The present invention relates generally to hydroelectric turbine or pump installations comprising a radial flow runner of the Francis type.
The objective of the present invention is to improve the known hydraulic machine concerning efficiency, vibration and noise behavior in the partial load regime.
It is known, that by adding air to the water flowing through the runner of the radial flow type, the efficiency in the partial load regime can be materially enhanced (see e.g. U.S. Pat. No. 1,823,624 to Nagler). In practice, it turns out that for adding air a compressor is needed. The compressor consumes power and partially or completely negates the benefit of reducing friction losses. The objective of the present invention is to disclose a layout of a hydraulic machine where no compressor or at least a compressor consuming less power compared to the state of the art is needed for air admission.
This objective is achieved by a hydraulic machine according to claim 1. Other favorable implementations of the invention are disclosed in the depended claims.
The inventors have recognized that this objective can be achieved by a runner comprising at least one passage leading from the runner crown to the runner band whereas the passage is located within one of the runner blades and an air admission opening positioned in the head cover above the runner.
The invention will hereinafter be described in conjunction with the appended drawings:
A runner blade 2 extends between the crown 11 and the band designated as 12. The blade 2 has two edges designated 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 comprises circumferential located sealing means designated as 13. Sealing means 13 are construed to seal the space between head cover 1 and crown 11 against high pressure water. However due to the imperfection of the sealing a amount of high pressure water will be present in the space above the runner crown 11. The runner crown 11 comprises 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 sealing means 13. The blade 2 comprises a passage designated by 5. The passage 5 leads from inlet aperture 6 to the band 12 where the passage 5 forms an opening which is designated by 7. The high pressure in the chamber 15 above the runner crown 11 leads to draining the leakage water from the space above crown 11 directly through the passage 5 inside blade 2 and the opening 7 to a chamber which is located between the band 12 and the lower cover 14, which is designated by 16. This chamber 16 is connected to the low pressure side of the runner. The dash-dotted line on the left side of
Since opening 7 is ideally located at an equal or even slightly larger radial distance from the axis of rotation than the inlet aperture 6 backpressure is avoided due to the radial pumping effect of rotation.
For a similar reason the pressure distribution within the chamber 15 above the runner crown 11 is not uniform. The pressure is highest at the region of the highest distance and is lowest at the region of the smallest distance from the axis of rotation. Therefore, it is favorable, that the air inlet 10 is positioned in the head cover 1 at the smallest distance possible from the axis of rotation but outside the flange of the shaft that connects to the runner crown 11. At least the air inlet 10 is located at a diameter smaller than the locating diameter of the inlet aperture 6.
During operation of the hydraulic machine, air is sucked in through the air inlet 10 into the chamber 15 above the runner crown 11 or has to be pumped in by a compressor with little effort. This air partially fills the chamber 15 above the runner crown 11 forming an air cushion. From there air is transported by the water flow through the at least one passage 5 to the chamber 16 between band 12 and lower cover 14 forming an air cushion. Thus, air surrounds the periphery of the runner before flowing out into the water in the main flow passage exiting the hydraulic machine. As a result, friction losses, vibration and noise are reduced increasing the efficiency of the hydraulic machine.
By admitting the air at into the chamber 15 above the runner crown 11 above the rotating runner it will naturally accumulate, disperse and fill the chamber 15 until it reaches the passage 5 through the runner blade 2 where it will flow into the peripheral chamber 16. It enters the peripheral chamber 16 through the passage 5 in the rotation runner blade in an area where the flow velocity in the chamber is mainly in the peripheral direction, so it can also accumulate and provide good coverage of the outer surface of the rotating runner without necessitating a large mass-flow of air. Since the outer wall of the peripheral chamber 16 is at higher pressure, the air will be more concentrated close to the runner periphery where it is most beneficial for drag reduction.
Since many modernization projects of hydraulic machines involve the replacement of the turbine runner, the invention also has the advantage that it can be easily retrofitted to existing machines. The new runner would be provided with hollow blade passages according to the invention and the air inlet could easily be added to the head cover above the runner.
To further facilitate the airflow, the following modifications of the present invention may be applied (alone or in combination):
The blade could also be produced with a cavity directly by rapid prototyping methods such as additive manufacturing.
Filing Document | Filing Date | Country | Kind |
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PCT/EP2018/071616 | 8/9/2018 | WO | 00 |
Number | Date | Country | |
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62545135 | Aug 2017 | US | |
62713650 | Aug 2018 | US |