Method for estimating fatigue life of runner of wide-load running water turbine

Abstract

The invention discloses a wide-load operation water turbine runner fatigue life estimation method, and belongs to the technical field of water turbine equipment operation and maintenance. In order to accurately predict the fatigue life of the turbine runner, the method comprises the following steps: determining the operation condition of a turbine unit in wide-load operation according to natural conditions and operation requirements of a power station; establishing a finite element model of the water turbine runner, setting boundary conditions of the water turbine runner, loading a pressure field of the water turbine runner, and performing transient analysis and calculation through a finite element method to obtain stress values of the water turbine runner under different operation conditions; extracting the stress amplitude change of the fatigue position of the turbine runner blade; fitting an underwater fatigue life curve through a plurality of test points, and then obtaining the fatigue life of the corresponding position of the turbine runner in wide-load operation based on the underwater fatigue life curve corresponding to the stress amplitude change of the fatigue position of the turbine runner blade. According to the method, the fatigue life of the wide-load running water turbine runner can be estimated more accurately.

Description

Technical Field

[0001] The present invention belongs to the technical field of operation and maintenance of hydroturbine equipment, and particularly relates to a method for predicting the fatigue life of a hydroturbine runner under wide-load operation. Background Art

[0002] At present, conventional hydroturbine units are usually required to operate within a stable load range (60% - 100% output). However, with the progress of hydroelectric unit technology and the change of operating conditions, the operating requirements of the units are gradually increasing, and they need to be able to operate within a wider load range (20% - 100% output), which has an adverse impact on the fatigue life of the runner of the unit. Since the dynamic stress of the runner is difficult to accurately calculate, traditional fatigue life calculation methods usually rely on estimated stress amplitudes and do not fully consider the impact of the switching between different output conditions on fatigue, resulting in a large error in the fatigue life calculated by traditional methods. Therefore, it is urgent to develop a method for predicting the fatigue life of a hydroturbine runner that can adapt to wide-load operating conditions. Summary of the Invention

[0003] The problem to be solved by the present invention is to accurately predict the fatigue life of a hydroturbine runner, and a method for predicting the fatigue life of a hydroturbine runner under wide-load operation is proposed.

[0004] To achieve the above object, the present invention is realized through the following technical solutions:

[0005] A method for predicting the fatigue life of a hydroturbine runner under wide-load operation includes the following steps:

[0006] S1. Determine the operating conditions of the hydroturbine unit operating under wide load according to the natural conditions and operating requirements of the power station;

[0007] S2. Establish a finite element model of the hydroturbine runner, set the boundary conditions of the hydroturbine runner, load the pressure field of the hydroturbine runner, and perform transient analysis and calculation through the finite element method to obtain the stress values of the hydroturbine runner under different operating conditions;

[0008] S3. Based on the stress values of the hydroturbine runner under different operating conditions obtained in step S2, extract the stress amplitude change at the fatigue position of the hydroturbine runner blade;

[0009] S4. Fit the underwater fatigue life curve through multiple test points, and then correspond to the underwater fatigue life curve based on the stress amplitude change at the fatigue position of the hydroturbine runner blade obtained in step S3 to obtain the fatigue life of the corresponding position of the hydroturbine runner under wide-load operation.

[0010] Further, the operating conditions set when the wide - load operating hydro - turbine unit works in step S1 include 20% of the rated power, 40% of the rated power, 60% of the rated power, 80% of the rated power, and 100% of the rated power.

[0011] Further, the specific implementation method of step S2 includes the following steps:

[0012] S2.1. Establish a finite - element model of the hydro - turbine runner, including the crown, blades, lower ring, discharge cone, and bolts for connecting the hydro - turbine runner and the main shaft.

[0013] S2.2. Set the boundary condition of the hydro - turbine runner as fixing the connection between the hydro - turbine runner and the main - shaft bolts, and load the pressure field of the hydro - turbine runner according to the operating conditions of the wide - load operating hydro - turbine unit determined in step S1.

[0014] Under each operating condition, N working points are set for each revolution of the hydro - turbine runner. The rotation angle θ of the hydro - turbine runner model between each working point is θ = 360 / N, and the time interval is t = 60 / N / n, where n is the rated speed of the runner.

[0015] S2.3. Conduct transient analysis through the finite - element method to obtain the stress values of the hydro - turbine runner under different operating conditions. The parameters set for the transient analysis include the damping coefficient, time step, and total number of steps.

[0016] The calculation formula for the damping coefficient is:

[0017]

[0018] where c is a constant, taken as 0.1, f1 is the rotation frequency of the runner, that is f2 is the flow - through frequency of the guide vanes of the runner, that is g is the number of movable guide vanes of the unit.

[0019] Further, the specific implementation method of step S3 includes the following steps:

[0020] S3.1. Set the fatigue positions of the hydro - turbine runner blades, including the intersection of the blade inlet edge and the crown, the intersection of the blade outlet edge and the crown, the intersection of the blade inlet edge and the lower ring, and the intersection of the blade outlet edge and the lower ring.

[0021] S3.2. Based on the stress values σ i ,σ i of the hydro - turbine runner obtained in S2, where σ i are the stress values obtained from the transient analysis of the hydro - turbine runner at different time points, extract the maximum value σ max and the minimum value σ min in σa , the calculation formula is:

[0022]

[0023] Furthermore, the specific implementation method of step S4 includes the following steps:

[0024] S4.1. Fit the underwater fatigue life curve through multiple test points, and the expression of the underwater fatigue life curve is obtained as:

[0025] σ a = 1000G -0.1918

[0026] where G is the allowable number of cycles for the turbine runner under working conditions;

[0027] S4.2. Calculate the fatigue damage coefficient of the turbine runner based on the underwater fatigue life curve obtained in step S4.1;

[0028] S4.2.1. Consider the stress amplitude of fatigue damage caused by unit startup and shutdown where is the maximum stress at the dangerous position of the runner under 100% rated output condition. The allowable number of cycles obtained according to the underwater fatigue curve is G1, the number of unit startup and shutdown is m1, and the fatigue damage coefficient

[0029] S4.2.2. Consider the stress amplitude of fatigue damage caused by runaway condition where is the maximum stress at the dangerous position of the runner under runaway condition. The allowable number of cycles obtained according to the underwater fatigue curve is G2, the number of unit runaway is m2, and the fatigue damage coefficient

[0030] S4.2.3. Consider the stress amplitude of fatigue damage caused by switching between different output conditions where is the maximum stress at the dangerous position of the runner under all different output conditions, is the minimum stress at the dangerous position of the runner under all different output conditions. The allowable number of cycles obtained according to the underwater fatigue curve is G3, the number of times of switching between different output conditions of the unit is m3, and the fatigue damage coefficient

[0031] S4.2.4. Consider the stress amplitude of fatigue damage caused by the fluctuation of the self-pressure field under the same working condition is the maximum stress at the dangerous position of the runner under all the same working conditions, is the minimum stress at the dangerous positions of the runner under all the same operating conditions. The allowable number of cycles obtained according to the underwater fatigue curve is G4, and the number of pressure field fluctuations calculated by the unit according to the rotational speed is m4. The fatigue damage coefficient

[0032] The fatigue damage coefficient S of the water turbine runner is obtained as S = S1 + S2 + S3 + S4, and then the fatigue life of the water turbine runner is estimated as 1 / S.

[0033] Advantages of the present invention:

[0034] For the method for predicting the fatigue life of a water turbine runner with wide-load operation described in the present invention, according to the structural characteristics of the water turbine runner, the most suitable finite element model, reasonable boundary conditions and loading methods for each component are established.

[0035] For the method for predicting the fatigue life of a water turbine runner with wide-load operation described in the present invention, the stress change amplitude generated due to the change of the pressure field and the change of the stress change amplitude during the switching of different output conditions of the water turbine runner under the same operating condition are obtained. When predicting the fatigue life of the water turbine runner, all the situations affecting the fatigue life of the water turbine runner under different operating conditions are fully and accurately considered, and the fatigue life of the water turbine runner with wide-load operation can be more accurately predicted. Description of the drawings

[0036] Figure 1 is the flow chart of the method for predicting the fatigue life of a water turbine runner with wide-load operation described in the present invention;

[0037] Figure 2 is the cross-sectional view of the water turbine runner described in the present invention;

[0038] In the figure, 1 is the crown, 2 is the blade, 3 is the lower ring, 4 is the discharge cone, and 5 is the bolt for coupling the runner and the main shaft. Detailed implementation manners

[0039] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and specific implementation manners. It should be understood that the specific implementation manners described here are only used to explain the present invention and are not used to limit the present invention, that is, the specific implementation manners described are only a part of the implementation manners of the present invention, rather than all the specific implementation manners. Usually, the components of the specific implementation manners of the present invention described and shown in the drawings here can be arranged and designed in various different configurations, and the present invention can also have other implementation manners.

[0040] Accordingly, the following detailed description of the specific embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents selected specific embodiments of the present invention. All other specific embodiments obtained by those skilled in the art based on the specific embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0041] To further understand the content, features and effects of the present invention, the following specific embodiments are exemplified and are described in detail in conjunction with the attached Figure 1 and the attached Figure 2 as follows:

[0042] Embodiment 1:

[0043] A method for predicting the fatigue life of a hydroturbine runner under wide load operation includes the following steps:

[0044] S1. Determine the operating conditions of the hydroturbine unit operating under wide load according to the natural conditions and operating requirements of the power station;

[0045] Further, the operating conditions set when the hydroturbine unit operates under wide load in step S1 include 20% of the rated power, 40% of the rated power, 60% of the rated power, 80% of the rated power, and 100% of the rated power;

[0046] S2. Establish a finite element model of the hydroturbine runner, set the boundary conditions of the hydroturbine runner, load the pressure field of the hydroturbine runner, and perform transient analysis and calculation by the finite element method to obtain the stress values of the hydroturbine runner under different operating conditions;

[0047] Further, the specific implementation method of step S2 includes the following steps:

[0048] S2.1. Establish a finite element model of the hydroturbine runner, including the crown, blades, lower ring, discharge cone, and the bolts for coupling the hydroturbine runner and the main shaft;

[0049] S2.2. Set the boundary conditions of the hydroturbine runner to fix the connection between the hydroturbine runner and the main shaft bolts, and load the pressure field of the hydroturbine runner according to the operating conditions of the hydroturbine unit operating under wide load determined in step S1;

[0050] Under each operating condition, N working points are set for each revolution of the hydroturbine runner. The rotation angle θ of the hydroturbine runner model between each working point is θ = 360 / N, and the time interval is t = 60 / N / n, where n is the rated speed of the runner;

[0051] S2.3. Obtain the stress values of the hydroturbine runner under different operating conditions through transient analysis by the finite element method. The parameters set for the transient analysis include the damping coefficient, time step, and total number of steps;

[0052] The calculation formula for the damping coefficient is:

[0053]

[0054] where c is a constant, taken as 0.1, f1 is the rotation frequency of the runner, i.e., f2 is the flow - through frequency of the guide vanes of the runner, i.e., g is the number of movable guide vanes of the unit.

[0055] S3. Based on the stress values of the water - turbine runner under different operating conditions obtained in step S2, extract the change in the stress amplitude at the fatigue position of the water - turbine runner blades;

[0056] Furthermore, the specific implementation method of step S3 includes the following steps:

[0057] S3.1. Set the fatigue positions of the water - turbine runner blades to include the intersection of the blade inlet edge and the crown, the intersection of the blade outlet edge and the crown, the intersection of the blade inlet edge and the lower ring, and the intersection of the blade outlet edge and the lower ring;

[0058] S3.2. Based on the stress values σ i , σ i of the water - turbine runner obtained in S2, where σ i are the stress values obtained from the transient analysis of the water - turbine runner at different time points, extract the maximum value σ max and the minimum value σ min in σ a , and calculate the stress amplitude σ

[0059]

[0060] S4. Fit the underwater fatigue life curve through multiple test points, and then correspond the change in the stress amplitude at the fatigue position of the water - turbine runner blades obtained in step S3 to the underwater fatigue life curve to obtain the fatigue life at the corresponding position of the water - turbine runner under wide - load operation.

[0061] Furthermore, the specific implementation method of step S4 includes the following steps:

[0062] S4.1. Fit the underwater fatigue life curve through multiple test points to obtain the expression of the underwater fatigue life curve as:

[0063] σ a = 1000G -0.1918

[0064] where G is the allowable number of cycles of the water - turbine runner under the operating condition;

[0065] S4.2. Calculate the fatigue damage coefficient of the turbine runner based on the underwater fatigue life curve obtained in step S4.1;

[0066] S4.2.1. Stress amplitude considering fatigue damage caused by unit startup and shutdown Among them, is the maximum stress at the dangerous position of the runner under the 100% rated

[0067] output condition. The allowable number of cycles obtained according to the underwater fatigue curve is G1, the number of unit startup and shutdown times is m1, and the fatigue damage coefficient

[0068] S4.2.2. Stress amplitude considering fatigue damage caused by runaway condition Among them, is the maximum stress at the dangerous position of the runner under the runaway condition

[0069] The allowable number of cycles obtained according to the underwater fatigue curve is G2, the number of unit runaway times is m2, and the fatigue damage coefficient

[0070] S4.2.3. Stress amplitude considering fatigue damage caused by switching between different output conditions Among them, is the maximum stress at the dangerous position of the runner under all different output conditions, is the runner under all different output conditions

[0071] The minimum stress at the dangerous position. The allowable number of cycles obtained according to the underwater fatigue curve is G3, the number of times of switching between different output conditions of the unit is m3, and the fatigue damage coefficient

[0072] S4.2.4. Stress amplitude considering fatigue damage caused by the fluctuation of its own pressure field under the same condition is the maximum stress at the dangerous position of the runner under all the same conditions, is the runner at the dangerous position under all the same conditions

[0073] The minimum stress. The allowable number of cycles obtained according to the underwater fatigue curve is G4, the number of times of pressure field fluctuation calculated by the unit according to the rotational speed is m4, and the fatigue damage coefficient

[0074] Obtain the fatigue damage coefficient S of the turbine runner as S = S1 + S2 + S3 + S4, and further estimate the fatigue life of the turbine runner as 1 / S.

[0075] It should be noted that relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprising", "including" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements not only includes those elements, but also includes other elements not expressly listed, or elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "comprising an..." does not exclude the existence of additional identical elements in the process, method, article or device comprising the said element.

[0076] Although the present application has been described above with reference to specific embodiments, various improvements can be made thereto and components thereof can be replaced with equivalents without departing from the scope of the present application. In particular, as long as there is no structural conflict, the various features in the specific embodiments disclosed in the present application can be combined with each other in any way, and the exhaustive description of these combinations is not given in this specification only for the sake of saving space and resources. Therefore, the present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A method for predicting the fatigue life of a water turbine runner operating under a wide load range, characterized in that, It includes the following steps: S1. Determine the operating conditions of the hydroturbine unit operating at wide load according to the natural conditions and operating requirements of the power station; S2. Establish a finite element model of the hydroturbine runner, set the boundary conditions of the hydroturbine runner, load the pressure field of the hydroturbine runner, and perform transient analysis and calculation by the finite element method to obtain the stress values of the hydroturbine runner under different operating conditions; S3. Based on the stress values of the hydroturbine runner under different operating conditions obtained in step S2, extract the stress amplitude change at the fatigue position of the hydroturbine runner blades; S4. Fit the underwater fatigue life curve through multiple test points, and then correspond the stress amplitude change at the fatigue position of the hydroturbine runner blades obtained in step S3 to the underwater fatigue life curve to obtain the fatigue life of the corresponding position of the hydroturbine runner operating at wide load.

2. A method for predicting the fatigue life of a wide-load operating water turbine runner according to claim 1, characterized in that, The operating conditions set during the operation of the hydroturbine unit operating at wide load in step S1 include 20% of the rated power, 40% of the rated power, 60% of the rated power, 80% of the rated power, and 100% of the rated power.

3. A method for predicting the fatigue life of a wide-load operating water turbine runner according to claim 1 or 2, characterized in that, The specific implementation method of step S2 includes the following steps: S2.

1. Establish a finite element model of the hydroturbine runner, including the upper crown, blades, lower ring, discharge cone, and the bolts for connecting the hydroturbine runner and the main shaft; S2.

2. Set the boundary condition of the hydroturbine runner to fix the connection between the hydroturbine runner and the main shaft bolts, and load the pressure field of the hydroturbine runner according to the operating conditions of the hydroturbine unit operating at wide load determined in step S1; Under each operating condition, N working condition points are set for each revolution of the hydroturbine runner. The rotation angle θ of the hydroturbine runner model between each working condition point is θ = 360 / N, and the time interval is t = 60 / N / n, where n is the rated speed of the runner; S2.

3. Obtain the stress values of the hydroturbine runner under different operating conditions through transient analysis by the finite element method. The parameters set for the transient analysis include the damping coefficient, time step, and total number of steps; The calculation formula for the damping coefficient is: where c is a constant, taken as 0.1, f1 is the rotation frequency of the runner, that is f2 is the flow - through frequency of the guide vanes of the runner, that is g is the number of movable guide vanes of the unit.

4. A method for predicting the fatigue life of a wide-load operating water turbine runner according to claim 3, characterized in that, The specific implementation method of step S3 includes the following steps: S3.

1. Set the fatigue positions of the hydroturbine runner blades to include the intersection of the blade inlet edge and the upper crown, the intersection of the blade outlet edge and the upper crown, the intersection of the blade inlet edge and the lower ring, and the intersection of the blade outlet edge and the lower ring; S3.

2. Based on the stress value σ of the turbine runner under different operating conditions obtained in S2 i , σ i is the stress value obtained from the transient analysis of the turbine runner at different time points. Extract the maximum value σ i and the minimum value σ max in it, and calculate the stress amplitude σ min at the fatigue position of the blade. The calculation formula is: a The calculation formula is:

5. A method for predicting the fatigue life of a wide-load operating water turbine runner according to claim 4, characterized in that The specific implementation method of step S4 includes the following steps: S4.

1. Fit the underwater fatigue life curve through multiple test points, and the expression of the underwater fatigue life curve is: σ a = 1000 G -0.1918 where G is the allowable number of cycles of the hydroturbine runner working condition; S4.

2. Calculate the fatigue damage coefficient of the hydroturbine runner based on the underwater fatigue life curve obtained in step S4.1; S4.2.

1. Stress amplitude considering fatigue damage caused by unit startup and shutdown Among them, is the maximum stress at the dangerous position of the runner under the condition of 100% rated output. The allowable number of cycles obtained according to the underwater fatigue curve is G1, the number of unit startup and shutdown is m1, and the fatigue damage coefficient S4.2.

2. Stress amplitude considering fatigue damage caused by runaway condition where is the maximum stress at the dangerous position of the runner under runaway condition. The allowable number of cycles obtained from the underwater fatigue curve is G2, the number of runaway times of the unit is m2, and the fatigue damage coefficient S4.2.

3. Consider the stress amplitude of fatigue damage caused by the switching between different output conditions Among them, is the maximum stress at the dangerous position of the runner under all different output conditions, is the minimum stress at the dangerous position of the runner under all different output conditions. The allowable number of cycles obtained from the underwater fatigue curve is G3, the number of switching times between different output conditions of the unit is m3, and the fatigue damage coefficient S4.2.

4. Consider the stress amplitude of fatigue damage caused by the fluctuation of its own pressure field under the same working condition is the maximum stress at the dangerous positions of the runner under all the same working conditions, is the minimum stress at the dangerous positions of the runner under all the same working conditions. The allowable number of cycles obtained according to the underwater fatigue curve is G4, and the number of pressure field fluctuations calculated by the unit according to the rotational speed is m4. The fatigue damage coefficient Obtain the fatigue damage coefficient S of the hydroturbine runner as S = S1 + S2 + S3 + S4, and further estimate the fatigue life of the hydroturbine runner as 1 / S.

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