WO2011160210A2

WO2011160210A2 - Duct assembly for a cross-flow water turbine

Info

Publication number: WO2011160210A2
Application number: PCT/CA2011/000734
Authority: WO
Inventors: Voytek Roman Klaptocz; Yasser Nabavi
Original assignee: Mavi Innovations Inc.
Priority date: 2010-06-21
Filing date: 2011-06-21
Publication date: 2011-12-29
Also published as: WO2011160210A3

Abstract

A duct assembly for a cross-flow water turbine comprising two oppositely facing symmetrical ducts and a support assembly. Each duct comprises an active surface and a back surface. The active surface faces the turbine, protrudes away from the back surface, is symmetrical about a plane coplanar with the rotational axis of the turbine, and has an angle of attack at the leading and trailing edges of between 60 and 80 degrees. Each duct has a length of between 0.9 to 1.3 times the rotational diameter of the turbine and a width of between 0.35 to 0.6 times the rotational diameter of the turbine. The support assembly supports each duct such that the frontal width of the duct assembly is between 1.75 to 2.25 times the rotational diameter of the turbine.

Description

DUCT ASSEMBLY FOR A CROSS-FLOW WATER TURBINE

FIELD

[0001] The present disclosure generally relates to a duct assembly for a cross- flow water turbine.

BACKGROUND

[0002] Significant efforts have been made in the past few decades to identify and harness renewable energy sources. One area of particular interest has been the extraction of energy from water flows using water turbines. It has been found that placing ducting around the turbine to direct the water flow into and out of the turbine can produce increased power output from the turbine by increasing the velocity of the water flow traveling through the turbine, favourably controlling the direction of flow through the turbine, and increasing the pressure drop across the turbine.

[0003] A number of duct designs have focussed on minimizing flow separation and drag by utilizing narrow streamlined duct shapes. In order to maximize power output of the turbine these ducts tend to have lengths that exceed the rotor diameter of the turbine resulting in significant manufacturing costs due to the quantity of material and structural supports required to implement these designs.

SUMMARY

[0004] In one if its aspects, the present disclosure provides a duct assembly for a cross-flow water turbine, the duct assembly comprising:

(a) two oppositely facing symmetrical ducts, each duct comprising an active surface and a back surface, the active surface facing the turbine and protruding away from the back surface, the active surface symmetrical about a plane coplanar with the rotational axis of the turbine, the active surface having an angle of attack at the leading and trailing edges of between 60 to 80 degrees, each duct having a length of between 0.9 to 1.3 times the rotational diameter of the turbine and a width of between 0.35 to 0.6 times the rotational diameter of the turbine; and

(b) a support assembly supporting each duct such that the frontal width of the duct assembly is between 1.75 to 2.25 times the rotational diameter of the turbine.

[0005] Alternatively, the frontal width of the duct assembly may be between 1.8 to 2.2, 1.85 to 2.15, 1.9 to 2.1, 1.95 to 2.05, or 2 times the rotational diameter of the turbine; each duct may have a width of between 0.4 to 0.55, 0.42 to 0.48, or 0.44 times the rotational diameter of the turbine; each duct may have a length of between 0.95 to 1.2, 0.975 to 1.1, or 1 times the rotational diameter of the turbine; and/or the active surface of each duct may have an angle of attack at the leading and trailing edges of between 65 to 75, 67.5 to 72., or 70 degrees.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Figure 1 is a front isometric view of a plan view of a ducted turbine module according to an embodiment.

[0007] Figure 2 is a front isometric view of a duct assembly according to an embodiment.

[0008] Figure 3 is a cross-sectional top plan view of the duct assembly of the ducted turbine module shown in Figure 1.

[0009] Figure 4 is a cross-sectional top plan view of a duct assembly according to an embodiment.

[0010] Figure 5 is a front isometric view of the duct assembly of the ducted turbine shown in Figure 1 having the active surface of one of the ducts removed.

[001 1] Figure 6 is a cross-sectional top plan view of the duct assembly of the ducted turbine module shown in Figure 1 representing the flow separation region induced by the duct assembly. [0012] Figure 7 is a front isometric view of the ducted turbine module shown in

Figure 1 mounted to a floating platform.

[0013] Figure 8 is a side perspective view of the ducted turbine module shown in

Figure 1 tethered to a gravity base.

[0014] Figure 9 is a front isometric view of the ducted turbine module shown in

Figure 1 mounted to a gravity base.

[0015] Figure 10 is a front isometric view of a vertical stack of the ducted turbine modules shown in Figure 1.

[0016] Figure 11 is a front isometric view of a horizontal stack of the ducted turbine modules shown in Figure 1.

[0017] Figure 12 is a front isometric view of a horizontally spaced configuration of the ducted turbine modules shown in Figure 1.

[0018] Figure 13 is a cross-sectional top plan view of five duct assembly configurations according to embodiments.

DETAILED DESCRIPTION

[0019] As used herein, relative terms such as "horizontal," "vertical," "up,"

"down," "top" and "bottom" as well as derivatives thereof (e.g., "horizontally," "downwardly," "upwardly," etc.) should be construed to refer to the orientation as then described or as shown in the drawing figure under discussion. These relative terms are for convenience of description and are not intended to require a particular orientation.

[0020] The embodiments described herein relate to a duct assembly for a cross- flow water turbine. In particular, the embodiments relate to a duct assembly comprising ducts configured to increase the output power of the turbine, at least in part, by directing a water flow to and away from the turbine and inducing a shaped flow separation region around the trailing edge of the duct assembly. [0021] Referring to Figure 1, a ducted turbine module is generally shown as item

100. The module 100 generally comprises a cross-flow turbine 1 10, a generator 120, and a duct assembly 130.

[0022] The cross-flow turbine 110 comprises a plurality of elongated blades 114 coupled to a central shaft 112 by a plurality of arms 116. The turbine 110 is rotatably coupled to the duct assembly 130 as further described below. The turbine 110 may be any cross- flow turbine known in the art, such as, for example, a straight bladed vertical axis turbine (such as those available from Edinburg Designs), a helical blade turbine (such as those available from Lucid Technologies), or any variation thereof, including a drag driven cross-flow turbine (Neptune Renewable Energy).

[0023] The generator 120 is in driving engagement with the shaft 112 of the turbine 110 such that rotation of the shaft 112 drives the generator 120 to produce power. The generator 120 may be any generator known in the art, such as, for example, a permanent magnet direct drive generator (such as those available from Alxion). In the present embodiment, the generator 120 is mounted to the top of a cylindrical tube 122 that is mounted to the top of the duct assembly 130. The shaft 112 of the turbine 1 10 extends through the tube 122 and couples to the generator 120. In the alternative, the generator can be directly mounted to the top of the duct assembly 130. In the further alternative, a gearbox (not shown) can be connected between the generator 120 and the turbine 110 to increase the rotations per minute of the generator 120. In the further alternative, the generator 120 may be replaced with a pump, such as, for example, a variable speed direct-drive hydraulic pump. Water may be pumped into a reservoir as a form of energy storage that can be subsequently converted into electricity using a Kaplan turbine. In the alternative, the hydraulic pump may be connected to hydraulic motors to produce electricity.

[0024] The duct assembly 130 functions to direct water flow to and away from the turbine 1 10 and induce a shaped flow separation region around the trailing edge of the duct assembly 130 to increase the output power of the turbine 110. The duct assembly 130 generally comprises two oppositely facing ducts 132 and a support assembly 140. [0025] The support assembly 140 functions to position and orient the ducts 132 with respect to the turbine 1 10 and with respect to each other as further described below. In the present embodiment, the support assembly 140 comprises an upper plate 142 and a lower plate 144. The upper plate 142 is a rectangular plate that is fixed to the top of each duct 132 and the lower plate 144 is a rectangular plate that is fixed to the bottom of each duct 132. Each plate 142, 144 comprises a central bore 143, 145 therethrough, with built- in bearings, for rotatably mounting the turbine 110 within the duct assembly 130 between the ducts 132. The shaft 112 of turbine 1 10 extends through the bore 143 of the upper plate 142 and the cylindrical tube 122 and couples to the generator 120. In the alternative, the turbine 110 may be decoupled from the support assembly 140 and supported by a separate structure. In the further alternative, the support assembly 140 may comprise a single upper or lower plate 142, 144. In the further alternative, the support assembly 140 may comprise alternative shapes and support structures that position and orient the ducts 132 with respect to the turbine 1 10 and each other, for example, Figure 2 depicts a duct assembly 200 comprising a support assembly 240 having an hourglass shaped top and bottom plates 242, 244 with a narrow center section extending between the ducts 232. In the further alternative, the support assembly 140 may position and orient each duct 132 independently without any interconnection between the ducts 132.

[0026] Referring to Figure 3, a cross-sectional plan view of the duct assembly

130 depicts the cross-sectional shape and relative position and orientation of the ducts 132. The ducts 132 comprise identical cross-sections that are oppositely facing and symmetrical about a plane 312 that is coplanar with the rotational axis 300 of the turbine 1 10. The symmetrical shape of the ducts 132 permits the ducted turbine module 100 to operate in bidirectional water flows. Each duct 132 further comprises an active surface 134 that faces towards the turbine 1 10 and a back surface 136 that faces away from the turbine 1 10. The active surface 134 comprises a generally convex streamlined shape that is fixed to the back surface 136 and protrudes away from the back surface 136 at an angle of attack 310. In the present embodiment, the back surface 136 comprises a generally planar shape. In the alternative, the back surface 136 may comprise non-planar shapes, for example, Figure 4 depicts a duct assembly 430 wherein the back surface 436 of the ducts 432 comprises a generally concave shape that curves into the duct 432.

[0027] Referring again to Figure 3, each duct has a width 306, measured in a direction parallel to the plane 312 and orthogonal to the rotational axis of the turbine 1 10, and a length 308, measured in a direction orthogonal to the plane 312. The ducts 132 are positioned outside of the rotational diameter 302 of the turbine 110 defining a frontal width 304 of the duct assembly 130 measured in a direction parallel to the plane 312 and orthogonal to the rotational axis 300 of the turbine 1 10.

[0028] Referring to Figure 5, the ducts 132 may be comprised of generally hollow bodies constructed of a plurality of stiffeners 500 and webs 502 to which the active surface 134 and rear surface 136 are affixed. The stiffeners 500 and webs 502 function to provide additional structural support to the ducts 132. In the alternative, the ducts 132 may be constructed of solid piece of material, such as, for example, a concrete shell infused with foam.

[0029] While not being bound by theory, it is believed that the output power of the turbine 1 10 can be increased, at least in part, by directing a water flow to and away from the turbine 1 10 and inducing a shaped flow separation region around the trailing edge of the duct assembly 130. Referring to Figure 6, it is believed that a duct assembly 130 having a particular range of frontal widths 304, and ducts 132 having particular ranges of widths 306, lengths 308 and angles of attack 310, can produce a shaped flow separation region 600 around the trailing edge of the duct assembly 130 that virtually extends the downstream length of the ducts 132, thereby confining the water flow exiting the duct assembly 130 and concentrating more flow through the downstream portion of the turbine 1 10. This has the effect of both increasing power output, since more power is produced by downstream blades of the turbine 1 10, and decreasing fluctuations in turbine torque that are caused by an uneven amount of torque produced by the upstream blade as compared to the downstream blade 1 14. The separation region 600 also creates a low pressure region behind the turbine 1 10. Since flow is governed by a difference in pressure, the low pressure behind the turbine 1 10 acts to draw more mass flow through the turbine 1 10.

[0030] It is believed that the shaped flow separation region 600 is created due to the sharp trailing edge of the ducts 132. The flow passing through the turbine 1 10 cannot stay attached to the ducts 132 (due to high adverse pressure gradient) and therefore separates and creates the separation region 600. It is believed that the shaped flow separation region 600 may be created by a duct assembly 130 having a frontal width 304 of between 1.75 to 2.25 times the rotational diameter 302 of the turbine 110, and ducts 132 having a width 306 of between 0.35 to 0.6 times the rotational diameter 302 of the turbine 110, a length 308 of between 0.9 to 1.3 times the rotational diameter 302 of the turbine 110, and an angle of attack 310 of between 60 to 80 degrees. In the alternative, the frontal width 304 of the duct assembly 130 may be between 1.8 to 2.2, 1.85 to 2.15, 1.9 to 2.1 , 1.95 to 2.05, or 2 times the rotational diameter 302 of the turbine 1 10. In the further alternative, the ducts 132 may have a width 306 of between 0.4 to 0.55, 0.42 to 0.48, or 0.44 times the rotational diameter 202 of the turbine 1 10. In the further alternative, the ducts 132 may have a length 308 of between 0.95 to 1.2, 0.975 to 1.1, or 1 times the rotational diameter 202 of the turbine 1 10. In the further alternative, the ducts 132 may have an angle of attack 310 of between 65 to 75, 67.5 to 72.5, or 70 degrees.

[0031] The ducted turbine module 100 may be deployed in a water flow by mounting the module 100 to a floating platform 700 as shown in Figure 7, tethering the module 100 to a gravity base 800 as shown in Figure 8, mounting the module 100 to a gravity base 900 as shown in Figure 9; or any other manner apparent to a person skilled in the art. In addition, the module 100 may be vertically stacked in an array 1000 of modules 100 as shown in Figure 10, horizontally stacked in an array 1 100 of modules 100 as shown in Figure 11 , horizontally spaced in a side-by-side configuration 1200 as shown in Figure 12, or in any other arrangement of modules apparent to a person skilled in the art.

[0032] Example [0033] In one example, the performance of the module 100 was assessed using computational fluid dynamics simulations for a variety of duct assemblies. Referring to Figure 13, five duct assemblies 1300, 1320, 1340, 1360, and 1380 were assessed having the configurations specified in Table 1 with the rotational diameter of the turbine of 36 inches. The widths, lengths and frontal widths in Table 1 are expressed as a multiple of the rotational diameter of the turbine, while the angle of attack is expressed in degrees.

Table 1

[0034] Each duct assembly 1300, 1320, 1340, 1360, and 1380 was subjected to a

Computational Fluid Dynamics (CFD) simulation using STAR CCM+, a commercial CFD code. The simulations were run on a PC and validated using experimental testing. The turbine performance was modeled using a Reynolds Averaged Navier Stokes (RANS) Solver and a k-epsilon turbulence model. The CFD modeling approach was extensively validated based on experimental data. The results of the simulations were then assessed for: average torque produced by the turbine over one revolution, output power of the turbine divided by the total frontal area of the ducted turbine module (C_k), torque ripple factor (TRF) (defined as the maximum torque divided by the average torque over a revolution), and area ratio defined as the total frontal area of the ducted turbine module divided by the turbine swept area. The resultant measurements for each duct assembly 1300, 1320, 1340, 1360, and 1380 are shown in Table 2. Table 2

[0035] Table 2 demonstrates that in this example, the best C_k value was produced by duct assembly 1320 having a duct width of 0.44 times the rotational diameter of the turbine, a duct length of 1.00 times the rotational diameter of the turbine, and a frontal width of 2.00 times the rotational diameter of the turbine. Table 2 also demonstrates that in this example: duct assemblies having duct widths 50% less or 50% more than 0.44 times the rotational diameter of the turbine provided C_k values worse than duct assembly 1320; duct assemblies having duct lengths 46% more than 1.00 times the rotational diameter of the turbine provided C_k values worse than duct assembly 1320; duct assemblies having frontal widths 22% less or 22% more than 2.00 times the rotational diameter of the turbine provided C_k values worse than duct assembly 1320.

[0036] While the present invention is illustrated by description of several embodiments and while the illustrative embodiments are described in detail, it is not the intention of the applicants to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications within the scope of the appended claims will readily appear to those sufficed in the art. The invention in its broader aspects is therefore not limited to the specific details, representative apparatus and methods, and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of the general concept.

Claims

Claims:

1. A duct assembly for a cross-flow water turbine, the duct assembly comprising:

(a) two oppositely facing symmetrical ducts, each duct comprising an active surface and a back surface, the active surface facing the turbine and protruding away from the back surface, the active surface symmetrical about a plane coplanar with the rotational axis of the turbine, the active surface having an angle of attack at the leading and trailing edges of between 60 and 80 degrees, each duct having a length of between 0.9 to 1.3 times the rotational diameter of the turbine and a width of between 0.35 to 0.6 times the rotational diameter of the turbine; and

2. The duct assembly as claimed in claim 1, wherein the frontal width of the duct assembly is between 1.8 to 2.2 times the rotational diameter of the turbine.

3. The duct assembly as claimed in claim 1, wherein the frontal width of the duct assembly is between 1.85 to 2.15 times the rotational diameter of the turbine.

4. The duct assembly as claimed in claim 1, wherein the frontal width of the duct assembly is between 1.9 to 2.1 times the rotational diameter of the turbine.

5. The duct assembly as claimed in claim 1 , wherein the frontal width of the duct assembly is between 1.95 to 2.05 times the rotational diameter of the turbine.

6. The duct assembly as claimed in claim 1, wherein the frontal width of the duct assembly is 2 times the rotational diameter of the turbine.

7. The duct assembly as claimed in any of claims 1 to 6, wherein each duct has a width of between 0.4 to 0.55 times the rotational diameter of the turbine.

8. The duct assembly as claimed in any of claims 1 to 6, wherein each duct has a width of between 0.42 to 0.48 times the rotational diameter of the turbine.

9. The duct assembly as claimed in any of claims 1 to 6, wherein each duct has a width of 0.44 times the rotational diameter of the turbine.

10. The duct assembly as claimed in any of claims 1 to 9, wherein each duct has a length of between 0.95 to 1.2 times the rotational diameter of the turbine.

11. The duct assembly as claimed in any of claims 1 to 9, wherein each duct has a length of between 0.975 to 1.1 times the rotational diameter of the turbine.

12. The duct assembly as claimed in any of claims 1 to 9, wherein each duct has a length of 1 times the rotational diameter of the turbine.

13. The duct assembly as claimed in any of claims 1 to 12, wherein the active surface of each duct has an angle of attack at the leading and trailing edges of between 65 to 75 degrees.

14. The duct assembly as claimed in any of claims 1 to 12, wherein the active surface of each duct has an angle of attack at the leading and trailing edges of between 67.5 to 72.5 degrees.

The duct assembly as claimed in any of claims 1 to 12, wherein the active surface of each duct has an angle of attack at the leading and trailing edges of 70 degrees.