A method and structure for shaping the root of the bucket of an impulse turbine.

Abstract

This invention belongs to the field of water turbine technology, and specifically relates to a method and structure for shaping the root of an impulse turbine bucket. The shaping method includes the following steps: the middle and both sides of the bucket root are connected to the curved surface of the bucket using cylindrical surfaces; boundary conditions and loads are applied, and finite element analysis is performed on the bucket; based on the stress results, the bucket root is divided into a high-stress zone in the middle and general stress zones on both sides; auxiliary sections and control lines are added to the high-stress zone, and a saddle-shaped stress-reducing structure with a truncated top is constructed using curve groups or curve meshes; the saddle-shaped stress-reducing structure is connected to the front and back sides of the bucket root in the general stress zone by rounding; the saddle-shaped stress-reducing structure is bridged to the cylindrical surface of the general stress zone using bridging surfaces. This invention provides a method and structure for shaping the root of an impulse turbine bucket that can effectively reduce the stress level in the high-stress zone of the bucket root, enhance its versatility and operability, and reduce the development cycle of the bucket.

Description

Technical Field

[0001] This invention belongs to the field of water turbine technology, and specifically relates to a method and structure for shaping the root of the bucket of an impulse water turbine. Background Technology

[0002] The bucket is one of the core components of an impulse turbine, and its structure is complex with dramatic surface changes. During unit operation, the bucket is subjected to enormous alternating loads, making it highly susceptible to cracking or even bucket breakage. The high-stress zone formed at the bucket root is a major cause of this accident; therefore, it is essential to optimize the design of the high-stress area of ​​the bucket and strictly control the static and dynamic stress levels in this area.

[0003] Currently, most water bucket base designs simply use a cylindrical surface to transition between the cylindrical surface and the curved surface at the base of the water bucket (see...). Figure 7 This method can only ensure a smooth transition between the various curved surfaces at the root of the bucket, but it cannot guarantee a low stress level or uniform stress distribution. The advantage of this structure is its simple shape, but the disadvantage is that it does not consider the influence of the local stiffness of the transition surface on the stress distribution, and its effect on reducing bucket stress is not obvious. With the increase in the single unit capacity and design head of impulse turbines, this method can no longer meet the current design requirements.

[0004] like Figure 6 The design process flowchart also includes a small number of designs that optimize the structure step by step, targeting the main factors affecting the stress level at the root of the water bucket. The advantage of this design method is that it can effectively reduce the stress level in the high-stress area of ​​the water bucket. The disadvantage is that the design method is complex and has poor versatility and operability, which greatly prolongs the development cycle of the water bucket. Summary of the Invention

[0005] In order to solve the above-mentioned problems in the prior art, the purpose of this invention is to provide a method and structure for shaping the root of an impulse turbine bucket that can effectively reduce the stress level in the high-stress area at the bucket root and enhance its versatility and operability to reduce the development cycle of the bucket.

[0006] The technical solution adopted in this invention is as follows:

[0007] A method for shaping the root of the bucket of an impulse turbine includes the following steps:

[0008] The middle and both sides of the water bucket root are connected by a cylindrical surface and the curved surface of the water bucket to form the basic structure of the water bucket root.

[0009] Boundary conditions and loads are applied to the water bucket, finite element analysis is performed on the water bucket, and stress results are extracted.

[0010] Based on the stress results, the root of the water bucket is divided into a high-stress zone in the middle and general-stress zones on both sides.

[0011] Add auxiliary sections and control lines in high-stress areas, and construct a saddle-shaped stress-reducing structure with a truncated top by using curve groups or curve grids;

[0012] Within the general stress zone, it is connected to the front and back of the water bucket root by rounding.

[0013] The saddle-shaped stress-reducing structure is bridged with the cylindrical surface of the general stress zone through a bridging surface, so that the saddle-shaped stress-reducing structure and the general stress zone have a smooth transition.

[0014] The method for shaping the root of the impact turbine bucket of the present invention first divides the root area of ​​the bucket into a high-stress area and a general stress area. In the high-stress area, auxiliary sections and control lines are added, and a saddle-shaped stress-reducing structure with a sloping top is constructed by a group of curves or a curve grid. In the general stress area, the bucket root is connected to the front and back sides by a rounding method with a variable radius. Finally, the general stress area and the high-stress area are bridged by a bridging surface to make the various curved surfaces transition smoothly.

[0015] This invention artificially divides the water bucket root into two parts—a high-stress zone and a general stress zone—based on the stress distribution. In the high-stress zone, a saddle-shaped stress-reducing structure with a truncated top is employed. This truncated top structure is equivalent to removing the top of a cylindrical structure, effectively reducing the stress level in the high-stress zone. In the general stress zone, a cylindrical surface is constructed and then connected to the front and back sides of the water bucket root using a rounded design with a variable radius, resulting in a simple structure.

[0016] The present invention is highly operable and versatile, and can be applied to impulse turbine units of various capacities and heads; its simple design greatly reduces the development cycle of the water bucket.

[0017] As a preferred embodiment of the present invention, the top of the cross-section of the constructed saddle-shaped stress-reducing structure is an upwardly convex arc, and the curvature of the top of the cross-section of the saddle-shaped stress-reducing structure is greater than the curvature of the top of the cross-section of the cylindrical water bucket root before constructing the saddle-shaped stress-reducing structure. In the first form of the saddle-shaped stress-reducing structure, the top of the cross-section of the saddle-shaped stress-reducing structure is an upwardly convex arc, but its curvature is larger, and compared with the cylindrical structure, its top still has part of the structure cut off.

[0018] In a preferred embodiment of the present invention, the top of the cross-section of the constructed saddle-shaped stress-reducing structure is a straight line. In the second type of saddle-shaped stress-reducing structure, the top of the cross-section of the saddle-shaped stress-reducing structure is a straight line; compared to the cylindrical structure, the second type of saddle-shaped shear stress-reducing structure has its top removed.

[0019] As a preferred embodiment of the present invention, the top of the cross-section of the constructed saddle-shaped stress-reducing structure is a downwardly concave arc. In the third type of saddle-shaped stress-reducing structure, the top of the cross-section of the saddle-shaped stress-reducing structure is a downwardly concave arc. Compared with the cylindrical structure, the third type of saddle-shaped shear stress-reducing structure has a larger top portion removed.

[0020] As a preferred embodiment of the present invention, the top and sides of the constructed saddle-shaped stress-reducing structure have a smooth transition. When constructing the three types of saddle-shaped shear stress structures, the top and sides of the saddle-shaped stress-reducing structure must have a smooth transition. That is, the entire area of ​​the curve group or curve grid is an arc, so that the constructed saddle-shaped shear stress structure can effectively reduce the stress level in the high-stress area of ​​the water bucket, and also make the stress-reducing area smoothly transition with other areas. By constructing the curve group or curve grid in one go, the step of designing the smooth transition separately is avoided.

[0021] As a preferred embodiment of the present invention, when connecting the front and back sides of the water bucket root in a rounded manner within a general stress zone, a rounded manner with a variable radius is adopted.

[0022] A bucket root structure for an impulse turbine includes a high-stress zone and a general-stress zone. The high-stress zone is a saddle-shaped stress-reducing structure with a truncated top. The general-stress zone is connected to the front and back sides of the bucket root through a rounded section with a variable radius.

[0023] This invention artificially divides the water bucket root into two parts—a high-stress zone and a general stress zone—based on the stress distribution. The high-stress zone at the water bucket root is a saddle-shaped stress-reducing structure with a truncated top. This truncated top structure is equivalent to removing the top of a cylindrical structure, effectively reducing the stress level in the high-stress zone. A cylindrical surface is constructed in the general stress zone and then connected to the front and back sides of the water bucket root using a rounded design with a variable radius, resulting in a simple structure.

[0024] As a preferred embodiment of the present invention, the top of the cross-section of the saddle-shaped stress-reducing structure is an upwardly convex arc, a straight line, or a downwardly concave arc; when the top of the cross-section of the saddle-shaped stress-reducing structure is an upwardly convex arc, the curvature of the top of the cross-section of the saddle-shaped stress-reducing structure is greater than the curvature of the top of the cross-section of the cylindrical water bucket root before constructing the saddle-shaped stress-reducing structure.

[0025] As a preferred embodiment of the present invention, the top and sides of the saddle-shaped stress-reducing structure have a smooth transition. When constructing the three types of saddle-shaped shear stress-reducing structures, the top and sides of the saddle-shaped stress-reducing structure must have a smooth transition. That is, the entire area of ​​the curve group or curve grid is an arc, so that the saddle-shaped shear stress structure can effectively reduce the stress level in the high-stress area of ​​the water bucket, and make the stress-reducing area smoothly transition with other areas. By constructing the curve group or curve grid in one go, the step of designing the smooth transition separately is avoided.

[0026] As a preferred embodiment of the present invention, the saddle-shaped stress-reducing structure and the general stress area are bridged by a bridging surface, so that the saddle-shaped stress-reducing structure and the general stress area have a smooth transition.

[0027] The beneficial effects of this invention are as follows:

[0028] 1. This invention artificially divides the root of the water bucket into two parts—a high-stress zone and a general-stress zone—based on the stress distribution at the water bucket root. A saddle-shaped stress-reducing structure with a truncated top is used in the high-stress zone at the water bucket root. This truncated top saddle-shaped stress-reducing structure is equivalent to removing the top of a cylindrical structure, which can effectively reduce the stress level in the high-stress zone of the water bucket.

[0029] 2. A cylindrical surface is constructed in the general stress zone, and then connected to the front and back of the water bucket root by a rounding method with a variable radius, resulting in a simple structure.

[0030] 3. When constructing a saddle-shaped shear stress structure, the top and sides of the saddle-shaped stress-reducing structure must be smoothly transitioned. That is, the entire area of ​​the curve group or curve grid is an arc. This ensures that the saddle-shaped shear stress structure effectively reduces the stress level in the high-stress area of ​​the water bucket and allows the stress-reducing area to smoothly transition with other areas. By constructing the curve group or curve grid in one go, the step of designing a smooth transition separately is avoided.

[0031] 4. The present invention is highly operable and versatile, and can be applied to impulse turbine units of various capacities and heads; its simple design greatly reduces the development cycle of the water bucket. Attached Figure Description

[0032] Figure 1 This is a flowchart of the method of the present invention;

[0033] Figure 2 This is a schematic diagram showing the division of the water bucket base area;

[0034] Figure 3 This is a schematic diagram of a saddle-shaped stress-reducing structure;

[0035] Figure 4 This is a comparison diagram of the traditional cylindrical cross-section in the high-stress zone and the saddle-shaped stress-reducing structure cross-section of the present invention;

[0036] Figure 5 This is a schematic diagram of the bridging water bucket structure;

[0037] Figure 6 This is a flowchart of the traditional method for shaping the base of a water bucket;

[0038] Figure 7 This is a schematic diagram of a water bucket structure using a traditional design. Detailed Implementation

[0039] 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, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0040] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention. It should be noted that, unless otherwise specified, the embodiments and features described in the embodiments of the invention can be combined with each other.

[0041] Example 1:

[0042] like Figures 1-5 As shown, the method for shaping the root of the bucket of an impulse turbine in this embodiment includes the following steps:

[0043] S1: Based on the traditional method of shaping the base of the water bucket, the middle and both sides of the water bucket base are connected by a cylindrical surface transitioning to the curved surface of the water bucket, thus obtaining the basic structure of the water bucket base; the basic structure is as follows: Figure 7 As shown;

[0044] S2: Apply boundary conditions and loads to the water bucket, perform finite element analysis using commercial software, and extract the stress results;

[0045] S3: Based on the stress results, the root of the water bucket is divided into a high-stress zone in the middle and general-stress zones on both sides; the stress zone division is as follows: Figure 2 As shown;

[0046] S4: Add auxiliary sections and control lines in the high-stress area, and construct a saddle-shaped stress-reducing structure with a truncated top using curve groups or curve meshes; the saddle-shaped stress-reducing structure is as follows: Figure 3 and Figure 4 As shown;

[0047] S5: Connected to the front and back sides of the water bucket root through a variable radius rounding method within the general stress zone;

[0048] S6: The saddle-shaped stress-reducing structure is bridged with the general stress zone using a bridging surface, resulting in a smooth transition between the two areas. The bridged water bucket structure is as follows: Figure 5 As shown.

[0049] The method for shaping the root of the impact turbine bucket of the present invention first divides the root area of ​​the bucket into a high-stress area and a general stress area. In the high-stress area, auxiliary sections and control lines are added, and a saddle-shaped stress-reducing structure with a sloping top is constructed by a group of curves or a curve grid. In the general stress area, the bucket root is connected to the front and back sides by a rounding method with a variable radius. Finally, the general stress area and the high-stress area are bridged by a bridging surface to make the various curved surfaces transition smoothly.

[0050] This invention artificially divides the water bucket root into two parts—a high-stress zone and a general stress zone—based on the stress distribution. In the high-stress zone, a saddle-shaped stress-reducing structure with a truncated top is employed. This truncated top structure is equivalent to removing the top of a cylindrical structure, effectively reducing the stress level in the high-stress zone. In the general stress zone, a cylindrical surface is constructed and then connected to the front and back sides of the water bucket root using a rounded design with a variable radius, resulting in a simple structure.

[0051] The present invention is highly operable and versatile, and can be applied to impulse turbine units of various capacities and heads; its simple design greatly reduces the development cycle of the water bucket.

[0052] Specifically, such as Figure 4 As shown, there are three forms of the top-cut saddle-shaped stress-reducing structure.

[0053] The first structural form: The top of the cross-section of the constructed saddle-shaped stress-reducing structure is an upward-convex arc. The curvature of the top of the cross-section of the saddle-shaped stress-reducing structure is greater than the curvature of the top of the cross-section of the cylindrical water bucket root before constructing the saddle-shaped stress-reducing structure. In the first form of saddle-shaped stress-reducing structure, the top of the cross-section of the saddle-shaped stress-reducing structure is an upward-convex arc, but its curvature is larger. Compared with the cylindrical structure, a portion of the structure is still cut off at the top.

[0054] The second structural form: The top of the cross-section of the constructed saddle-shaped stress-reducing structure is a straight line. In this second type of saddle-shaped stress-reducing structure, the top of the cross-section is a straight line, and compared to the cylindrical structure, the second type of saddle-shaped shear stress-reducing structure has its top cut off. The third structural form: The top of the cross-section of the constructed saddle-shaped stress-reducing structure is a downward-concave arc.

[0055] In the third type of saddle-shaped stress-reducing structure, the top of the cross-section of the saddle-shaped stress-reducing structure is a downward-concave arc. Compared with the cylindrical structure, the third type of saddle-shaped shear stress-reducing structure has removed more of the top part.

[0056] It is important to note that when constructing the three types of saddle-shaped shear stress structures, the top and sides of the saddle-shaped stress-reducing structure must be smoothly transitioned. That is, the entire area of ​​the curve group or curve grid should be an arc. This ensures that the saddle-shaped shear stress structure effectively reduces the stress level in the high-stress area of ​​the water bucket and allows the stress-reducing area to smoothly transition with other areas. By constructing the curve group or curve grid in one go, the step of designing a smooth transition separately is avoided.

[0057] Example 2:

[0058] like Figures 2-5 As shown, the bucket root structure of the impulse turbine in this embodiment includes a high-stress zone and a general stress zone. The high-stress zone is a saddle-shaped stress-reducing structure with a sloping top, and the general stress zone is connected to the front and back of the bucket root through a rounded section with a variable radius.

[0059] The division between high-stress and general-stress zones is based on the traditional method of water bucket root design. The middle and sides of the water bucket root are connected by cylindrical surfaces transitioning to the curved surfaces of the water bucket, forming the basic structure of the water bucket root. Boundary conditions and loads are applied to the basic structure of the water bucket root, and finite element analysis is performed using commercial software to extract the stress results. Based on the stress results, the water bucket root is divided into a high-stress zone in the middle and general-stress zones on both sides.

[0060] This invention artificially divides the water bucket root into two parts—a high-stress zone and a general stress zone—based on the stress distribution. The high-stress zone at the water bucket root is a saddle-shaped stress-reducing structure with a truncated top. This truncated top structure is equivalent to removing the top of a cylindrical structure, effectively reducing the stress level in the high-stress zone. A cylindrical surface is constructed in the general stress zone and then connected to the front and back sides of the water bucket root using a rounded design with a variable radius, resulting in a simple structure.

[0061] The top of the cross-section of the saddle-shaped stress-reducing structure is an upwardly convex arc, a straight line, or a downwardly concave arc; when the top of the cross-section of the saddle-shaped stress-reducing structure is an upwardly convex arc, the curvature of the top of the cross-section of the saddle-shaped stress-reducing structure is greater than the curvature of the top of the cross-section of the cylindrical water bucket root before constructing the saddle-shaped stress-reducing structure.

[0062] The top and sides of the saddle-shaped stress-reducing structure have a smooth transition. When constructing the three types of saddle-shaped shear stress-reducing structures, the top and sides of the saddle-shaped stress-reducing structure must have a smooth transition. That is, the entire area of ​​the curve group or curve grid is an arc. In this way, the saddle-shaped shear stress-reducing structure can effectively reduce the stress level in the high-stress area of ​​the water bucket, and make the stress-reducing area smoothly transition with other areas. By constructing the curve group or curve grid in one go, the step of designing the smooth transition separately is avoided.

[0063] In the general stress zone, the structure is connected to the front and back of the water bucket root by a rounded shape with a variable radius. The saddle-shaped stress-reducing structure is bridged with the general stress zone by a bridging surface, resulting in a smooth transition between the two areas.

[0064] This invention is not limited to the above-described optional embodiments. Anyone can derive other various forms of products under the guidance of this invention. However, regardless of any changes made in their shape or structure, any technical solution that falls within the scope of the claims of this invention shall be protected by this invention.

Claims

1. A method of shaping the root of a bucket of an impulse water turbine, characterized by: The method comprises the following steps: The middle part and both sides of the water bucket root are connected with the water bucket curved surface through a cylindrical surface, and a basic structure of the water bucket root is obtained; Boundary conditions and loads are applied to the water bucket, and the water bucket is solved by finite element method, and stress results are extracted; According to the stress results, the water bucket root is divided into a middle high stress area and both sides of a general stress area; An auxiliary section and a control line are added to the high stress area, a saddle-shaped stress reduction structure with a cut top is constructed through a curve group or a curve grid; In the general stress area, a variable radius rounding method is used to connect with the front and back surfaces of the water bucket root; The saddle-shaped stress reduction structure and the general stress area are bridged through a bridging curved surface, so that the saddle-shaped stress reduction structure and the general stress area are smoothly connected.

2. A method of shaping the root of a bucket for a Pelton turbine according to claim 1, characterized in that: The top of the section of the constructed saddle-shaped stress reduction structure with a cut top is an upward convex arc, and the curvature of the top of the section of the saddle-shaped stress reduction structure is greater than the curvature of the top of the section of the cylindrical water bucket root before the saddle-shaped stress reduction structure is constructed.

3. A method of shaping the root of a bucket for an impulse water turbine according to claim 1, characterized in that: The top of the section of the constructed saddle-shaped stress reduction structure with a cut top is a straight line.

4. A method of shaping the root of a bucket for an impulse water turbine according to claim 1, characterized in that: The top of the section of the constructed saddle-shaped stress reduction structure with a cut top is a downward concave arc.

5. A method of shaping the root of a bucket of a Pelton turbine according to any one of claims 2 to 4, characterized in that: The top of the constructed saddle-shaped stress reduction structure is smoothly connected with the side surface.

6. A bucket root structure for a Francis turbine as obtained by the method of claim 1, characterized in that: The high stress area in the middle and the general stress area on both sides, the high stress area is a saddle-shaped stress reduction structure with a cut top, and the general stress area is connected with the front and back surfaces of the water bucket root through a variable radius rounding.

7. A bucket root structure for a pelton turbine according to claim 6, characterized in that: The top of the section of the saddle-shaped stress reduction structure is an upward convex arc or a straight line or a downward concave arc; when the top of the section of the saddle-shaped stress reduction structure is an upward convex arc, the curvature of the top of the section of the saddle-shaped stress reduction structure is greater than the curvature of the top of the section of the cylindrical water bucket root before the saddle-shaped stress reduction structure is constructed.

8. A bucket root structure for a pelton turbine according to claim 6, characterized in that: The top of the saddle-shaped stress reduction structure is smoothly connected with the side surface.

9. A bucket root structure for a pelton turbine according to claim 6, characterized in that: The saddle-shaped stress reduction structure and the general stress area are bridged through a bridging curved surface.

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