Method for inhibiting internal cavitation erosion of runner of mixed-flow water turbine and runner of mixed-flow water turbine

Abstract

The invention relates to the technical field of fluid machinery, and discloses a mixed-flow water turbine runner internal cavitation inhibition method and a mixed-flow water turbine runner, and the method comprises the following steps: arranging an air hole group in an easy cavitation area on the back surface of a runner blade; when the water turbine operates in the cavitation risk working condition, air is actively supplemented to the surfaces of the blades through the air hole sets; and the sprayed gas forms a gas film tightly attached to the wall surface on the surface of the blade so as to inhibit the corrosion of cavitation erosion to the blade. An air film is formed on the surface of the runner blade through an air supply method, so that the blade surface is protected, and cavitation erosion is restrained. The overall arrangement of the method is as shown in Figure 1 and Figure 2, some air holes are formed in the blades in the Figure 1, and when the water turbine operates under the cavitation risk working condition, air injection can be achieved by controlling the air holes. The sprayed gas forms a gas film tightly attached to the metal wall surface at the position, where cavitation erosion is prone, of the blade, so that the blade is protected against corrosion, or the corrosion degree is reduced.

Description

Technical Field

[0001] This invention relates to the field of fluid machinery technology, specifically to a method for suppressing cavitation inside a mixed-flow turbine runner and a mixed-flow turbine runner. Background Technology

[0002] Cavitation erosion is a problem in mixed-flow turbines. When the unit operates under non-design conditions, cavitation occurs when the pressure at certain locations inside the runner is lower than the cavitation pressure, forming bubbles. When these bubbles flow through areas of higher pressure, they collapse, forming microjet streams that impact nearby metal walls. These microjet streams erode the metal walls using thermodynamic and electrochemical principles, resulting in cavitation erosion.

[0003] Cavitation erosion in mixed-flow turbines mainly includes airfoil cavitation erosion, which mainly affects the lower half of the blade back surface, the connection between the blade back surface and the lower ring, the inner side of the lower ring vertical surface, the junction between the blade back surface and the upper crown, as well as cavity cavitation, i.e., tailrace tube cavitation.

[0004] For the tailrace vortex phenomenon of mixed-flow turbines, power plants generally adopt the main shaft air supply method. By utilizing the low-pressure characteristics of the tailrace vortex, natural or forced air supply is used to supply air to the tailrace vortex to reduce the cavitation effect.

[0005] However, this method is primarily effective only in addressing cavitation erosion in the tailrace tube, and has virtually no effect on cavitation erosion in the turbine runner. For airfoil cavitation erosion, i.e., cavitation erosion in the runner, hydropower stations currently mainly employ reactive maintenance methods. After cavitation has occurred, the unit is shut down for maintenance, and severely cavitated blades are repaired through welding or other repair measures. In terms of protecting the runner from cavitation erosion, the main methods are passive measures such as improving hydraulic design performance, enhancing blade material properties, using anti-cavitation coatings, and limiting the operating time in the cavitation zone. There is still a lack of active protection methods for cavitation erosion within the runner. Summary of the Invention

[0006] In view of this, the present invention provides a mixed-flow turbine runner and a method for suppressing cavitation inside the mixed-flow turbine runner, so as to solve the problem of protecting the runner from cavitation.

[0007] In a first aspect, the present invention provides a method for suppressing cavitation inside the runner of a mixed-flow turbine, comprising the following steps: A pore group is set in the cavitation-prone area on the back of the runner blade; When the turbine is operating under cavitation risk conditions, air is actively supplied to the blade surface through the pore group; The ejected gas forms a gas film that adheres tightly to the blade surface, thus inhibiting cavitation corrosion of the blade.

[0008] In one optional implementation, the cavitation-prone region includes at least one of the following locations: The high-pressure edge region at the junction of the blade back and the upper crown; The area where the blade's back meets the lower ring; The lower half of the back of the blade, near the water's edge.

[0009] This method for suppressing cavitation inside the runner of a mixed-flow turbine utilizes an air-injection method to form an air film on the surface of the runner blades, thereby protecting the blade surface and suppressing cavitation. The overall arrangement of this method is as follows: Figure 1 and Figure 2 As shown in the diagram, the blades are equipped with pores. When the turbine operates under cavitation risk conditions, air can be ejected through these pores. The ejected gas forms a gas film that adheres tightly to the metal wall at the cavitation-prone areas of the blade, protecting the blade from corrosion or reducing the degree of corrosion.

[0010] In one optional embodiment, the pore group includes: The turbine crown vent group is located in the high-pressure edge zone near the junction of the back of the blade and the crown. The runner lower ring air hole group is provided in the area where the back of the blade connects with the lower ring; The runner outlet air hole group is set in the lower half of the water outlet area on the back of the blade.

[0011] In one optional embodiment, the cross-section of the pores and / or the gas flow channels connected thereto of the pore group is flat, and the length L1 and height L2 of the cross-section satisfy the relationship: L1≥3L2.

[0012] The pores of the pore group and the gas flow channels connected to them are designed with a flat cross-section. This design allows the gas to form a wide but thin airflow when ejected. From an operational perspective, this flat cross-sectional structure allows the gas to be ejected in a specific shape, making it easier to spread out in specific areas on the blade surface. In terms of effect, the wider airflow can cover a larger area, thus forming a gas film of a certain area in the areas of the blade prone to cavitation, effectively isolating cavitation bubbles from direct contact with the metal wall of the blade; the thinner airflow reduces interference with the mainstream water flow in the runner, avoiding a significant impact on the normal hydrodynamic performance of the turbine due to excessively thick airflow. While achieving cavitation suppression, it also maintains the turbine's operating efficiency as much as possible.

[0013] In one alternative embodiment, the flat cross-section is elliptical or rounded rectangular.

[0014] Flat cross-sections employ elliptical or rounded rectangular designs. Their streamlined contours reduce gas flow resistance, allowing the gas to be ejected more smoothly. Rounded rectangular cross-sections, with their rounded corners, avoid airflow separation or turbulence that can occur with right-angled structures, similarly ensuring smooth gas flow. Both cross-sectional shapes allow the ejected gas to form a wide and thin airflow. The elliptical cross-section provides a more uniform airflow diffusion range, while the coverage width of the airflow in a specific direction with the rounded rectangular cross-section can be further optimized by adjusting the long side.

[0015] In one alternative embodiment, the direction in which the gas is ejected from the vent forms a jet angle θ with the blade surface near the vent, and the value of θ ranges from 30° to 50°.

[0016] From an operational perspective, this angle range allows the ejected gas to cut into the water flow area near the blade surface at an angle. When the gas jet is ejected at an angle of 30° to 50°, on the one hand, it can utilize the initial kinetic energy of the airflow to allow the gas to quickly spread close to the blade surface after leaving the vent; on the other hand, this angle can balance the interaction between the gas jet and the mainstream water flow—if the angle is too small (e.g., less than 30°), the airflow may be entrained by the mainstream too early and fail to effectively adhere to the blade surface, while if the angle is too large (e.g., more than 50°), the airflow may cause excessive disturbance due to the impact with the mainstream.

[0017] In one alternative implementation, the angle α between the jet direction of the gas ejected from the vent and the mainstream direction at that location within the rotor satisfies: 140°≤α≤180°.

[0018] When the included angle α is within this range, the direction of the ejected gas jet is nearly opposite to the direction of the mainstream (180° is completely opposite, and 140° forms a large obtuse angle). At this time, the high-speed flowing mainstream water will first block the gas jet ejected in the opposite direction, forcing the airflow speed to decrease rapidly. Then, under the influence of the mainstream, the gas jet changes direction and gradually flows towards the mainstream along the blade surface. During this process, the gas jet is "suppressed" in the area near the blade surface through its interaction with the mainstream, making it easier to form a continuous gas film at the target protection location (such as the back of the blade, the inner side of the lower ring, and other cavitation-sensitive areas).

[0019] In one alternative implementation, the gas flow channel is integrated into the blade in one of the following ways: A tubular structure is formed by casting inside the blade; External pipes are welded or embedded on the blade surface.

[0020] By directly embedding the gas flow channel into the blade body through the casting process, the flow channel and the blade material become one. This method can ensure the stability and sealing of the flow channel structure, avoid leakage problems at the joint surface caused by later installation, and at the same time reduce the impact on the smoothness of the flow channel surface and reduce gas flow resistance.

[0021] Alternatively, prefabricated pipe structures can be attached to the blade surface by machining mounting grooves or welding fasteners. This method is highly flexible and suitable for upgrading existing blades without changing the overall blade casting process. Flow channels can be arranged in specific areas according to cavitation protection requirements, and it is convenient for later maintenance or pipe replacement.

[0022] In one alternative embodiment, the gas flow channel is connected to a main gas channel arranged at the trailing edge of the blade.

[0023] The main gas channel is installed at the trailing edge of the blade, a region typically where the runner's hydrodynamic influence is minimal, thus reducing interference with the blade's mainstream flow and structural strength. As the main path for gas input, the main gas channel connects to internal gas channels within the blade (such as the channels corresponding to the crown orifice group, lower ring orifice group, and water outlet edge orifice group on the runner) via branch structures, forming a gas supply network.

[0024] In one alternative embodiment, the supplementary gas is air or an inert gas.

[0025] Secondly, the present invention also provides a mixed-flow turbine runner for implementing the method for suppressing cavitation inside the mixed-flow turbine runner, comprising an upper crown, a lower ring, and multiple blades connected between the upper crown and the lower ring; The cavitation-prone area on the back of the blade is provided with a group of pores, which are connected to a gas source through gas channels integrated inside or on the surface of the blade.

[0026] When the unit is operating in the cavitation zone, the mixed-flow turbine runner can inject gas through the pore group to form a continuous gas film on the surface of the blade's easily corroded area. This actively blocks the impact of micro-jet generated by the collapse of cavitation bubbles, thereby inhibiting cavitation erosion of the blades, improving the runner's cavitation resistance, reducing maintenance costs, and ensuring the safe operation of the unit. Attached Figure Description

[0027] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0028] Figure 1This is a front view of a mixed-flow turbine runner according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the structure of the blades of a mixed-flow turbine runner according to an embodiment of the present invention; Figure 3 This is a cross-sectional view of the air holes and gas flow channels in a mixed-flow turbine runner according to an embodiment of the present invention; Figure 4 This is a cross-sectional view of the air holes and gas flow channels in a mixed-flow turbine runner according to an embodiment of the present invention; Figure 5 This is a schematic diagram showing the angular relationship between the supplementary airflow and the mainstream water flow in a mixed-flow turbine runner according to an embodiment of the present invention.

[0029] Explanation of reference numerals in the attached figures: 1. Crown vent assembly on the rotor; 2. Lower ring air hole assembly of the impeller; 3. Air vent assembly at the water outlet of the impeller; 4. Gas flow channel; 5. Main gas passage; 6. Leaves. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] Cavitation erosion is a problem in mixed-flow turbines. When the unit operates under non-design conditions, cavitation occurs when the pressure at certain locations inside the runner is lower than the cavitation pressure, forming bubbles. When these bubbles flow through areas of higher pressure, they collapse, forming microjet streams that impact nearby metal walls. These microjet streams erode the metal walls using thermodynamic and electrochemical principles, resulting in cavitation erosion.

[0032] Cavitation erosion in mixed-flow turbines mainly includes airfoil cavitation erosion, which mainly affects the lower half of the blade back surface, the connection between the blade back surface and the lower ring, the inner side of the lower ring vertical surface, the junction between the blade back surface and the upper crown, as well as cavity cavitation, i.e., tailrace tube cavitation.

[0033] For the tailrace vortex phenomenon of mixed-flow turbines, power plants generally adopt the main shaft air supply method. By utilizing the low-pressure characteristics of the tailrace vortex, natural or forced air supply is used to supply air to the tailrace vortex to reduce the cavitation effect.

[0034] However, this method is primarily effective only in addressing cavitation erosion in the tailrace tube, and has virtually no effect on cavitation erosion in the turbine runner. For airfoil cavitation erosion, i.e., cavitation erosion in the runner, hydropower stations currently mainly employ reactive maintenance methods. After cavitation has occurred, the unit is shut down for maintenance, and severely cavitated blades are repaired through welding or other repair measures. In terms of protecting the runner from cavitation erosion, the main methods are passive measures such as improving hydraulic design performance, enhancing blade material properties, using anti-cavitation coatings, and limiting the operating time in the cavitation zone. There is still a lack of active protection methods for cavitation erosion within the runner.

[0035] The following is combined with Figures 1 to 5 The following describes embodiments of the present invention.

[0036] According to an embodiment of the present invention, a method for suppressing cavitation inside a mixed-flow turbine runner is provided, comprising the following steps: A group of pores is set in the cavitation-prone area on the back of the runner blade 6; When the turbine is operating under cavitation risk conditions, air is actively supplied to the surface of blade 6 through the air hole group; The ejected gas forms a gas film that adheres tightly to the wall surface of blade 6, thereby inhibiting cavitation corrosion of blade 6.

[0037] This method for suppressing cavitation inside the runner of a mixed-flow turbine utilizes an air-injection method to form an air film on the surface of the runner blades 6, thereby protecting the blade surface and suppressing cavitation. The overall arrangement of this method is as follows: Figure 1 and Figure 2 As shown in the figure, some pores are arranged on the blade 6. When the turbine is operating under cavitation risk conditions, air can be ejected by controlling the pores. The ejected gas forms a gas film that adheres tightly to the metal wall at the cavitation-prone areas of the blade 6, thus protecting the blade 6 from corrosion or reducing the degree of corrosion.

[0038] For example, micropores with a diameter of 0.5 mm are machined as a pore group in the cavitation-prone area on the back of the runner blade 6 of a mixed-flow turbine, with the pore depth being 1 / 3 of the blade 6 thickness. The pores can be achieved by laser drilling.

[0039] In one embodiment, the cavitation-prone region includes at least one of the following locations: The high-pressure edge region near the junction of the back surface of blade 6 and the upper crown; The area where the back of blade 6 connects to the lower ring; The lower half of the back of blade 6 is located at the water outlet.

[0040] For example, the upper crown junction area can be the high-pressure side of the back of blade 6, 10mm below the upper crown weld seam; the lower ring connection area can be the abrupt change in the radius of curvature where the inner curved surface of the lower ring transitions to the back of blade 6; the water outlet area can be within 30% of the blade height above the end of the water outlet edge on the back of blade 6. The above values ​​are all illustrative examples. In actual operation, the range of the three areas can be changed according to the needs of the site.

[0041] In the above embodiments, targeted air replenishment is used to improve the air film coverage and avoid flow loss caused by ineffective air replenishment.

[0042] In one embodiment, the pore assembly includes: The runner crown vent group 1 is located in the high-pressure edge zone near the junction of the back of blade 6 and the crown. The runner lower ring air hole group 2 is located in the area where the back of the blade 6 connects with the lower ring; The runner outlet air hole group 3 is located on the lower half of the water outlet area on the back of blade 6.

[0043] by Figure 2 The structure shown is illustrated as follows: the upper crown vent group 1 of the runner consists of two vents located in the high-pressure side area near the junction of the back of the blade 6 and the upper crown; the lower ring vent group 2 of the runner consists of two vents located in the area connecting the back of the blade 6 and the lower ring; and the water outlet side vent group 3 of the runner consists of four vents located in the lower half water outlet side area on the back of the blade 6.

[0044] like Figure 4 As shown, in one embodiment, the cross-section of the pores of the pore group and / or the gas flow channel 4 connected thereto is flat, and the length L1 and height L2 of the cross-section satisfy the relationship: L1≥3L2.

[0045] In this embodiment, the cross-sections of the pores in the pore group and the gas flow channel 4 connected to them are designed to be flat. This design allows the gas to form a wide but thin airflow when ejected. From an operational perspective, this flat cross-sectional structure allows the gas to be ejected in a specific shape, making it easier to spread out in specific areas on the surface of the blade 6. In terms of effect, the wider airflow can cover a larger area, thereby forming a gas film of a certain area in the areas of the blade 6 prone to cavitation, effectively isolating cavitation bubbles from direct contact with the metal wall of the blade 6; the thinner airflow can reduce interference with the mainstream water flow in the runner, avoiding a significant impact on the normal hydrodynamic performance of the turbine due to excessively thick airflow, thus suppressing cavitation while maintaining the turbine's operating efficiency as much as possible. Preferably, the length L1 and height L2 of the cross-section need to satisfy the relationship L1≥3L2.

[0046] In one embodiment, the flat cross-section is elliptical or rounded rectangular.

[0047] Flat cross-sections employ elliptical or rounded rectangular designs. Their streamlined contours reduce gas flow resistance, allowing the gas to be ejected more smoothly. Rounded rectangular cross-sections, with their rounded corners, avoid airflow separation or turbulence that can occur with right-angled structures, similarly ensuring smooth gas flow. Both cross-sectional shapes allow the ejected gas to form a wide and thin airflow. The elliptical cross-section provides a more uniform airflow diffusion range, while the coverage width of the airflow in a specific direction with the rounded rectangular cross-section can be further optimized by adjusting the long side.

[0048] like Figure 3 As shown, in one embodiment, the direction in which the gas is ejected from the vent forms a jet angle θ with the surface of the blade 6 near the vent, and the value of θ ranges from 30° to 50°. For example, 30°, 40°, or 50°.

[0049] From an operational perspective, this angle range allows the ejected gas to cut into the water flow area near the surface of blade 6 at an angle. When the gas jet is ejected at an angle of 30° to 50°, on the one hand, it can utilize the initial kinetic energy of the airflow to allow the gas to quickly spread close to the surface of blade 6 after leaving the vent; on the other hand, this angle can balance the interaction between the gas jet and the mainstream water flow—if the angle is too small (e.g., less than 30°), the airflow may be entrained by the mainstream too early and fail to effectively adhere to the surface of blade 6, while if the angle is too large (e.g., more than 50°), the airflow may cause excessive disturbance due to the impact with the mainstream.

[0050] like Figure 5 As shown, in one embodiment, the angle α between the jet direction of the gas ejected from the vent and the mainstream direction at that position inside the rotor satisfies: 140°≤α≤180°.

[0051] When the included angle α is within this range, the direction of the ejected gas jet is nearly opposite to the direction of the mainstream (180° is completely opposite, and 140° forms a large obtuse angle). At this time, the high-speed flowing mainstream water will first block the gas jet ejected in the opposite direction, forcing the airflow speed to decrease rapidly. Then, under the influence of the mainstream, the gas jet changes direction and gradually flows towards the mainstream along the surface of blade 6. During this process, the gas jet is "suppressed" in the area near the surface of blade 6 through its interaction with the mainstream, making it easier to form a continuous gas film at the target protection location (such as the back of blade 6, the inner side of the lower ring, and other cavitation-sensitive areas).

[0052] The larger angle allows the gas jet to interact strongly with the mainstream in the initial stage, ensuring that the airflow does not deviate from the protected area by following the mainstream too early, thus accurately covering the part of the blade that is susceptible to cavitation erosion.

[0053] In one embodiment, the gas flow channel 4 is integrated into the interior of the blade 6 in one of the following ways: A pipe structure is formed inside the blade 6 by casting: the gas flow channel 4 is directly embedded into the blade 6 body through the casting process, so that the flow channel and the blade 6 material become one. This method can ensure the stability and sealing of the flow channel structure, avoid leakage problems at the joint surface caused by later installation, and reduce the impact on the smoothness of the flow channel surface, thereby reducing the gas flow resistance.

[0054] External pipes can be welded or embedded on the surface of blade 6. By machining mounting grooves or welding fasteners on the surface of blade 6, prefabricated pipe structures can be attached to the surface of blade 6. This method is highly flexible and suitable for the modification and upgrading of existing blades 6. It does not require changing the overall casting process of blade 6. Flow channels can be arranged in specific areas according to the cavitation protection requirements, and it is convenient for later maintenance or pipe replacement.

[0055] like Figure 2 As shown, in one embodiment, the gas flow channel 4 is connected to the main gas channel 5 arranged at the trailing edge of the blade 6.

[0056] The main gas channel 5 is installed at the trailing edge of the blade 6. This area is usually less affected by the hydrodynamics of the runner, which can reduce interference with the main flow and structural strength of the blade 6. As the main path for gas input, the main gas channel 5 is connected to the gas flow channels 4 inside the blade 6 (such as the flow channels corresponding to the crown gas hole group 1, the lower ring gas hole group, and the water outlet edge gas hole group on the runner) through branch structures, forming a gas supply network.

[0057] In one embodiment, the replenishing gas is air or an inert gas.

[0058] According to an embodiment of the present invention, another aspect provides a mixed-flow turbine runner for implementing a method to suppress cavitation erosion inside the mixed-flow turbine runner. The mixed-flow turbine runner includes an upper crown, a lower ring, and multiple blades 6 connected between the upper crown and the lower ring. A group of pores is provided in the cavitation-prone area on the back surface of the blades 6. The pore group is connected to a gas source through a gas flow channel 4 integrated inside or on the surface of the blades 6. The cross-sectional shape of the flow channel and the jet angle configuration satisfy the aforementioned conditions for gas film formation.

[0059] The runner consists of an upper crown, a lower ring, and multiple blades 6 connecting the two. A series of pores are installed on the surface of the blades 6, specifically targeting areas prone to cavitation erosion on their back surfaces (such as the lower half of the blade 6's back surface, the connection between the blade 6's back surface and the lower / upper crown, and the inner side of the lower ring's vertical surface). These pores connect to an external air source via gas channels 4 integrated inside or on the surface of the blades 6, forming an air supply path. Specifically: The cross-sectional shape of the flow channel must meet the requirements of a flat design (such as an ellipse or a rounded rectangle), and the cross-sectional length L1 and height L2 must satisfy L1≥3L2 to ensure that a wide and thin airflow is formed when the gas is ejected, so as to cover a larger protective area and reduce interference with the mainstream.

[0060] Jet angle configurations include: Jet angle θ: The angle between the direction of gas ejection from the vent and the surface of blade 6 is 30°-50°, so that the airflow cuts into the water flow at an inclined attitude, balances the kinetic energy of the gas and the effect of the mainstream, and ensures that the gas film is stably attached to the surface of blade 6. Angle α between jet direction and mainstream: The angle between the gas jet direction and the mainstream direction at this position inside the impeller is 140°-180°. By utilizing the blocking and entraining effect of the mainstream water flow, the gas is "pressed" near the surface of blade 6, precisely forming a protective gas film.

[0061] Through the above structural design, the mixed-flow turbine runner can inject gas through the pore group when the unit is operating in the cavitation zone, forming a continuous gas film on the surface of the easily corroded area of ​​the blade 6, actively blocking the impact of micro-jet generated by the collapse of cavitation bubbles, thereby inhibiting cavitation erosion of the blade 6, improving the runner's anti-cavitation performance, reducing maintenance costs and ensuring the safe operation of the unit.

[0062] Although embodiments of the invention have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of the invention, and such modifications and variations all fall within the scope defined by the appended claims.

Claims

1. A method for suppressing cavitation inside the runner of a mixed-flow turbine, characterized in that, Includes the following steps: A pore group is set in the cavitation-prone area on the back of the blade (6); When the turbine is operating under cavitation risk conditions, air is actively supplied to the surface of the blade (6) through the pore group; The ejected gas forms a gas film that adheres closely to the wall surface on the blade (6) to suppress cavitation corrosion of the blade (6).

2. The method for suppressing cavitation inside the runner of a mixed-flow turbine according to claim 1, characterized in that, The cavitation-prone area includes at least one of the following locations: The area near the high-pressure edge at the junction of the back of the blade (6) and the upper crown; The area where the back of the blade (6) connects to the lower ring; The lower half of the back of the blade (6) is above the water.

3. The method for suppressing cavitation inside the runner of a mixed-flow turbine according to claim 2, characterized in that, The pore group includes: The rotor crown vent group (1) is located in the high-pressure side zone near the junction of the back of the blade (6) and the crown. The lower ring air hole group (2) is set in the area where the blade (6) connects to the lower ring. The impeller outlet air hole group (3) is set in the lower half of the water outlet area on the back of the blade (6).

4. The method for suppressing cavitation inside the runner of a mixed-flow turbine according to any one of claims 1-3, characterized in that, The cross-section of the pores and / or the gas flow channel (4) connected to the pore group is flat, and the length L1 and height L2 of the cross-section satisfy the relationship: L1≥3L2.

5. The method for suppressing cavitation inside the runner of a mixed-flow turbine according to claim 4, characterized in that, The flat cross-section is elliptical or rounded rectangular.

6. The method for suppressing cavitation inside the runner of a mixed-flow turbine according to any one of claims 1-5, characterized in that, The direction of the gas ejected from the vent forms a jet angle θ with the surface of the blade (6) near the vent, and the value of θ ranges from 30° to 50°.

7. The method for suppressing cavitation inside the runner of a mixed-flow turbine according to any one of claims 1-6, characterized in that, The angle α between the direction of the gas jet ejected from the vent and the mainstream direction at that position inside the rotor satisfies: 140°≤α≤180°.

8. The method for suppressing cavitation inside the runner of a mixed-flow turbine according to any one of claims 4-7, characterized in that, The gas flow channel (4) is integrated into the interior of the blade (6) by one of the following methods: A pipe structure is formed inside the blade (6); External pipes are welded or embedded on the surface of the blade (6).

9. The method for suppressing cavitation inside the runner of a mixed-flow turbine according to claim 4, characterized in that, The gas flow channel (4) is connected to the main gas channel (5) arranged at the trailing edge of the blade (6).

10. The method for suppressing cavitation inside the runner of a mixed-flow turbine according to any one of claims 1-9, characterized in that, The supplementary gas is air or an inert gas.

11. A mixed-flow turbine runner, used to realize the internal structure of the mixed-flow turbine runner according to any one of claims 1-10. The cavitation erosion suppression method is characterized by, It includes an upper crown, a lower ring, and multiple blades (6) connecting the upper crown and the lower ring; The cavitation-prone area on the back of the blade (6) is provided with a group of pores, which are connected to the gas source through a gas flow channel (4) integrated inside or on the surface of the blade (6).

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