Method and structure for adjusting inherent frequency of pelton turbine bucket

Abstract

The present application belongs to the technical field of water turbine, and particularly relates to a method and structure for adjusting inherent frequency of a bucket of an impulse water turbine. The method comprises the following steps: according to the CFD calculation result, partitioning the back of the bucket, and determining the area affecting water power and the area not affecting water power; using a bucket root shaping method, establishing a three-dimensional model of the bucket; in the area not affecting water power, adding auxiliary lines and auxiliary surfaces, and constructing a frequency adjustment module through a stitching command; building a finite element model, applying boundary conditions, and solving; cyclically performing the following steps: extracting each section diameter mode under a torsional vibration mode and the corresponding inherent frequency, and comparing with the corresponding mode excitation frequency to determine whether resonance occurs; if resonance occurs, determining and deciding the adjustment direction, such as thickening the frequency adjustment module if the inherent frequency needs to be increased, or thinning the frequency adjustment module if the inherent frequency needs to be decreased; and determining the optimal thickness of the frequency adjustment module. The present application provides a simple and fast method and structure for adjusting inherent frequency of a bucket of an impulse water turbine.

Description

Technical Field

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

[0002] Unlike reaction turbines, the bucket rotates at high speed in the air. If the bucket breaks, it threatens the lives of power plant maintenance personnel and seriously affects the safety and stability of the impulse turbine operation. Therefore, in the research and design of the bucket, in addition to considering operational efficiency, it is also necessary to adjust the bucket's natural frequencies so that the natural frequencies corresponding to the various pitch diameter modes of its torsional vibration mode completely avoid the excitation frequencies of their respective modes, thus ensuring that resonance will never occur.

[0003] Currently, in the design of impulse turbine bucket structures, there is no rapid method for adjusting the natural frequencies of the buckets. Instead, after the bucket root structure is completed, commercial software is used to calculate its natural frequencies and compare them with its excitation frequency to check for resonance. If resonance occurs, the bucket must be redesigned, which greatly increases the difficulty of bucket research and development and prolongs the research and development cycle. Summary of the Invention

[0004] In order to solve the above-mentioned problems in the prior art, the purpose of this invention is to provide a simple and quick method and structure for adjusting the natural frequency of the bucket of an impulse turbine.

[0005] The technical solution adopted in this invention is as follows:

[0006] A method for adjusting the natural frequency of the bucket of an impulse turbine includes the following steps:

[0007] Based on the CFD calculation results, the back of the water tank is divided into zones to clearly define the areas that affect hydraulics and the areas that do not.

[0008] A three-dimensional model of the water hopper was established using the water hopper root modeling method.

[0009] In areas where hydraulics are not affected, add auxiliary lines and surfaces, and construct a frequency modulation module using the stitching command;

[0010] Build a finite element model, apply boundary conditions, and solve for the solution.

[0011] The process is repeated: extract each pitch diameter mode and its corresponding natural frequency under torsional vibration mode, and compare it with the excitation frequency of the corresponding mode to determine whether resonance occurs; if resonance occurs, determine and decide the adjustment direction. If the natural frequency needs to be increased, thicken the frequency tuning module; if the natural frequency needs to be decreased, thin the frequency tuning module.

[0012] Determine the optimal thickness of the frequency modulation module.

[0013] This invention, based on CFD calculations, divides the back of the water bucket into zones to identify which areas affect hydraulics and which do not. A three-dimensional model of the water bucket is established using a root-modeling method. In areas where hydraulics are not affected, auxiliary lines and surfaces are added, and a frequency tuning module is constructed using a stitching command, smoothly transitioning to the root using a bridging surface. A finite element model is built using commercial software, boundary conditions are applied, and the model is solved. The modes of each pitch diameter under torsional vibration and their corresponding natural frequencies are extracted and compared with the excitation frequencies of the corresponding modes to determine if resonance occurs. If resonance occurs, the adjustment direction is determined; for example, to increase the natural frequency, the frequency tuning module is thickened, and vice versa. This process is repeated several times to determine the optimal thickness of the frequency tuning module.

[0014] This invention enables simple and rapid adjustment of the natural frequency of the water turbine, ensuring that the natural frequency of its modes avoids the excitation frequency of the corresponding modes to the greatest extent possible during the design phase, thereby guaranteeing the safe and stable operation of the unit. This invention only adjusts the frequency modulation module, reducing the difficulty of water turbine development and shortening the development cycle.

[0015] As a preferred embodiment of the present invention, when constructing the frequency modulation module, the frequency modulation module and the root of the water bucket are smoothly transitioned through a bridging curved surface.

[0016] As a preferred embodiment of the present invention, the area that affects the hydraulic power is the outer side of the water bucket, and the area that does not affect the hydraulic power is the side of the back of the water bucket near the hub of the impeller.

[0017] An impulse turbine bucket inherent frequency adjustment structure includes a frequency adjustment module located in the bucket area that does not affect hydraulic operation.

[0018] This invention, by placing a frequency modulation module in the water bucket in a region that does not affect hydraulic operation, ensures that the natural frequencies of its modes avoid the excitation frequencies of the corresponding modes to the greatest extent possible during the design phase, thereby guaranteeing the safe and stable operation of the unit. During the adjustment of the water bucket's own natural frequencies, only the frequency modulation module needs to be adjusted, reducing the difficulty and shortening the development cycle of the water bucket.

[0019] As a preferred embodiment of the present invention, the frequency modulation module smoothly transitions to the root of the water bucket.

[0020] As a preferred embodiment of the present invention, the area where the water bucket does not affect the hydraulic system is the side of the back of the water bucket near the hub of the impeller.

[0021] The beneficial effects of this invention are as follows:

[0022] This invention enables simple and rapid adjustment of the natural frequency of the water turbine, ensuring that the natural frequency of its modes avoids the excitation frequency of the corresponding modes to the greatest extent possible during the design phase, thereby guaranteeing the safe and stable operation of the unit. This invention only adjusts the frequency modulation module, reducing the difficulty of water turbine development and shortening the development cycle. Attached Figure Description

[0023] Figure 1 This is a flowchart of the method of the present invention;

[0024] Figure 2 This is a schematic diagram of the partitions on the back of the water tank;

[0025] Figure 3 This is a schematic diagram of a water bucket structure with a frequency modulation module. Detailed Implementation

[0026] 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.

[0027] 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.

[0028] Example 1:

[0029] like Figures 1-3 As shown, the method for adjusting the natural frequency of the bucket of an impulse turbine in this embodiment includes the following steps:

[0030] S1: Based on the CFD calculation results, the back of the water tank is divided into zones to clearly define the areas that affect hydraulics and the areas that do not affect hydraulics;

[0031] S2: Using the water bucket root modeling method, a three-dimensional model of the water bucket is established;

[0032] S3: In the area that does not affect the hydraulics, add auxiliary lines and auxiliary surfaces, construct the frequency tuning module using the stitching command, and smoothly transition it with the root using a bridging surface.

[0033] S4: Use commercial software to build a finite element model, apply boundary conditions, and solve the problem;

[0034] S5: Extract each pitch diameter mode and its corresponding natural frequency under torsional vibration mode, and compare it with the excitation frequency of the corresponding mode to determine whether resonance occurs;

[0035] S6: If resonance occurs, determine and decide on the adjustment direction. If the natural frequency needs to be increased, thicken the frequency modulation module; if the natural frequency needs to be decreased, thin the frequency modulation module. Repeat this process several times to determine the optimal thickness of the frequency modulation module.

[0036] This invention, based on CFD calculations, divides the back of the water bucket into zones to identify which areas affect hydraulics and which do not. A three-dimensional model of the water bucket is established using a root-modeling method. In areas where hydraulics are not affected, auxiliary lines and surfaces are added, and a frequency tuning module is constructed using a stitching command, smoothly transitioning to the root using a bridging surface. A finite element model is built using commercial software, boundary conditions are applied, and the model is solved. The modes of each pitch diameter under torsional vibration and their corresponding natural frequencies are extracted and compared with the excitation frequencies of the corresponding modes to determine if resonance occurs. If resonance occurs, the adjustment direction is determined; for example, to increase the natural frequency, the frequency tuning module is thickened, and vice versa. This process is repeated several times to determine the optimal thickness of the frequency tuning module.

[0037] This invention enables simple and rapid adjustment of the natural frequency of the water turbine, ensuring that the natural frequency of its modes avoids the excitation frequency of the corresponding modes to the greatest extent possible during the design phase, thereby guaranteeing the safe and stable operation of the unit. This invention only adjusts the frequency modulation module, reducing the difficulty of water turbine development and shortening the development cycle.

[0038] The area that affects the hydraulic power is the outer side of the bucket, while the area that does not affect the hydraulic power is the middle area on the back of the bucket near the wheel hub.

[0039] Example 2:

[0040] The impulse turbine bucket inherent frequency adjustment structure of this embodiment includes a frequency tuning module disposed in the area of ​​the bucket that does not affect hydraulic operation. The frequency tuning module smoothly transitions to the root of the bucket. The area of ​​the bucket that does not affect hydraulic operation is the middle region on the back of the bucket near the runner hub.

[0041] This invention, by placing a frequency modulation module in the water bucket in a region that does not affect hydraulic operation, ensures that the natural frequencies of its modes avoid the excitation frequencies of the corresponding modes to the greatest extent possible during the design phase, thereby guaranteeing the safe and stable operation of the unit. During the adjustment of the water bucket's own natural frequencies, only the frequency modulation module needs to be adjusted, reducing the difficulty and shortening the development cycle of the water bucket.

[0042] 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 for adjusting the natural frequency of the bucket of an impulse turbine, characterized in that: Includes the following steps: Based on the CFD calculation results, the back of the water tank is divided into zones to clearly define the areas that affect hydraulics and the areas that do not. A three-dimensional model of the water hopper was established using the water hopper root modeling method. In areas where hydraulics are not affected, add auxiliary lines and surfaces, and construct a frequency modulation module using the stitching command; Build a finite element model, apply boundary conditions, and solve for the solution. The process is repeated: extract each pitch diameter mode and its corresponding natural frequency under torsional vibration mode, and compare it with the excitation frequency of the corresponding mode to determine whether resonance occurs; if resonance occurs, determine and decide the adjustment direction. If the natural frequency needs to be increased, thicken the frequency tuning module; if the natural frequency needs to be decreased, thin the frequency tuning module. Determine the optimal thickness of the frequency modulation module.

2. The method for adjusting the natural frequency of the bucket of an impulse turbine according to claim 1, characterized in that: When constructing the frequency modulation module, ensure a smooth transition between the frequency modulation module and the water bucket root using a bridging curved surface.

3. The method for adjusting the natural frequency of the bucket of an impulse turbine according to claim 1, characterized in that: The area that affects the hydraulic power is the outer side of the bucket, while the area that does not affect the hydraulic power is the back of the bucket near the wheel hub.

4. A bucket natural frequency adjustment structure for an impulse turbine obtained by the method described in claim 1, characterized in that: This includes a frequency modulation module located in the water tank area that does not affect the hydraulic system.

5. The impulse turbine bucket natural frequency adjustment structure according to claim 4, characterized in that: The frequency modulation module smoothly transitions into the root of the water bucket.

6. The impulse turbine bucket natural frequency adjustment structure according to claim 4, characterized in that: The area where the water bucket does not affect hydraulic power is the back of the water bucket on the side near the wheel hub.

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