BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to hydroelectric turbine or pump installations with a radial flow runner of the Francis type.
2. Description of the Related Art
Hydraulic machines including a radial flow runner of the Francis type are suffering from axial thrust applied to the runner of the hydraulic machine. Since the sealing between the runner and the high pressure side of the water passage cannot be made perfectly tight, water can get in the space between the head cover of the hydraulic machine and the runner crown resulting in a high axial thrust. To reduce the axial thrust prior art has proposed several concepts. One concept comprises balancing pipes draining the water passing the seals to the low pressure side of the water passage (see e.g. U.S. Pat. No. 1,820,150 to Moody). Another concept comprises balance holes within the runner crown leading to the runner hub or to the space between the blades of the runner (see e.g. U.S. Pat. No. 4,086,020 to Seiichi and Syoji). Balancing pipes are generally expensive. The effectiveness of the prior art balancing holes depends on the revolution speed of the runner and the blade geometry and therefore leading not always to satisfactory results concerning thrust reduction. Especially in the case of modernization projects when an existing runner relying on balancing holes has to be replaced by a new runner the situation can occur that the modern blade geometry cannot be accommodated by balancing holes of the known type and the installation of balancing pipes is impractical since the existing hydraulic machine is embedded in concrete. It is desirable in many modernization projects to have new runners with blades which extend closer to the axis of rotation at the trailing edge near runner crown. This geometry provides improved performance characteristics but in many cases makes the use of balancing holes in the runner crown less effective at reducing thrust due to radial pumping effects within the runner crown space below the shaft flange. In some cases where the flange connecting the runner to the shaft is at a relatively low elevation, there may no longer be sufficient space available in the runner crown flange to accommodate balancing holes of the known type and so an alternative solution for thrust reduction is necessary.
What is needed in the art is an alternative concept for reducing the axial thrust being less expensive than balancing pipes and easily applicable within modernization projects.
SUMMARY OF THE INVENTION
The present invention provides a runner of the Francis type for a hydraulic turbine or pump. The runner has a low pressure side and a high pressure side. The runner also has a crown including a seal for sealing a space above the crown against water from the high pressure side, a plurality of blades, and each blade of the plurality of blades being defined by a pressure surface, an oppositely facing suction surface, an edge adjoining the high pressure side of the runner, and a spaced apart edge adjoining the low pressure side of the runner. The runner further includes at least one passage being capable to drain high pressure leakage water passing the seal to the low pressure side. The at least one passage includes an inlet aperture located in a portion of the crown which during operation is exposed to high pressure leakage water. The at least one passage is located within a respective blade of the plurality of blades and leads from the inlet aperture to the edge adjoining to the low pressure side of the same respective blade. The passage is shaped to form a continuous opening in the edge adjoining to the low pressure side.
The axial thrust can be reduced by a runner that includes at least one passage leading from the runner crown to the trailing edge of at least one of the runner blades. Having leakage water exiting the trailing edge may reduce drag forces as the runner rotates and result in an improvement in hydraulic efficiency.
BRIEF DESCRIPTION OF THE DRAWINGS
The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein:
FIG. 1 is a cross-sectional view of a Francis turbine runner according to the present invention;
FIG. 2 is a cross-sectional view of a runner blade according to an embodiment of the present invention;
FIG. 3A shows a cross-sectional view of the runner blade of FIG. 2, taken across line 3A-3A;
FIG. 3B shows different kinds of embodiments of a cross-section view of the runner blade of FIG. 2, taken across line 3B-3B;
FIG. 4 is a cross-sectional view of a runner blade according to another embodiment of the present invention;
FIG. 5 shows a cross-sectional view of the runner blade according to FIG. 4, taken across line 5-5; and
FIG. 6 is a cross-sectional view of a runner blade according to another embodiment of the present invention.
Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate embodiments of the invention and such exemplifications are not to be construed as limiting the scope of the invention in any manner.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 displays schematically a cross-sectional view of a Francis turbine runner according to the present invention. The runner crown is designated as 11. A runner blade 2 extends between the crown 11 and the band designated as 12. The blade 2 has two edges designate by 3 and 4. The fluid entering the runner flows from edge 3 towards edge 4, whereas the high pressure side adjoins to edge 3 and the low pressure side adjoins to edge 4. It is clear that in pumping mode the flow direction of the fluid is reversed. The runner crown 11 includes circumferential located seal 13 designated as 13. Seal 13 are construed to seal the space above crown 11 against high pressure water. However due to the imperfection of the sealing a small amount of high pressure water will be present in the space above the runner crown 11 leading to the undesired axial thrust. The runner crown 11 includes an inlet aperture designated by 6. The inlet aperture 6 is located in a portion of the crown, which is exposed to high pressure water passing the seal 13. The blade 2 comprises a passage designated by 5. The passage 5 leads from inlet aperture 6 to a portion of edge 4 adjoining the low pressure side where the passage 5 forms an opening which is designated by 7. The axial thrust is relieved by draining the leakage water from the space above crown 11 directly through the passage 5 inside blade 2 to the low pressure side. Since opening 7 is located in the edge 4 directly adjoining the low pressure side the thrust is relieved to a high degree. In a preferred embodiment of the invention, the location of the opening 7 is at an equal or larger radial distance from the axis of rotation than the inlet aperture 6. This avoids backpressure due to the radial pumping effect of rotation. Therefore the runner according to the invention relieves the thrust to lower values compared with the runner of U.S. Pat. No. 4,086,020 because the balancing holes of U.S. Pat. No. 4,086,020 leading to the hub and the space between the blades do not adjoin directly to the low pressure side of the runner. The radial pumping effect within the hub of U.S. Pat. No. 4,086,020 is significant and results in higher pressure above the runner and consequently higher axial downthrust.
FIG. 2 displays schematically a cross-sectional view of a runner blade according to present invention. The blade is designated as 2. The blade 2 has an edge 3 adjoining the high pressure side and an edge 4 adjoining the low pressure side. 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 blade 2 shown in FIG. 2 contains a passage which is designated as 5. The blade 2 has an inlet apertures designated as 6. At the edge 4, there is a continuous opening designated as 7. The continuous opening 7 extends preferably over at least 15% of the developed length of the edge 4 (x/L>=0.15). The extension of the continuous opening 7 over a relatively large area of the edge 4 ensures that the leakage high pressure water can pass easily to the low pressure side for a wide range of revolution numbers leading to a low axial thrust for all operation modes. Inlet aperture 6, passage 5 and the continuous opening 7 are forming a smooth passage through the blade minimizing losses as the leakage water flows through the blade.
FIGS. 3A-3B display schematically cross-sectional views through the blade 2 of FIG. 2 along the marked sections 3A-3A and 3B-3B. FIG. 3B-3B displays three different embodiments of the continuous opening 7 which is displayed in three different views along section 3B-3B. In the view along section 3A-3A it can be seen that the blade 2 comprises a base part which is designated by 8 and a cover part which is designated by 9. The base part 8 includes either the entire suction side or pressure side surface of the blade as well as the entire surface of the edge adjoining the high pressure side and a substantial portion of the surface of the edge adjoining the low pressure side. A cavity is machined or cast into the base part 8. The thinner cover part 9 is attached to the base part 8 thus forming the gas passage 5. The cover part 9 may be metal or composite material, may be cast formed or machined and may be attached by welding or by a bonding material (epoxy, glue, etc.). The topmost cross-sectional view along section 3B-3B shows a first embodiment of the continuous opening 7. The continuous opening 7 is confined by the pressure and suction side surfaces which meet at the trailing edge 4. In this first embodiment the pressure and suction side surfaces are ending respectively at the same distance measured from the edge 3 adjoining the high pressure side along the section's camberline. The middle cross-sectional view along section 3B-3B shows a second embodiment of the continuous opening 7. In this second embodiment the pressure side surface extends further than the suction side surface measured from the edge 3 adjoining the high pressure side along the section's camberline. The bottom cross-sectional view along section 3B-3B shows a third embodiment of the continuous opening 7. In the third embodiment the edge 4 adjoining the low pressure side in the region of opening 7 is profiled to minimize vortex shedding. Of course this kind of profile can be present over the whole length of edge 4.
FIG. 4 displays schematically a cross-sectional view of a runner blade according to present invention in another embodiment. Additionally to the blade of FIG. 2 the embodiment according FIG. 4 includes three spacer pieces one of them being designated as 10.
FIG. 5 shows a cross-sectional view along cross-section 5-5 displaying a side view of the spacer piece 10. Spacer pieces 10 are positioned within the passage 5 as needed to avoid the buckling of the cover part 9. The spacer pieces 10 could be integral to the base part 8 or fixedly attached to either the base part 8 or cover part 9. It is clear that the number of spacer pieces 10 is not restricted to the number of three but there can be any number of spacer pieces 10.
The spacer pieces 10 may form an obstacle to the leakage water flow. Therefore it may be favorable that the spacer pieces are of aerodynamic shape. FIG. 6 shows the runner according to the present invention featuring aerodynamically shaped spacer pieces 10.
It is clear that the embodiments shown in the figures are examples of a much broader variety of embodiments each employing the inventive ideas. For example there could be several separate passages through one blade leading from separate inlet apertures to several separate continuous openings located at different portions of the edge adjoining the low pressure side. The different passages could also be located in different blades.
While this invention has been described with respect to at least one embodiment, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.
Patent Application
20190345953
