Impact turbine runner wet mode numerical simulation method

Abstract

The invention relates to the technical field of impulse turbines, in particular to an impulse turbine runner wet mode numerical simulation method, which comprises the following steps of: establishing an impulse turbine fluid numerical simulation model comprising a water distribution ring pipe, a direct flow spray pipe and a runner position water body, and defining pretreatment setting comprising a turbulence model, a wall surface function and a boundary condition; solving to obtain the distribution state of the fluid near the runner bucket of the impulse turbine along with the time change; based on a calculation result, selecting a plurality of typical distribution states as wet modal calculation working condition points of the impact type rotating wheel; fluid units corresponding to modal calculation working condition points are extracted from the fluid analysis model and transferred to a wet modal analysis model; combining the obtained fluid unit and the runner structure unit to establish a complete impact type runner wet modal analysis model; defining boundary conditions including structural model freedom degree constraint, fluid model surface constraint and structure and fluid fluid-solid coupling effect; and solving and extracting the wet modal analysis result of the impact runner to obtain the key vibration mode and the corresponding inherent frequency of the runner. According to the method, the key vibration mode and the corresponding inherent frequency of the impulse turbine runner can be obtained by utilizing a numerical simulation method according to the actual soaking state of the runner, and the problems that an impulse turbine runner wet mode numerical simulation method is imperfect and low in precision are solved.

Description

Technical Field

[0001] The invention relates to the technical field of impulse turbines, and in particular to a wet mode numerical simulation method for an impulse turbine runner. Background Art

[0002] The runner bucket is the core component of the impulse turbine, responsible for converting the gravitational potential energy of the water body into mechanical energy. During operation, it is subjected to the impact force from the DC nozzle. This impact force has high-frequency alternating characteristics, resulting in the risk of resonance between the runner natural frequency and the excitation frequency. In order to ensure the safe and stable operation of the unit and prevent the runner resonance problem, it is necessary to perform wet modal numerical simulation on the runner of the impulse turbine, extract the runner natural frequency and maintain a certain frequency error margin with the excitation frequency. The existing calculation value of the natural frequency of the impulse runner in water is usually obtained by dry modal numerical simulation, ignoring the influence of the surrounding water on the natural frequency of the runner. This simplified method for solving the natural frequency of the impulse runner in water has low calculation accuracy, resulting in large deviations in the calculated value of the natural frequency of the runner bucket in water, insufficient frequency error margin causing increased resonance risk, and is not conducive to the optimization design of the impulse runner. Summary of the invention

[0003] In order to solve the above technical problems, the present invention proposes a wet mode numerical simulation method for an impulse turbine runner, which can realize the wet mode numerical simulation of the impulse runner according to the actual water distribution state during the operation of the unit by using the fluid-solid coupling analysis method, and solve the problems of imperfect calculation method of the impulse runner's natural frequency in water and low calculation accuracy.

[0004] The present invention is achieved by adopting the following technical solutions:

[0005] A method for numerically simulating wet modes of an impulse turbine runner comprises the following steps:

[0006] S1. Establish a numerical simulation model of the impulse turbine fluid including the water distribution ring pipe, the DC nozzle, and the water body at the runner position, and define the pre-processing settings including the turbulence model, the wall function, and the boundary conditions;

[0007] S2, based on S1, obtain the distribution state of the fluid near the runner bucket of the impulse turbine over time;

[0008] S3. Based on the calculation results of S2, several typical distribution states are selected as the operating points for the wet mode calculation of the impulse runner;

[0009] S4, extracting the fluid unit corresponding to the modal calculation operating point in S3 from the fluid analysis model and transferring it to the wet modal analysis model;

[0010] S5, combining the fluid unit and the impeller structure unit obtained in S4 to establish a complete impingement impeller wet modal analysis model;

[0011] S6. Define the boundary conditions including the freedom constraints of the structural model, the surface constraints of the fluid model, and the fluid-solid coupling between the structure and the fluid;

[0012] S7. Based on S6, the wet modal analysis results of the impact wheel are solved and extracted to obtain the key vibration modes of the wheel and their corresponding natural frequencies.

[0013] In S1, before performing the wet mode calculation of the impulse turbine, the impulse turbine fluid calculation is performed first, a numerical simulation model of the impulse turbine fluid including the water distribution ring pipe, the DC nozzle, and the runner position is established, and pre-processing settings including the turbulence model, the wall function, and the boundary conditions are defined;

[0014] In S2, the impulse turbine fluid analysis model established in S1 is solved to obtain the distribution law of the fluid near the front and back of the runner bucket over time, which refers to the coverage range of the fluid near the bucket, the fluid thickness, and the changes in the coverage range and thickness at different times.

[0015] In S3, based on the calculation result of S2, several typical distribution states are selected as the impact wheel wet mode calculation operating points. The fluid distribution state of each typical calculation operating point is different. Within the range where the DC nozzle passes through two adjacent water buckets, several fluid distribution states can be selected as wet mode calculation operating points at equal time intervals.

[0016] In S4, the fluid units corresponding to the modal calculation operating points in S3 are extracted from the fluid analysis model and transferred to the wet modal analysis model. During the unit transfer process, the fluid units far away from the structural units are reasonably deleted.

[0017] In S5, the fluid unit obtained in S4 is extracted and combined with the impeller structure unit to form a complete impact impeller wet modal analysis model, the structural part model includes the complete impeller bucket and hub, and the fluid part model includes the water body near the impeller bucket surface during operation.

[0018] In S6, reasonable boundary conditions are defined, full constraints are defined at the connection bolt positions between the runner hub and the turbine main shaft, a free surface is defined on the outer surface of the fluid, and a fluid-solid coupling surface is defined at the interface between the structure and the fluid.

[0019] In S7, the wet mode of the impact wheel is solved based on S6, and the wet mode analysis results are extracted, including the key vibration mode of the wheel and its corresponding natural frequency f i, (i=1~10), the key vibration modes refer to the overall torsional vibration mode of the runner, the overall axial vibration mode of the runner, the swing vibration mode of the bucket, and the bending vibration mode of the bucket.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1. The present invention realizes the wet mode numerical simulation of the impulse runner according to the actual water distribution state during the operation of the unit by using the fluid-solid coupling analysis method. This method innovatively fills the gap of the imperfect calculation method of the natural frequency of the impulse runner in water.

[0022] 2. Before performing wet modal calculation of the impulse turbine, the present invention first performs fluid calculation of the impulse turbine to obtain the distribution law of the fluid near the front and back of the impeller bucket changing with time, and establishes a fluid-solid coupling analysis model based on this. The model is closer to the actual working state and can effectively improve the accuracy of numerical simulation.

[0023] 3. The present invention proposes the concept of wet mode numerical simulation operating points. Each operating point has a typical fluid distribution state, which can characterize the wet mode under the action of different water bodies. The influencing factors considered in the analysis are more comprehensive, and the frequency error margin of the impulse turbine runner can be evaluated more accurately to ensure safe and stable operation of the unit. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a flow chart of the numerical simulation method for the wet mode of the impulse turbine runner. DETAILED DESCRIPTION

[0025] The present application is 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 application.

[0026] The numerical simulation method of wet mode of impulse turbine runner is as follows: Figure 1 As shown, the first specific implementation mode includes the following steps:

[0027] S1. Establish a numerical simulation model of the impulse turbine fluid including the water distribution ring pipe, the DC nozzle, and the water body at the runner position, and define the pre-processing settings including the turbulence model, the wall function, and the boundary conditions;

[0028] S2, based on S1, obtain the distribution state of the fluid near the runner bucket of the impulse turbine over time;

[0029] S3. Based on the calculation results of S2, several typical distribution states are selected as the operating points for the wet mode calculation of the impulse runner;

[0030] S4, extracting the fluid unit corresponding to the modal calculation operating point in S3 from the fluid analysis model and transferring it to the wet modal analysis model;

[0031] S5, combining the fluid unit and the impeller structure unit obtained in S4 to establish a complete impingement impeller wet modal analysis model;

[0032] S6. Define the boundary conditions including the freedom constraints of the structural model, the surface constraints of the fluid model, and the fluid-solid coupling between the structure and the fluid;

[0033] S7. Based on S6, the wet modal analysis results of the impact wheel are solved and extracted to obtain the key vibration modes of the wheel and their corresponding natural frequencies.

[0034] In this embodiment, a wet mode numerical simulation method for an impulse turbine runner is proposed. The wet mode numerical simulation of the impulse runner can be realized by utilizing a fluid-solid coupling analysis method according to the actual water distribution state during the operation of the unit, thereby solving the problem of imperfect calculation method of the impulse runner's natural frequency in water and low calculation accuracy.

[0035] Specific implementation method 2: Figure 1 As shown, this embodiment further limits S1 belonging to the specific embodiment one. In this embodiment, in S1, before performing the impulse turbine wet mode calculation, the impulse turbine fluid calculation is first performed, and a numerical simulation model of the impulse turbine fluid including a water distribution ring pipe, a DC nozzle, and a runner position is established, and pre-processing settings including a turbulence model, a wall function, and boundary conditions are defined.

[0036] In this embodiment, a fluid-solid coupling analysis model is established based on the distribution law of the fluid near the front and back of the runner bucket that changes with time. The model is closer to the actual working state and can effectively improve the accuracy of numerical simulation.

[0037] Specific implementation method three: Figure 1 As shown, this embodiment further limits S2 belonging to the specific embodiment one. In this embodiment, in S2, the impulse turbine fluid analysis model established in S1 is solved to obtain the distribution law of the fluid near the front and back of the runner bucket over time. The distribution law refers to the coverage range of the fluid near the bucket, the fluid thickness, and the changes in coverage range and thickness at different times.

[0038] In this implementation, factors considered include the coverage of the fluid near the runner bucket, the fluid thickness and its changes, so as to improve the accuracy of wet mode numerical simulation.

[0039] Specific implementation method four: Figure 1As shown, this embodiment further limits S3 belonging to the specific embodiment one. In this embodiment, in S3, based on the calculation result of S2, several typical distribution states are selected as the impact wheel wet mode calculation operating points. The fluid distribution state of each typical calculation operating point is different. Within the range where the DC nozzle passes through two adjacent water buckets, several fluid distribution states can be selected as wet mode calculation operating points at equal time intervals.

[0040] In this embodiment, the concept of wet mode numerical simulation operating points is proposed. Each operating point has a typical fluid distribution state, which can characterize the wet mode under the action of different water bodies. The influencing factors considered in the analysis are more comprehensive, and the frequency error margin of the impulse turbine runner can be evaluated more accurately to ensure safe and stable operation of the unit.

[0041] Specific implementation method five: Figure 1 As shown, this implementation mode further limits S4 belonging to the specific implementation mode one. In this implementation mode, in S4, the fluid unit corresponding to the modal calculation operating point in S3 is extracted from the fluid analysis model and transferred to the wet modal analysis model. During the unit transfer process, the fluid unit far away from the structural unit is reasonably deleted.

[0042] In this embodiment, the fluid unit is obtained based on the fluid analysis results and is reasonably modified, which can more accurately evaluate the influence of the water body on the natural frequency of the impulse wheel.

[0043] Specific implementation method six: Figure 1 As shown, this embodiment further limits S5 belonging to the specific embodiment one. In this embodiment, in S5, the fluid unit obtained in S4 is extracted and combined with the impeller structure unit to form a complete impact impeller wet modal analysis model. The model of the structural part includes the complete impeller bucket and hub, and the model of the fluid part includes the water body near the surface of the impeller bucket during operation.

[0044] In this embodiment, the fluid unit and the structural unit are combined to form a fluid-solid coupling analysis model, which can truly simulate the influence of the surrounding water body on the natural frequency of the impact wheel.

[0045] Specific implementation method seven: Figure 1 As shown, this embodiment further limits S6 belonging to the specific embodiment 1. In this embodiment, in S6, reasonable boundary conditions are defined, full constraints are defined at the connection bolt positions between the runner hub and the turbine main shaft, a free surface is defined on the outer surface of the fluid, and a fluid-solid coupling surface is defined at the interface between the structure and the fluid.

[0046] In this implementation, the fluid-solid coupling solver pre-processing settings are defined by combining engineering practice with various aspects of numerical simulation experience, providing basic conditions for carrying out numerical simulation of wet modes of impact impellers.

[0047] Specific implementation method eight: Figure 1 As shown, this embodiment further limits S7 of the specific embodiment 1. In this embodiment, in S7, the wet mode of the impact wheel is solved based on S6, and the wet mode analysis results are extracted. The results include the key vibration mode of the wheel and its corresponding natural frequency f i , (i=1~10), the key vibration modes refer to the overall torsional vibration mode of the runner, the overall axial vibration mode of the runner, the swing vibration mode of the bucket, and the bending vibration mode of the bucket.

[0048] In this implementation, the key vibration modes that need to be paid attention to in the impact wheel are determined, and the natural frequencies and exciting frequencies corresponding to the key vibration modes are obtained by comparing the wet modes, thus laying a foundation for the vibration avoidance design of the impact wheel.

[0049] The above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Although the present invention has been described in detail with reference to the above embodiments, it should be clear to those skilled in the art that the technical solutions described in the above embodiments may be modified, or some or all of the technical features therein may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for numerically simulating wet modes of an impulse turbine runner, comprising the following steps: S1. Establish a numerical simulation model of the impulse turbine fluid including the water distribution ring pipe, the DC nozzle, and the water body at the runner position, and define the pre-processing settings including the turbulence model, the wall function, and the boundary conditions; S2, based on S1, obtain the distribution state of the fluid near the runner bucket of the impulse turbine over time; S3. Based on the calculation results of S2, several typical distribution states are selected as the operating points for the wet mode calculation of the impulse runner; S4, extracting the fluid unit corresponding to the modal calculation operating point in S3 from the fluid analysis model and transferring it to the wet modal analysis model; S5, combining the fluid unit and the impeller structure unit obtained in S4 to establish a complete impingement impeller wet modal analysis model; S6. Define the boundary conditions including the freedom constraints of the structural model, the surface constraints of the fluid model, and the fluid-solid coupling between the structure and the fluid; S7. Based on S6, the wet modal analysis results of the impact wheel are solved and extracted to obtain the key vibration modes of the wheel and their corresponding natural frequencies.

2. The method for numerical simulation of wet modes of an impulse turbine runner according to claim 1, characterized in that: In S1, before performing the wet mode calculation of the impulse turbine, the impulse turbine fluid calculation is performed first, a numerical simulation model of the impulse turbine fluid including the water distribution ring pipe, the DC nozzle, and the impeller position is established, and pre-processing settings including the turbulence model, the wall function, and the boundary conditions are defined.

3. The method for numerical simulation of wet modes of an impulse turbine runner according to claim 2, characterized in that: In S2, the impulse turbine fluid analysis model established in S1 is solved to obtain the distribution law of the fluid near the front and back of the runner bucket over time, which refers to the coverage range of the fluid near the bucket, the fluid thickness, and the changes in the coverage range and thickness at different times.

4. The method for numerical simulation of wet modes of an impulse turbine runner according to claim 3, characterized in that: In S3, based on the calculation results of S2, several typical distribution states are selected as the impact wheel wet mode calculation operating points, and the fluid distribution state of each typical calculation operating point is different. Within the range where the DC nozzle passes through two adjacent water buckets, several fluid distribution states are selected as wet mode calculation operating points at equal time intervals.

5. The method for numerical simulation of wet modes of an impulse turbine runner according to claim 4, characterized in that: In S4, the fluid units corresponding to the modal calculation operating points in S3 are extracted from the fluid analysis model and transferred to the wet modal analysis model. During the unit transfer process, the fluid units far away from the structural units are reasonably deleted.

6. The method for numerical simulation of wet modes of an impulse turbine runner according to claim 5, characterized in that: In S5, the fluid unit obtained in S4 is extracted and combined with the impeller structure unit to form a complete impact impeller wet modal analysis model, the structural part model includes the complete impeller bucket and hub, and the fluid part model includes the water body near the impeller bucket surface during operation.

7. The method for numerical simulation of wet modes of an impulse turbine runner according to claim 6, characterized in that: In S6, reasonable boundary conditions are defined, full constraints are defined at the connection bolt positions between the runner hub and the turbine main shaft, a free surface is defined on the outer surface of the fluid, and a fluid-solid coupling surface is defined at the interface between the structure and the fluid.

8. The method for numerical simulation of wet modes of an impulse turbine runner according to claim 7, characterized in that: In S7, the wet mode of the impact wheel is solved based on S6, and the wet mode analysis results are extracted, including the key vibration mode of the wheel and its corresponding natural frequency f i , (i=1~10), the key vibration modes refer to the overall torsional vibration mode of the runner, the overall axial vibration mode of the runner, the water bucket swing vibration mode, and the water bucket bending vibration mode.

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