channel and have an impact on the streamlines of the flow. The length of the fin may be less than or substantially the same as a length of an adjacent blade.

[0044] The fin may have any height less than the band-to-crown height of an adjacent blade. The leading edge of the fin may include a bevel angle to provide a progressive transition of the upstream flow around the fin. The fin may have any bevel angle and thickness distribution.

[0045] At block 620, the fins may be coupled to the band of the turbine runner. The fins may be disposed on an inner surface of the band. The fins may be disposed within a channel formed between adjacent blades of the turbine runner. In some implementations, a fin may be disposed in each channel formed between pairs of adjacent blades. In some implementations, a fin may be disposed in less than each channel formed between pairs of adjacent blades. In some implementations, more than one fin may be disposed in a channel.

[0046] The fin may be disposed on an inner surface of the band in a spanwise position closer to one or the other adjacent blades or may be centered between the adjacent blades. The fin may be disposed on the inner surface of the band in a streamwise position substantially equidistantfrom an upper (inlet) edge of the band and a lower (outlet) edge of the band or may be disposed closer to the upper (inlet) edge of the band or the lower (outlet) edge of the band.

[0047] The angle of the fin with respect to an adjacent blade may be set such that the fin is substantially parallel to the adjacent blade. The angle of the fin, as well as the pivot point or axis of rotation of the fin, can be adjusted to achieve specific effects on the fluid flow.

[0048] At block 630, the rotor with the fins coupled to the band may be provided for use in a turbine. The runner may be a new turbine runner with fins or may be an existing turbine runner that has been retrofit with the fins.

[0049] The specific operations illustrated in FIG. 6 provide a particular method for improving the performance of a turbine according to an embodiment of the present disclosure. Other sequences of operations may also be performed according to alternative embodiments. For example, alternative embodiments of the present disclosure may perform the operations outlined above in a different order. Moreover, the individual operations illustrated in FIG. 6 may include multiple sub-operations that may be performed in various sequences as appropriate to the individual operation. Furthermore, additional operations may be added or removed depending on the particular applications.

[0050] The examples and embodiments described herein are for illustrative purposes only. The fins may have shapes and relative dimensions and be placed in locations other than those shown or described above. The fins are not limited to having the same shape and size or being placed at the same location on a given runner. The dimensions and / or placement may vary. The fins may be used in turbines other than Francis hydraulic turbines, including pump turbines and turbines with spiral-shaped or semi-spiral shaped casings. Various modifications or changes in light thereof will be apparent to persons skilled in the art. These are to be included within the spirit and purview of this application, and the scope of the appended claims, which follow.

Claims

CLAIMSWHAT IS CLAIMED IS:

1. A runner for a turbine, the runner comprising: a set of blades coupled at a first end to a crown of the runner and coupled at a second end to a band, wherein the set of blades are configured to direct a flow of fluid from a fluid inlet of the turbine to a fluid outlet of the turbine, and wherein adjacent blades of the set of blades form channels for the flow of fluid; and a set of flow deflectors, each flow deflector disposed within a channel and separated from at least one of the adjacent blades and coupled to at least the band, wherein the flow deflectors are configured to adjust a direction of the flow of fluid in the channels.

2. The runner of claim 1, wherein the flow deflectors are disposed on an inner surface of the band of the runner in a specified position between an inlet edge of the band and an outlet edge of the band.

3. The runner of claim 1 or claim 2, wherein the flow deflectors are disposed on an inner surface of the band of the runner in a specified position between adjacent blades of the runner.

4. The runner of any previous claim, wherein the flow deflectors comprise a curvature substantially equal to a curvature of an adjacent blade of the runner.

5. The runner of any previous claim, wherein the flow deflectors comprise a height less than a height of the adjacent blades as determined between the band and the crown of the runner.

6. The runner of any previous claim, wherein the flow deflectors comprise a length less than a length of an adjacent blade as measured from an inlet edge of the band to an outlet edge of the band.

7. The runner of any previous claim, wherein the flow deflectors are disposed on an inner surface of the band of the runner at an angle substantially parallel to an adjacent blade.

8. The runner of any previous claim, wherein the flow deflectors extend past an inlet or an outlet edge of the band.

9. The flow deflector of any previous claim, wherein for each of the flow deflectors a thickness of the flow deflector varies along a length of the flow deflector.

10. A flow deflector for a hydraulic turbine runner, the flow deflector comprising: a first end and a second end disposed distally from the first end along a length; and a top surface distally disposed from a bottom surface, the bottom surface configured for coupling to a band of the hydraulic turbine runner, wherein the flow deflector has a curvature along the length, and wherein the flow deflector has a height from the bottom surface to the top surface less than a height of an adjacent blade of the hydraulic turbine runner as determined between the band and a crown of the hydraulic turbine runner.

11. The flow deflector of claim 10, wherein the flow deflectors comprise a length less than a length of an adjacent blade as measured from an inlet edge of the band to an outlet edge of the band.

12. The flow deflector of claim 10 or claim 11, wherein for each of the flow deflectors a thickness of the flow deflector varies along a length of the flow deflector.

13. The flow deflector of any of claims 10-12, wherein the flow deflectors are configured to be disposed on an inner surface of the band in a specified position between an inlet edge of the band and an outlet edge of the band.

14. The flow deflector of any of claims 10-13, wherein the flow deflectors are configured to be disposed on an inner surface of the band in a specified position between adjacent blades of the runner.

15. The flow deflector of any of claims 10-14, wherein the flow deflectors are configured to be disposed on an inner surface of the band at an angle substantially parallel to an adjacent blade.

16. The flow deflector of any of claims 10-15, wherein the flow deflectors are configured to be disposed on an inner surface of the band at an angle substantially different than an adjacent blade.

17. The flow deflector of any of claims 10-16, wherein the flow deflectors comprise a length substantially equal to a length of an adjacent blade as measured from an inlet edge of the band to an outlet edge of the band.

110. The flow deflector of any of claims 10-17, wherein the flow deflectors extend past an inlet or an outlet edge of the band.

11. A method for improving performance of a turbine, the method comprising: providing a set of flow deflectors in channels between adjacent blades of a turbine runner; and coupling each flow deflector of the set of flow deflectors to a band of the turbine runner separated from at least one adjacent blade, each flow deflector having a curvature that approximately corresponds to a curvature of at least one adjacent blade and a height from the band less than a height of the at least one adjacent blade, wherein each flow deflector guides a flow of fluid through the channel.

20. The method of claim 19, wherein coupling a flow deflector to the band comprises coupling the flow deflector in a specified position in relation to an inlet edge of the band and an outlet edge of the band.

21. The method of claim 19 or claim 20, wherein coupling a flow deflector to the band comprises coupling the flow deflector in a specified position in relation to one or the other adjacent blades.

12. The method of any of claims 19-21, wherein coupling a flow deflector to the band comprises coupling the flow deflector at an angle substantially parallel to an adjacent blade.

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