WO2022171336A1

WO2022171336A1 - Runner for a hydraulic turbine or pump

Info

Publication number: WO2022171336A1
Application number: PCT/EP2021/085817
Authority: WO
Inventors: Stuart Coulson; Steven MC HALE; Jesse ZOLL; Richard Reese; Jason FOUST; Brandon HARMER
Original assignee: Voith Patent Gmbh
Priority date: 2021-02-11
Filing date: 2021-12-15
Publication date: 2022-08-18

Abstract

A runner for a hydraulic turbine or pump, having an outlet diameter D and comprising a plurality of blades (2), each blade comprising a leading edge (3) and a spaced apart trailing edge (4), at least one of the blades having means for supplying a flow of oxygen containing gas to the trailing edge of the same blade whereas the means comprise a gas inlet aperture (6), a gas passage (5) and one or more openings (7), wherein the at least one of the blades comprises one or more protrusions (12), whereas the one or more protrusion is spaced apart from the trailing edge in a direction perpendicular to the trailing edge by less than 1% of the outlet diameter D, and whereas the one or more protrusion intersects with at least one of the one or more openings.

Description

Runner for a hydraulic turbine or pump

The present invention relates generally to hydroelectric turbine or pump installations. More particularly, this invention pertains to hydroelectric installations with means for enhancing the level of dissolved gas in water passing through the turbine or pump.

A significant environmental problem for many hydroelectric facilities is the water quality of discharges. Various attempts have been made to enhance the level of dissolved oxygen in discharged water of hydroelectric installations. For example, U.S. Pat. No. 5,924,842 to Beyer, James R. discloses a runner for a Francis turbine comprising a crown; a band substantially concentric with the crown; and a plurality of blades extending between crown and the band at spaced intervals along the crown, each blade fixedly secured to the crown at an inner edge and to the band at a distal outer edge, each blade having a water directing surface defined by a pressure side, an opposite facing suction side, a leading edge and a spaced apart trailing edge, at least one of the blades including: a leading edge blade portion having a rear edge in which a first slot is machined along at least a portion of the rear edge; a trailing portion having a front edge in which a second slot is machined along at least a portion of the front edge; wherein the trailing portion is fixedly secured to the leading blade portion along the front edge and the rear edge, respectively, so that the first and second channels cooperate to form an integral passage in the at least one of the blades; and means for discharging an oxygen containing gas from the integral passage to a location adjacent the trailing edge.

The objective of the mentioned state of the art is to increase the level of dissolved oxygen downstream of the turbine or pump by introducing an oxygen containing gas into the water passing through the unit. The amount of gas introduced into the water passing through the unit depends on the pressure conditions on the low-pressure side of the runner. For example when the tailwater level rises and therefore the backpressure is increased, the aeration capability of the prior art designs may become ineffective. It is common at hydropower plants that the downstream level (often referred to as tail water level) rises as more flow is passed through the turbine(s) of the hydro plant or if flow is released over an adjacent spillway. The resulting higher tail water level increases the pressure at the outlet of the turbine. In aerating turbines, the source of the oxygen containing gas is often atmospheric air in the hydro plant. As the pressure downstream of the turbine runner increases, the flow of atmospheric air is reduced or even stopped due to insufficient pressure differential.

WO 2019/179742 A1 describes a runner of a hydroelectric turbine or pump with improved level of dissolved oxygen when backpressure increases. This is achieved by altering the geometry near the trailing edge of the runner to create a local drop in pressure on the trailing edge surface. The described runner comprises openings in the trailing edge surface to admit gas to the passing fluid during operation of the runner. The profile of the suctions side surface at the location of the openings is concave.

The inventors have realized that such a profile has a negative impact on the performance of the runner.

The objective of the present invention is to specify a runner of a hydroelectric turbine or pump featuring an equal or better behavior concerning dissolved oxygen in backpressure situation having a less significant impact on performance of the runner.

The problem is solved by a runner according to the independent claim. Other favorable implementations of the invention are disclosed in the depended claims.

The invention will hereinafter be described in conjunction with the appended drawings:

Fig. 1 is a cross-sectional view of an axial type runner;

Fig. 2 is a cross-sectional view of a Francis type runner;

Fig. 3 shows a blade with means for supplying a flow of oxygen containing gas; Fig. 4 shows a blade with means for supplying a flow of oxygen containing gas; Fig. 5 shows a protrusion;

Fig. 6 shows different types of protrusions;

Fig. 7 shows a protrusion directly located at the trailing edge; Fig. 8 shows a protrusion spaced apart from the trailing edge;

Fig. 9 shows different profiles of protrusions in y-direction;

Fig. 10 shows the outlet diameter D for different runner types;

Fig. 11 shows the intersection of a protrusion with an opening; Fig. 12 shows different arrangements of protrusions and openings;

Fig. 13 shows different arrangements of protrusions on a wide opening.

Figure 1 displays schematically a cross-sectional view of an axial type runner. The runner hub is designated as 1. A runner blade designated as 2 extends from the hub 1. The fluid flow is divided by the blade 2 whereas one side of the blade 2 forms the pressure surface and the other side the suction surface. The pressure side surface is designated by 10 and the suction side surface is designated by 11.

Figure 2 displays schematically a cross-sectional view of a Francis type runner (only the right side is shown completely). The runner crown is designated as 8. A runner blade extends between the crown 8 and the band designated as 9. The blade has a leading edge designated as 3 and a trailing edge designated as 4 meaning that the fluid entering the runner flows from the leading edge 3 towards the trailing edge 4. Blades 2 of any type of runner are characterized by leading edge 3, trailing edge 4, pressure side surface 10 and suction side surface 11. Each runner comprised a plurality of blades 2. At least one of the blades 2 comprises means for supplying a flow of oxygen containing gas to the trailing edge 4of the same blade 2. Figure 3 displays a blade comprising means for supplying a flow of oxygen containing gas to the trailing edge 4. The means comprise a gas inlet aperture designated as 6, a gas passage designated as 5 and one or more openings in the trailing edge surface 4 to admit gas out of the gas passage 5 to the passing fluid during operation of the runner. The blade shown in figure 3 comprises one single opening designated by 7. Figure 4 displays a blade comprising means for supplying a flow of oxygen containing gas to the trailing edge 4 in another embodiment. The blade comprises a plurality of openings. One of the openings is designated by 7. It is also possible that a blade comprises more than one separate gas passages 5. In this case each gas passage 5 has its own separate gas inlet aperture 6 and its own opening or openings 7.

The inventors have realized that the protrusions of the blade on or near the trailing edge are able to increase the level of dissolved oxygen and having at the same time a smaller impact on performance of the runner.

Figure 5 illustrates what is meant by the term protrusion. The upper part of figure 5 shows a curve Z as a function of the variable x. The variable x describes the arc length of a curve running along the trailing edge or in parallel to the trailing edge. Z(x) is the thickness of the blade at the location denoted by x. It is clear that a protrusion is a local thickening of the blade. The dashed lines indicate the borders of the protrusion. The distance between the dashed lines is the extension of the protrusion along x. The extension of the protrusion is designated by L. The lower part of figure 5 shows the slope dZ(x)/dx of Z(x). In x-direction the protrusion starts with an inclining flank which is reflected by the slope being positive, than follows a plateau where slope is zero and finally a declining flank where the slope is negative. The profile of the protrusion shown in figure 5 is just an example. The profiles of protrusions can vary in a wide range which is illustrated in the following figures. For example there does not have to be a plateau and the profile can have kinks - that is the profile does not have to be smooth. Also the thickness of blade could vary along x slowly by a small additional slope compared to the slopes shown in figure 5. That means that the baseline of the curve of the lower part of figure 5 could deviate from zero by a small amount in positive or negative direction. In any case within a protrusion the blade thickness Z(x) assumes at least at one of the borders a minimum value denoted by Z_min and between the borders a maximal value denoted by Zmax. The quotient Zmax/Zmin is a measure of the amount of the local thickening of the blade by the protrusion. Figure 6 shows different embodiments of a protrusion. The left part of figure 6 shows a protrusion which is established by corresponding profiles of the pressure side surface 10 and of the suction side surface 11 of the blade. The profiles on the both sides don’t have to be symmetrical. The right part of figure 6 shows the two limiting cases. On the upper part the protrusion is established by a corresponding profile on the pressure side surface 10 alone whereas the suction side profile is more or less flat in the region of the protrusion. On the lower part the protrusion is established by a corresponding profile on the suction side surface 11 alone whereas the pressure side profile is more or less flat in the region of the protrusion. The inventors have realized that the embodiment according to the lower right part of figure 6 is especially advantageous since in this embodiment the impact on runner performance is smaller than in the other embodiments.

Figure 7 shows a protrusion designated by 12 which is located directly at the trailing edge 4 of a blade. In this case x runs along the trailing edge 4 as is indicated by the dashed arrowed line. The extension of the protrusion 12 in the direction perpendicular to the trailing edge is designated by the letter W.

Figure 8 shows a protrusion 12 which is not located directly at the trailing edge 4 of a blade but spaced apart by a distance which is designated by the letter Y. In this case x runs along a curve which is spaced apart from the trailing edge 4 by Y as is indicated by the dashed arrowed line.

Figure 9 shows different profiles of protrusions regarded in a direction perpendicular to the trailing edge. This direction is indicated by the arrows designated by y. The left side shows protrusions which are located directly at the trailing edge whereas the right side shows protrusions spaced apart from the trailing edge by the distance Y. The top part of the figure shows straight profiles, the middle part shows convex profiles and the bottom part shows concave profiles. The other sides of the blade could of course be optionally profiled accordingly. The inventors have realized that the local character of the protrusions leads to a small or even neglectable impact on runner performance. For this reason it is advantageous when the extension L of the protrusions is smaller or equal to 10% of the developed length of the trailing edge. To avoid cavitation on the surface of the protrusions it is further advantageous when the quotient Zmax/Zmin is smaller or equal to 2.0. It is further advantageous when the extension W in the direction perpendicular to the trailing edge is smaller than 5% of the outlet diameter of the runner and when the distance Y of the protrusion from the trailing edge is smaller than 1 % of the outlet diameter of the runner. The latter condition is obviously met in case that the protrusion is located directly at the trailing edge.

Figure 10 shows the outlet diameter D of a Francis type runner (top part) and an axial flow runner (lower part).

To establish the positive effect of a protrusion on the level of dissolved oxygen it is necessary that the protrusion 12 intersects with an opening 7. The phrase ‘intersect’ means that the extension of the protrusion 12 in x-direction has an overlap with the extension of the opening 7 in x-direction. In case that the protrusion is spaced apart from the trailing edge the condition of intersection is given, when the projection of the protrusion onto the trailing edge intersects with an opening. A limiting case of this condition is shown in figure 11. The right side border of the protrusion 12 coincides with the left side border of the opening 7. The mentioned borders are indicated by the dashed line. The other limiting case can be obviously obtained by mirroring figure 11 on the dashed line.

Figure 12 shows different arrangements of protrusions and openings. The left side of the figure shows protrusions having a rounded profile whereas the left side shows protrusions having a roof shaped profile. The lines (a) and (b) show arrangements where each protrusion is centered on the center of a corresponding opening. In line (c) the protrusions are located between the openings. In line (d) the arrangement is a combination of (a) and (c). The protrusion can be integral to the blade body as shown in lines (a), (c) and (d) or connected to the blade body by gluing or welding or other connection means as indicated in line (b). It has to be noted that in the lines (c) and (d) protrusions intersect with more than one opening. Also has to be noted that line (c) shows arrangements where two protrusions intersect with one and the same opening. Figure 13 shows different arrangements of protrusions in relation to a wide opening in a similar manner as in figure 12. In line (a) and (b) three protrusions are distributed equally spaced along the extension of the opening. The first and last of the protrusions extent outside the borders of the opening. In line (c) two protrusions are located completely within the borders of the opening. In line (d) the arrangement is a combination of (a) and (c). It has to be noted that in the embodiments of figure 13 two or more protrusions intersect with one and the same single opening. The inventors have realized that such an arrangement with several smaller protrusions intersecting with a wider opening has a very small impact on runner performance. It is further advantageous that in such an arrangement the space between two adjacent protrusions is equal or smaller than the extension L of both of the two adjacent protrusions.

The current patent application is also related to a method of refurbishing an existing runner wherein the runner is provided with protrusions according to the preceding paragraphs. The method comprises a step of connecting one or more protrusions to the at least one blade of the runner.

List of references

1 Hub

2 Blade 3 Leading edge

4 Trailing edge

5 Gas passage

6 Inlet aperture

7 Opening 8 Crown

9 Band

10 Pressure side surface

11 Suction side surface

12 Protrusion

Claims

1. A runner for a hydraulic turbine or pump, having an outlet diameter D and comprising a plurality of blades (2), each blade (2) being defined by a pressure surface (10), an oppositely facing suction surface (11), a leading edge (3) and a spaced apart trailing edge (4), at least one of the blades (2) having means for supplying a flow of oxygen containing gas to the trailing edge (4) of the same blade (2) whereas the means comprise a gas inlet aperture (6), a gas passage (5) and one or more openings (7) in the trailing edge surface (4) to admit gas out of the gas passage (5) to the passing fluid during operation of the runner, characterized in that the at least one of the blades (2) comprises one or more protrusions (12), whereas the one or more protrusion (12) is spaced apart from the trailing edge (4) of the same blade (2) in a direction perpendicular to the trailing edge by less than 1 % of the outlet diameter D, and whereas the one or more protrusion (12) intersects with at least one of the one or more openings (7).

2. A runner for a hydraulic turbine or pump according to claim 1 , wherein the at least one of the blades (2) comprises more than one protrusion (12), whereas at least two of the protrusions (12) intersect with one and the same opening (7) of the one or more openings (7).

3. A runner for a hydraulic turbine or pump according to claim 1 or 2, wherein an extension L of the one or more protrusion (12) along x is smaller or equal to 10% of a developed length of the trailing edge (4) of said blade (2), and wherein x is the arc length of a curve running along the trailing edge (4) or in parallel to the trailing edge (4).

4. A runner for a hydraulic turbine or pump according to claim 2 and 3, wherein the space between two adjacent protrusions (12) intersecting with one and the same opening (7) is equal or smaller than the extension L of both of the two adjacent protrusions (12).

5. A runner for a hydraulic turbine or pump according to one of the preceding claims, wherein a quotient Z_max/Z_min is smaller or equal to 2.0, and wherein Z_max is the maximal value of the blade thickness and Z_min is the minimal value of the blade thickness at the one or more protrusion (12).

6. A runner for a hydraulic turbine or pump according to one of the preceding claims, wherein an extension of the one or more protrusion (12) in the direction perpendicular to the trailing edge (4) W is smaller than 5% of the outlet diameter D of the runner.

7. A runner for a hydraulic turbine or pump according to one of the preceding claims, wherein the one or more protrusion (12) is established by a corresponding profile on the suction side surface (11) alone.

8. A runner for a hydraulic turbine or pump according to one of the preceding claims, wherein the one or more protrusion (12) is integral to said blade (2).

9. A runner for a hydraulic turbine or pump according to one of claims 1 to 7, wherein the one or more protrusion (12) is connected to said blade (2).

10. A method of refurbishing an existing runner of a hydraulic turbine or pump, wherein the runner has an outlet diameter D and comprises a plurality of blades (2), each blade (2) being defined by a pressure surface (10), an oppositely facing suction surface (11), a leading edge (3) and a spaced apart trailing edge (4), at least one of the blades (2) having means for supplying a flow of oxygen containing gas to the trailing edge (4) of the same blade (2) whereas the means comprise a gas inlet aperture (6), a gas passage (5) and one or more openings (7) in the trailing edge surface (4) to admit gas out of the gas passage (5) to the passing fluid during operation of the runner, characterized in that the method comprises a step of connecting one or more protrusions (12) to the at least one blade (2) of the runner in a way to establish, that the one or more protrusion (12) is spaced apart from the trailing edge in a direction perpendicular to the trailing edge by less than 1 % of the outlet diameter D, and that the one or more protrusion (12) intersects with at least one of the one or more openings (7).