Runner blade modification method and system for improving stress concentration

Abstract

The invention discloses a runner blade modification method and system for improving stress concentration, and the method comprises the steps: constructing a three-dimensional model of a turbine runner, projecting the roots, connected with an upper crown and a lower ring, of a runner blade on an equal-span plane, and drawing an airfoil skeleton line; based on the starting point and the ending point of the airfoil profile bone line, the percentage of the length of the runner blade at the root of the blade in the direction from the water inlet edge to the water outlet edge in the total length is defined as a relative spatial position s, and the positions of an airfoil profile reducing control point, a water inlet edge starting point and a water outlet edge ending point are determined; restoring an airfoil variable-diameter control point to the original runner blade by using an inverse projection method, and performing chamfering thickening treatment on the root part of the connecting upper crown and the lower ring of the blade according to a variable-diameter chamfering formula and a chamfering variable-diameter rule; a runner blade stress distribution value is obtained through fluid-solid coupling analysis, and runner blade remodeling is completed. While the efficiency is considered, the stress concentration of the blades is improved, and the service life of the rotating wheel is greatly prolonged.

Description

Technical Field

[0001] The invention relates to the technical field of turbine runner blades, and in particular to a runner blade modification method and system for improving stress concentration. Background Art

[0002] The main function of the Francis turbine is to convert water energy into mechanical energy, and then into electrical energy through a generator. It has the characteristics of compact structure, high efficiency, and wide range of water head. It is one of the turbine types widely used in countries around the world. The wide application of this turbine has played an important role in promoting the rapid development of the hydropower industry.

[0003] The runner is the most important flow-passing component of the turbine. It guides the water flow and is also subjected to alternating stress loads. The runner consists of an upper crown, a lower ring and blades. The upper crown and the lower ring are the fixed parts of the runner, and together with the blades, they constitute the overall structure of the runner. At present, the optimization design of runner blades mainly focuses on improving their efficiency, reducing pressure pulsation, avoiding resonance, and adapting to multiple working conditions, but few consider improving the stress concentration of runner blades. Due to the constraints of the runner structure design, various hydraulic excitation factors will induce vibrations and generate alternating stresses. Stress concentration will occur at the contact surface between the blade root and the upper crown and the lower ring. This requires optimizing the blade design to improve its load distribution to improve the efficiency and stability of the runner. This is also the top priority for studying the flow field inside the turbine and optimizing the turbine design, and has an important impact on the hydraulic performance of the turbine. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a method and system for modifying the runner blades for improving stress concentration, optimizing the chamfering and local thickening of the root of the blades connecting the upper crown and the lower ring of the runner to increase the strength of the runner blades, and being able to effectively improve the stress concentration of the runner blades in the working state while ensuring efficiency, thereby greatly increasing the life of the runner.

[0005] In order to solve the above technical problems, the present invention provides a runner blade modification method for improving stress concentration, comprising the following steps:

[0006] S1. Construct a three-dimensional model of the turbine runner, project the root of the runner blade connecting the upper crown and the lower ring onto an equal span plane, unfold it to a two-dimensional plane to obtain the airfoil of the plane cascade, calculate the airfoil blade length, and draw the airfoil bone line.

[0007] S2. Based on the starting and ending points of the airfoil bone line obtained in step S1, define the percentage of the length from the water inlet edge to the water outlet edge of the runner blade at the root of the blade as the relative spatial position s, and then determine the positions of the airfoil variable diameter control point, the starting point of the water inlet edge, and the ending point of the water outlet edge.

[0008] S3, using the reverse projection method to restore the airfoil variable diameter control point in step S2 to the original runner blade, and chamfering and thickening the root of the blade where the upper crown and the lower ring are connected according to the variable diameter chamfer formula and the chamfer variable diameter rule;

[0009] S4. Based on computational fluid dynamics (CFD), the result obtained after processing in step S3 is calculated, and the stress distribution value of the runner blade is obtained through fluid-solid coupling analysis, so as to complete the modification of the runner blade.

[0010] Furthermore, in step S1, the upper crown, blades and lower ring of the water turbine are modeled according to the structural dimensions of the water turbine to obtain a three-dimensional model of the water turbine runner.

[0011] The calculation formula of airfoil blade length is:

[0012] f=σ×t

[0013] Among them, f represents the airfoil blade length, t represents the blade distance, and σ represents the blade density.

[0014] The midline of the cross-sectional shape of the blade along the streamline direction is the airfoil bone line.

[0015] Further, in step S2, the point at s=0.5 on the root of the runner blade connecting the upper crown and the lower ring is the airfoil variable diameter control point E, the point at s=0 is the starting point P0 of the water inlet edge, and the point at s=1 is the ending point P1 of the water outlet edge.

[0016] Furthermore, in step S3, the radius of the chamfer is obtained using the variable diameter chamfer formula, and the specific formula is:

[0017]

[0018] Among them, R1(s) represents the radius of the variable chamfer between the root of the blade and the upper crown, R2(s) represents the radius of the variable chamfer between the root of the blade and the lower ring, D1 represents the upper crown diameter of the turbine runner, and D2 represents the lower ring diameter of the turbine runner.

[0019] Based on the radius of the chamfer, the chamfer reduction rule is used to chamfer and thicken the root of the blade where the upper crown and the lower ring are connected. Specifically:

[0020] The chamfer radii at the starting point of the water inlet edge of the root where the blade connects the upper crown and the lower ring are a1 and a2 respectively. The relative spatial position between the starting point of the water inlet edge and the airfoil variable diameter control point is a variable diameter chamfer that changes based on the variable diameter chamfer formula. The chamfers at the relative spatial position between the airfoil variable diameter control point and the ending point of the water outlet edge of the root where the blade connects the upper crown and the lower ring are uniform chamfers of b1 and b2 respectively.

[0021] Furthermore, a1=0.00578D1, a2=0.00386D2, b1=0.000263D1, b2=0.000834D2.

[0022] Furthermore, the present invention also proposes a runner blade modification system for improving stress concentration, comprising:

[0023] The airfoil bone line drawing module is used to construct a three-dimensional model of the turbine runner, project the root of the runner blade connecting the upper crown and the lower ring onto an equal span plane, and unfold it to a two-dimensional plane to obtain the airfoil of the plane blade cascade, calculate the airfoil blade length, and draw the airfoil bone line.

[0024] The key point determination module is used to define the percentage of the length from the water inlet edge to the water outlet edge of the runner blade at the root of the blade as the percentage of the total length based on the starting and ending points of the airfoil bone line, and then determine the positions of the airfoil variable diameter control point, the starting point of the water inlet edge and the ending point of the water outlet edge.

[0025] The chamfering and thickening processing module is used to restore the airfoil variable diameter control point to the original runner blade by using the reverse projection method, and to perform chamfering and thickening processing on the root of the blade connecting the upper crown and the lower ring according to the variable diameter chamfering formula and the chamfering variable diameter rule.

[0026] The runner blade modification module is used to calculate the results of chamfer thickening treatment based on computational fluid dynamics, obtain the stress distribution value of the runner blade through fluid-solid coupling analysis, and complete the modification of the runner blade.

[0027] Furthermore, the present invention also proposes an electronic device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the steps of the above-mentioned method for modifying the runner blades to improve stress concentration when executing the computer program.

[0028] Furthermore, the present invention also proposes a computer-readable storage medium, wherein the computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the runner blade modification method for improving stress concentration described above is executed.

[0029] Compared with the prior art, the present invention adopts the above technical solution and has the following technical effects:

[0030] 1. The present invention broadens the application scope of turbine runner design, and proposes an optimization method for effectively improving the stress concentration of turbine runner blades through a large amount of theoretical analysis and numerical simulation verification.

[0031] 2. The present invention can select appropriate variable chamfer radii between the blade root, the upper crown and the lower ring and the relative spatial position numerical parameter s from the water inlet edge to the water outlet edge of the runner blade at the blade root according to different mixed flow turbines, so as to achieve the purpose of improving the blade stress concentration while taking into account the efficiency, thereby greatly improving the life of the runner. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a structural diagram of a runner of the present invention.

[0033] Figure 2 It is a structural diagram of the blade chamfer of the present invention.

[0034] Figure 3 It is a chamfer design drawing of the blade diameter change control point of the present invention.

[0035] Figure 4 It is the chamfer distribution diagram along the blade surface of the present invention.

[0036] Figure numerals: 1 - upper crown; 2 - blade; 3 - lower ring; 4 - contact surface between blade root and upper crown; 5 - contact surface between blade root and lower ring. DETAILED DESCRIPTION

[0037] The present invention will be further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and cannot be used to limit the protection scope of the present invention.

[0038] In conventional turbine designs, stress concentration occurs at the contact surface between the root of the runner blade and the upper crown and lower ring. After in-depth research on the blades of the turbine runner, it was found through a large number of numerical simulations that thickening the contact surface between the root of the runner blade and the upper crown and lower ring with a large chamfer on the water inlet side and a small chamfer on the water outlet side can effectively improve the phenomenon of stress concentration. The method of local thickening of the chamfer of the variable diameter control point adopted in the present invention can achieve the effect of improving stress concentration while taking into account efficiency.

[0039] To achieve the above object, the present invention proposes a runner blade modification method for improving stress concentration, and the specific steps are as follows:

[0040] S1. Construct a three-dimensional model of the turbine runner, project the root of the runner blade connecting the upper crown and the lower ring onto the equal span plane, and unfold it to a two-dimensional plane to obtain the airfoil of the plane cascade, calculate the airfoil blade length, and draw the airfoil bone line. The specific contents are:

[0041] According to the structural dimensions of the turbine, the upper crown, blades and lower ring of the turbine are modeled to obtain a three-dimensional model of the turbine runner;

[0042] The calculation formula of airfoil blade length is:

[0043] f=σ×t

[0044] Where f represents the airfoil blade length, t represents the blade distance, and σ represents the blade density;

[0045] The midline of the cross-sectional shape of the blade along the streamline direction is the airfoil bone line.

[0046] In this embodiment, a certain Francis turbine is taken as the object for design optimization. Figure 1 The specific basic parameters are shown in Table 1.

[0047] Table 1 Parameters of Francis turbine

[0048]

[0049]

[0050] S2. Based on the starting and ending points of the airfoil bone line obtained in step S1, define the percentage of the length of the runner blade from the water inlet edge to the water outlet edge at the root of the blade as the relative spatial position s, and then determine the positions of the airfoil variable diameter control point, the water inlet edge starting point and the water outlet edge ending point. The point at s=0.5 on the root of the runner blade connecting the upper crown and the lower ring is the airfoil variable diameter control point E, the point at s=0 is the water inlet edge starting point P0, and the point at s=1 is the water outlet edge ending point P1.

[0051] S3, using the reverse projection method to restore the airfoil variable diameter control point in step S2 to the original runner blade, and chamfering and thickening the root of the blade connecting the upper crown and the lower ring according to the variable diameter chamfer formula and the chamfer variable diameter rule. The specific contents are:

[0052] The radius of the chamfer is obtained by using the variable diameter chamfer formula. The specific formula is:

[0053]

[0054] Among them, R1(s) represents the radius of the variable chamfer between the root of the blade and the upper crown, R2(s) represents the radius of the variable chamfer between the root of the blade and the lower ring, R1(s) and R2(s) are both positive numbers (unit: mm), 0≤s≤0.5, D1 represents the upper crown diameter of the turbine runner, and D2 represents the lower ring diameter of the turbine runner.

[0055] Based on the radius of the chamfer, the chamfer reduction rule is used to chamfer and thicken the root of the blade where the upper crown and the lower ring are connected. Specifically:

[0056] The chamfer radii at the starting point of the water inlet edge of the root where the blade connects the upper crown and the lower ring are a1 and a2 respectively. The relative spatial position between the starting point of the water inlet edge and the airfoil variable diameter control point is a variable diameter chamfer that changes based on the variable diameter chamfer formula. The chamfers at the relative spatial position between the airfoil variable diameter control point and the ending point of the water outlet edge of the root where the blade connects the upper crown and the lower ring are uniform chamfers of b1 and b2 respectively.

[0057] a1=0.00578D1, a2=0.00386D2, b1=0.000263D1, b2=0.000834D2.

[0058] S4. Calculate the result processed in step S3 based on CFD (Computational Fluid Dynamics), obtain the stress distribution value of the runner blade through fluid-solid coupling analysis, and complete the modification of the runner blade.

[0059] In this embodiment, three models with different thickening methods are proposed for comparison with the existing model:

[0060] Add chamfers to existing models. The chamfer structure is as follows: Figure 2 As shown, the chamfer thickening treatment method of model AC is as follows Figure 3 The chamfer distribution diagram is shown in Figure 4 As shown:

[0061] Model A: The chamfer radius of the water inlet and outlet edges at the root of the blade connecting the upper crown and the lower ring is a mm, and the chamfer radius from the water inlet to the outlet edge of the blade root changes uniformly.

[0062] Model B: The chamfer radius of the water inlet edge of the root where the blade connects the upper crown and the lower ring is amm, the chamfer radius of the water outlet edge of the root where the blade connects the upper crown and the lower ring is bmm, and the chamfer radius from the water inlet edge to the water outlet edge of the blade root changes linearly;

[0063] Model C: The chamfer radius at the starting point of the water inlet edge at the root where the blade connects the upper crown and the lower ring is amm, the chamfer radius at the ending point of the water outlet edge at the root where the blade connects the upper crown and the lower ring is bmm, the relative spatial position between the starting point of the water inlet edge at the root of the blade and the variable diameter control point E is a variable diameter chamfer based on the variable diameter chamfer formula, and the chamfer at the relative spatial position between the variable diameter control point E and the ending point of the water outlet edge is a uniform chamfer with a radius of bmm. This is a method for local thickening of the chamfer at the variable diameter control point.

[0064] Based on CFD, four models were simulated and calculated, and the maximum head and full opening conditions were selected as the verification conditions. After no less than three calculations, the experimental data results of efficiency and stress were obtained as shown in Table 2.

[0065] Table 2 Comparison of efficiency and stress values ​​of four models

[0066] parameter Existing Models Model A Model B Model C Efficiency η(%) 93.47 92.05 92.39 93.41 Maximum stress value σ(MPa) 145.61 101.92 103.14 102.55

[0067] It can be seen that compared with the existing models, model C achieves the effect of improving stress concentration while taking into account efficiency, while models A and B achieve the effect of improving stress concentration but the efficiency value is reduced by about 1%.

[0068] The embodiment of the present invention also proposes a runner blade modification system for improving stress concentration, including an airfoil bone line drawing module, a key point determination module, a chamfer thickening processing module, a runner blade modification module, and a computer program that can be run on a processor. It should be noted that each module in the above system corresponds to the specific steps of the method provided in the embodiment of the present invention, and has the corresponding functional modules and beneficial effects of the execution method. For technical details not described in detail in this embodiment, please refer to the method provided in the embodiment of the present invention.

[0069] The embodiment of the present invention further provides an electronic device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor. It should be noted that when the processor executes the computer program, the specific steps of the method provided in the embodiment of the present invention are corresponding to the specific steps of the method provided in the embodiment of the present invention, and the processor has the functional modules and beneficial effects corresponding to the execution method. For technical details not described in detail in this embodiment, please refer to the method provided in the embodiment of the present invention.

[0070] The embodiment of the present invention further provides a computer-readable storage medium, wherein the computer-readable storage medium stores a computer program. It should be noted that when the computer program is executed by the processor, it corresponds to the specific steps of the method provided in the embodiment of the present invention, and has the functional modules and beneficial effects corresponding to the execution method. For technical details not described in detail in this embodiment, please refer to the method provided in the embodiment of the present invention.

[0071] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A runner blade modification method for improving stress concentration, characterized in that: include: S1. Construct a three-dimensional model of a turbine runner, project the root of the runner blade connecting the upper crown and the lower ring onto a plane of equal span, unfold it onto a two-dimensional plane to obtain the airfoil of the plane cascade, calculate the airfoil blade length, and draw the airfoil bone line; S2, based on the starting and ending points of the airfoil bone line obtained in step S1, define the percentage of the length of the runner blade from the water inlet edge to the water outlet edge at the blade root to the total length as the relative spatial position s, and then determine the positions of the airfoil variable diameter control point, the water inlet edge starting point, and the water outlet edge ending point; S3, using the reverse projection method to restore the airfoil variable diameter control point in step S2 to the original runner blade, and chamfering and thickening the root of the blade where the upper crown and the lower ring are connected according to the variable diameter chamfer formula and the chamfer variable diameter rule; S4. Calculate the result processed in step S3 based on computational fluid dynamics, obtain the stress distribution value of the runner blade through fluid-solid coupling analysis, and complete the modification of the runner blade.

2. The runner blade modification method for improving stress concentration according to claim 1, characterized in that: In step S1, the upper crown, blades and lower ring of the water turbine are modeled according to the structural dimensions of the water turbine to obtain a three-dimensional model of the water turbine runner; The calculation formula of airfoil blade length is: f=σ×t Where f represents the airfoil blade length, t represents the blade distance, and σ represents the blade density; The midline of the cross-sectional shape of the blade along the streamline direction is the airfoil bone line.

3. The runner blade modification method for improving stress concentration according to claim 1, characterized in that: In step S2, the point at s=0.5 on the root of the runner blade connecting the upper crown and the lower ring is the airfoil variable diameter control point E, the point at s=0 is the starting point P0 of the water inlet edge, and the point at s=1 is the ending point P1 of the water outlet edge.

4. The runner blade modification method for improving stress concentration according to claim 1, characterized in that: In step S3, the radius of the chamfer is obtained using the variable diameter chamfer formula, and the specific formula is: Wherein, R1(s) represents the radius of the variable chamfer between the blade root and the upper crown, R2(s) represents the radius of the variable chamfer between the blade root and the lower ring, D1 represents the upper crown diameter of the turbine runner, and D2 represents the lower ring diameter of the turbine runner; Based on the radius of the chamfer, the chamfer reduction rule is used to chamfer and thicken the root of the blade where the upper crown and the lower ring are connected. Specifically: The chamfer radii at the starting point of the water inlet edge of the root where the blade connects the upper crown and the lower ring are a1 and a2 respectively. The relative spatial position between the starting point of the water inlet edge and the airfoil variable diameter control point is a variable diameter chamfer that changes based on the variable diameter chamfer formula. The chamfers at the relative spatial position between the airfoil variable diameter control point and the ending point of the water outlet edge of the root where the blade connects the upper crown and the lower ring are uniform chamfers of b1 and b2 respectively.

5. The runner blade modification method for improving stress concentration according to claim 4, characterized in that: a1=0.00578D1, a2=0.00386D2, b1=0.000263D1, b2=0.000834D2.

6. A system for the runner blade modification method for improving stress concentration according to claim 1, characterized in that: include: The airfoil bone line drawing module is used to construct a three-dimensional model of the turbine runner, project the root of the runner blade connecting the upper crown and the lower ring onto the equal span plane, and unfold it to a two-dimensional plane to obtain the airfoil of the plane cascade, calculate the airfoil blade length, and draw the airfoil bone line; The key point determination module is used to define the percentage of the length of the runner blade from the water inlet edge to the water outlet edge at the root of the blade to the total length as the relative spatial position s based on the starting and ending points of the airfoil bone line, and then determine the positions of the airfoil variable diameter control point, the starting point of the water inlet edge and the ending point of the water outlet edge; The chamfering and thickening processing module is used to restore the airfoil variable diameter control point to the original runner blade by using the reverse projection method, and to perform chamfering and thickening processing on the root of the blade connecting the upper crown and the lower ring according to the variable diameter chamfering formula and the chamfering and variable diameter rule; The runner blade modification module is used to calculate the results of chamfer thickening treatment based on computational fluid dynamics, obtain the stress distribution value of the runner blade through fluid-solid coupling analysis, and complete the modification of the runner blade.

7. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the computer program, the steps of the runner blade modification method for improving stress concentration according to any one of claims 1 to 5 are implemented.

8. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, the runner blade modification method for improving stress concentration according to any one of claims 1 to 5 is performed.

Images