Large mixed-flow water turbine runner blade with two-section type water outlet edge wing section and runner

Abstract

A plurality of runner blades are annularly and uniformly distributed between an upper crown and a lower ring of the runner and are connected with the upper crown and the lower ring to form a whole, and a water outlet edge of each runner blade is formed by connecting a first airfoil section and a second airfoil section at a turning point P; the first airfoil section extends to the pressure surface side of the runner blade from the turning point P, and the second airfoil section extends to the suction surface side of the runner blade from the turning point P; the first airfoil section is a specific arc section, and the included angle theta 1 between the first airfoil section and the tangent point of the pressure surface is 10-20 degrees; the second airfoil section is a linear section, and the included angle theta 2 between the second airfoil section and the tangent point of the suction surface is 10-25 degrees; the length l of the second airfoil section is 1%-3% of the chord length L of the airfoil; the included angle theta 3 of the tangent points of the second airfoil section and the first airfoil section is 70-90 degrees; the two-section type water outlet edge can reduce the thickness of the runner blade, inhibit flow separation of the water outlet edge of the runner blade, improve the Karman vortex shedding frequency, avoid the inherent frequency range of the structure, reduce the flow separation intensity and achieve the purpose of reducing unit resonance.

Description

Technical Field

[0001] This invention belongs to the field of water turbine technology, and particularly relates to a large mixed-flow water turbine runner blade and runner with a two-section outlet side airfoil. Background Technology

[0002] The runner of a mixed-flow turbine is the core equipment in a hydropower station for converting water energy into mechanical energy. Its blades play a role in energy transfer: the dynamic torque generated by the water flow acting on the blade surface drives the runner to rotate, ultimately outputting shaft power. With the development of larger units, the hydrodynamic load on the blades has increased significantly. The water flow in the outlet region is prone to boundary layer separation due to factors such as geometry, flow velocity, and angle of attack, forming an unstable flow separation zone. This phenomenon has become the main source of induced hydraulic vibration, seriously threatening the safe operation of the unit.

[0003] Poor airfoil design in turbine runners can lead to flow separation at the blade trailing edge, with the alternating shedding of these separation vortices causing the formation of a Karman vortex street. When the vortex street frequency approaches or coincides with the natural frequency of the blade or adjacent components, it triggers strong hydraulic-elastic resonance. This not only causes abnormal vibration and noise in the unit but also significantly increases the alternating stress on critical components such as the blades, accelerating the initiation and propagation of fatigue cracks and significantly shortening the equipment's lifespan. Therefore, suppressing flow separation at the outlet edge and eliminating the Karman vortex street and its induced resonance risks are crucial for ensuring the long-term reliable operation of turbine runner blades.

[0004] In existing technologies, local modification of the outlet edge is carried out, that is, by changing the geometric characteristics of the outlet edge, the flow separation at the outlet edge is suppressed, the shedding frequency of the vortex street is increased, so that it avoids the natural frequency range of the structure, the flow separation intensity is reduced, the pressure pulsation amplitude is reduced, and the purpose of reducing unit resonance is achieved. Summary of the Invention

[0005] The purpose of this invention is to address the problems existing in the prior art summarized above by providing a large mixed-flow turbine runner blade and runner with a two-stage outlet airfoil. This method comprehensively considers operating conditions such as idling, no-load, and loaded operation. When calculating the counterweight, different operating conditions are assigned weights, and importance weights and target value weights are assigned to the measuring points. The planar vector composed of the counterweight and the magnitude and orientation of the measuring point's sway is transformed into a complex number form, and an overall objective function is established. Then, an optimization algorithm is used to solve the objective function, and the counterweight results are used to evaluate the impact under various operating conditions to determine whether further counterweight is needed until the requirements are met. This method can enable the unit to achieve the optimal comprehensive target for vibration and sway under different operating conditions, improve the active control capability for different operating conditions and different measuring points, thereby eliminating and improving the negative impact problems caused by the passive counterweight in the past.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A large mixed-flow turbine runner blade with a two-section outlet airfoil, wherein the outlet edge of the runner blade is formed by connecting a first airfoil section and a second airfoil section at a turning point P; the first airfoil section extends from the turning point P to the pressure surface side of the runner blade, and the second airfoil section extends from the turning point P to the suction surface side of the runner blade; the first airfoil section and the second airfoil section are the outlet edge airfoils of the runner blade at a cross-section of Span=0.5.

[0007] Preferably, the inflection point P is located at 92-98% of the chord length of the blade airfoil section, where the chord length is the straight-line distance from the leading edge to the trailing edge of the impeller blade within the cross-section at Span=0.5.

[0008] Preferably, the airfoil of the first airfoil segment (41) is defined by a function using the following curve: ; Where x and f(x) are the x and y coordinates of a point on the first airfoil segment in the Cartesian coordinate system.

[0009] Preferably, the second airfoil segment is a straight segment.

[0010] Preferably, the angle θ1 between the first airfoil segment and the tangent point of the pressure surface is 10°~20°.

[0011] Preferably, the angle θ2 between the second airfoil segment and the tangent point of the suction surface is 10°~25°.

[0012] Preferably, the length l of the second airfoil segment is 1% to 3% of the airfoil chord length L.

[0013] Preferably, the angle θ3 between the tangent point of the second airfoil segment and the first airfoil segment is 70°~90°.

[0014] The present invention also provides a large mixed-flow turbine runner with a two-section outlet airfoil, comprising multiple runner blades as described in any of the above claims, wherein the multiple runner blades are evenly distributed in a ring between the upper crown and the lower ring of the runner, forming an integral whole with the upper crown and the lower ring.

[0015] Compared with the prior art, the present invention has the following beneficial effects: The invention proposes a large mixed-flow turbine runner blade and runner with a two-section outlet airfoil. Multiple runner blades are evenly distributed in a ring between the upper crown and lower ring of the runner, forming a single unit. The outlet edge of the runner blade is formed by connecting a first airfoil section and a second airfoil section at a turning point P. The first airfoil section extends from turning point P to the pressure side of the runner blade, and the second airfoil section extends from turning point P to the suction side of the runner blade. The first and second airfoil sections refer to the outlet edge airfoil of the runner blade at the Span=0.5 section. The turning point P is located at 90-98% of the chord length of the airfoil section. The chord length is the distance from the leading edge to the trailing edge of the runner blade at the Span=0.5 section. The straight-line distance between the edge points; the first airfoil segment is a specific arc segment; the second airfoil segment is a straight-line segment; the airfoil curve of the first airfoil segment is defined by a function; the angle θ1 between the first airfoil segment and the tangent point of the pressure surface is 10°~20°; the angle θ2 between the second airfoil segment and the tangent point of the suction surface is 10°~25°; the length l of the second airfoil segment is 1%~3% of the airfoil chord length L; the angle θ3 between the second airfoil segment and the tangent point of the first airfoil segment is 70°~90°; both the pressure surface and suction surface of the runner blade are smooth transition curves; this outlet edge can reduce the thickness of the runner blade, suppress the flow separation at the outlet edge of the runner blade, increase the Karman vortex street shedding frequency, make it avoid the natural frequency range of the structure, reduce the flow separation intensity, and achieve the purpose of reducing unit resonance. Attached Figure Description

[0016] The invention will now be further described in detail with reference to the accompanying drawings and specific embodiments, wherein: Figure 1 This is a schematic diagram of the rotating wheel in this invention.

[0017] Figure 2 This is a schematic diagram of the Span surface of the present invention.

[0018] Figure 3 This is a cross-sectional view of the present invention with Span=0.5.

[0019] Figure 4 This is an enlarged schematic diagram of the water outlet edge of the Span=0.5 section of the present invention.

[0020] In the diagram: 1. Runner blade; 2. Upper crown; 3. Lower ring; 4. Water outlet edge; 41. First airfoil section; 42. Second airfoil section; 5. Pressure surface; 6. Suction surface. Detailed Implementation

[0021] To enable those skilled in the art to better understand the technical solutions of the present invention, embodiments of the present invention will be further described below with reference to the accompanying drawings. It should be noted that the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0022] It should be noted that span refers to the flow surface, which is the medium-span surface of the water flow area. It is a parameter that expresses the flow surface. span=0.5 represents the middle position of the flow channel, which is the representative flow plane.

[0023] As a preferred embodiment of the present invention, this embodiment provides a large mixed-flow turbine runner blade with a two-section outlet airfoil. The outlet edge 4 of the runner blade 1 is formed by connecting a first airfoil section 41 and a second airfoil section 42 at the inflection point P. The first airfoil section 41 extends from the inflection point P to the pressure surface 5 side of the runner blade, and the second airfoil section 42 extends from the inflection point P to the suction surface 6 side of the runner blade. The first airfoil section 41 and the second airfoil section 42 are the outlet edge 4 airfoils of the runner blade 1 at a cross-section of Span=0.5.

[0024] In the above embodiment S03, the turning point P is located at 92-98% of the chord length of the blade airfoil section, where the chord length is the straight-line distance from the leading edge to the trailing edge of the impeller blade 1 in the cross-section at Span=0.5.

[0025] The airfoil of the first airfoil segment 41 is defined by a function based on the following curve: ; Where x and f(x) are the x and y coordinates of a point on the first airfoil segment 41 in the Cartesian coordinate system.

[0026] Preferably, the second airfoil segment 42 is a straight segment.

[0027] In some preferred embodiments, the angle θ1 between the first airfoil segment 41 and the tangent point of the pressure surface 5 is 10°~20°, the angle θ2 between the second airfoil segment 42 and the tangent point of the suction surface 6 is 10°~25°, the length l of the second airfoil segment 42 is 1%~3% of the airfoil chord length L, and the angle θ3 between the second airfoil segment 42 and the tangent point of the first airfoil segment 41 is 70°~90°.

[0028] The water flow velocity and pressure distribution on the pressure side (water flow impact side) and suction side (low pressure side) of the impeller blades are significantly different: the water flow on the pressure side is driven by the blades, and the flow velocity is relatively stable but needs to transition smoothly to the outlet; the suction side is prone to backflow or vortex due to low pressure, resulting in energy loss.

[0029] In this invention, the first airfoil section extends to the pressure surface and adopts a function-defined curved airfoil, which can accurately match the flow trajectory of the water flow on the pressure surface, guide the water flow to smoothly transition to the outlet edge, and avoid local vortex losses caused by abrupt changes in trajectory. The second airfoil section extends to the suction surface and is set as a straight section. Combined with the angle design of θ2, it can suppress the backflow tendency in the low-pressure area of ​​the suction surface, force the water flow to flow out stably in a straight direction, reduce vortex and separation losses, and improve the overall hydraulic efficiency of the turbine.

[0030] This invention also provides a large mixed-flow turbine runner with a two-section outlet airfoil, characterized in that it includes multiple runner blades as described in any of the above embodiments, with the multiple runner blades 1 evenly distributed in a ring between the upper crown 2 and the lower ring 3 of the runner, forming an integral whole with the upper crown 2 and the lower ring 3.

[0031] The outlet edge is a critical area where water flows out of the blades and into the tailrace pipe. Its shape directly affects the uniformity of water flow and pressure pulsation, which can easily cause unit vibration.

[0032] The inflection point P is located at 92%~98% of the chord length. This two-section design focuses on the fine optimization of the tail end of the outlet: the curved shape of the first airfoil section and the straight shape of the second airfoil section are smoothly connected by the included angle θ3, avoiding the "acute angle change" or "excessive bending" that may occur in traditional single airfoils, and ensuring the consistency of the water flow direction at the outlet; at the same time, the length l of the second airfoil section is only 1%~3% of the chord length, which not only corrects the skew of the water flow on the suction surface through the straight section, but also avoids the interference of excessively long structures on the overall flow field, reduces pressure pulsation caused by uneven water flow, reduces the risk of unit vibration, and improves long-term operational stability.

[0033] The turbine runner provided by this invention, during use, allows water to flow through the leading edge of the turbine runner blades and into the tailrace pipe from the trailing edge. Numerical simulation analysis of the turbine runner blades revealed that a thicker fixed guide vane trailing edge and a blunt-edged outlet trailing edge design make flow separation more likely in the wake region, generating a Karman vortex street and resulting in hydraulic elastic resonance. Through numerical simulation analysis of various schemes, the following results were obtained: Figure 4 The shown outlet cross-sectional shape suppresses flow separation at the outlet of the turbine blades, increases the Karman vortex street shedding frequency, keeps it away from the structure's natural frequency range, reduces the shedding intensity, and achieves the goal of reducing unit resonance.

[0034] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A large mixed-flow turbine runner blade with a two-section outlet airfoil, characterized in that: The water outlet edge (4) of the impeller blade (1) is formed by connecting the first airfoil section (41) and the second airfoil section (42) at the turning point P; the first airfoil section (41) extends from the turning point P to the side of the pressure surface (5) of the impeller blade, and the second airfoil section (42) extends from the turning point P to the side of the suction surface (6) of the impeller blade; the first airfoil section (41) and the second airfoil section (42) are the water outlet edge (4) airfoils of the impeller blade (1) at Span=0.

5.

2. The large mixed-flow turbine runner blade with a two-section outlet airfoil as described in claim 1, characterized in that: The turning point P is located at 92-98% of the chord length of the airfoil section of the blade, where the chord length is the straight-line distance from the leading edge to the trailing edge of the rotor blade (1) in the cross section at Span=0.

5.

3. The large mixed-flow turbine runner blade with a two-section outlet airfoil as described in claim 1, characterized in that: The airfoil of the first airfoil segment (41) is defined by a function using the following curve: ； Where x and f(x) are the x and y coordinates of the points on the first airfoil segment (41) in the Cartesian coordinate system.

4. The large mixed-flow turbine runner blade with a two-section outlet airfoil as described in claim 1, characterized in that: The second airfoil segment (42) is a straight segment.

5. The large mixed-flow turbine runner blade with a two-section outlet airfoil as described in claim 1, characterized in that: The angle θ1 between the first airfoil segment (41) and the tangent point of the pressure surface (5) is 10°~20°.

6. The large mixed-flow turbine runner blade with a two-section outlet airfoil as described in claim 1, characterized in that: The angle θ2 between the second airfoil segment (42) and the tangent point of the suction surface (6) is 10°~25°.

7. The large mixed-flow turbine runner blade with a two-section outlet airfoil as described in claim 1, characterized in that: The length l of the second airfoil segment (42) is 1% to 3% of the airfoil chord length L.

8. The large mixed-flow turbine runner blade with a two-section outlet airfoil as described in claim 1, characterized in that: The angle θ3 between the tangent point of the second airfoil segment (42) and the first airfoil segment (41) is 70°~90°.

9. A large mixed-flow turbine runner with a two-stage outlet side airfoil, characterized in that: It includes multiple impeller blades as described in any one of claims 1-8, wherein multiple impeller blades (1) are evenly distributed in a ring between the upper crown (2) and the lower ring (3) of the impeller, forming a whole with the upper crown (2) and the lower ring (3).

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