Finite element calculation method for blade adopting shroud ring shroud ring structure

Abstract

The invention relates to a finite element calculation method, in particular to a finite element calculation method for a blade adopting a shroud ring shroud ring structure. The method aims at solving the problem that in the prior art, safety checking cannot be conducted on a blade with a shroud ring and shroud ring structure through a finite element method. According to the method, safety checking of the hoop shroud ring structure can be carried out, finite element calculation software is adopted for three-dimensional simulation and analysis calculation, the safety of the hoop shroud ring structure is checked through a finite element calculation method, and especially the strength and vibration characteristics of the hoop shroud ring structure and the stress level of a shroud ring connecting strip can be investigated; and the frequency value of the blade can be intuitively obtained, which is very important for the safety design and examination of the shroud ring shroud ring blade and ensures that the turbine blade can operate safely and reliably. The invention belongs to the technical field of turbine blades.

Description

Technical Field

[0001] The invention relates to a finite element calculation method, in particular to a finite element calculation method for a blade adopting a hoop-wrapped belt structure, and belongs to the technical field of steam turbine blades. Background Art

[0002] Many medium-long blades (about 200-300mm in height) in steam turbine factories are not suitable for designing as pre-twisted blades or frequency-modulated blades. For the vibration safety of the blades, adding shroud connecting strips to form a hoop-shroud structure with independent shrouds at the top of each blade becomes a good measure. In order to ensure safe operation, it is very important to perform finite element calculations on this structure in the design work.

[0003] In summary, how to propose a finite element calculation method to address the above technical issues has become an urgent problem to be solved by technicians in this field. Summary of the invention

[0004] In view of the above-mentioned deficiencies in the prior art, the present invention provides a finite element calculation method for a blade adopting a hoop shroud structure.

[0005] The technical solution of the present invention is: a finite element calculation method for a blade using a hoop-wrapped band structure, which is specifically performed in the following steps:

[0006] Step 1: Create a solid model for calculation

[0007] Step 1: Solid Modeling

[0008] Establishing a model of a rotor, a blade, a first shroud connecting strip, and a second shroud connecting strip in a modeling software;

[0009] The blade top is integrally provided with a shroud, and a dovetail groove is provided on the outer circumference of the shroud;

[0010] The cross sections of the first shroud connecting strip and the second shroud connecting strip are both right-angled trapezoidal, and the first shroud connecting strip and the second shroud connecting strip are both assembled in the dovetail groove;

[0011] The butt joint of the first shroud connecting strip and the butt joint of the second shroud connecting strip are both arranged in the dovetail groove, and the two butt joints are staggered in the circumferential direction;

[0012] Step 12: setting the model constructed in step 11 to be cyclically symmetrical, wherein the model after the cyclically symmetrical setting includes a rotor with one pitch, a first shroud connecting strip, and a second shroud connecting strip;

[0013] Step 13: Save the model in step 1 and 2 as a solid model in stp format;

[0014] Step 2: Import the solid model in step 1 and 3 into ANSA software to draw the mesh and obtain the mesh model in inp format;

[0015] Step 3: Import the mesh model in step 2 into the finite element calculation software to set parameters;

[0016] Step 31: Assign material properties to the mesh model;

[0017] Step 32: Define boundary conditions for the grid model. The boundary conditions include at least:

[0018] Define the contact friction coefficient between the rotor and the blades;

[0019] defining a contact friction coefficient between the first shroud connecting strip and the shroud;

[0020] defining the contact friction coefficient between the second shroud connecting strip and the shroud;

[0021] defining a contact friction coefficient between the first shroud connecting strip and the second shroud connecting strip;

[0022] Define the contact pairs between the rotor and the blades;

[0023] Define the contact pair and contact gap between the first shroud connection strip and the shroud, and assign contact control and tolerance to the contact pair;

[0024] Define the contact pair and contact gap between the second shroud connection strip and the shroud, and assign contact control and tolerance to the contact pair;

[0025] defining a contact pair between the first shroud connecting strip and the second shroud connecting strip;

[0026] Define radial constraints on the rotor's center of rotation;

[0027] Define the axial and circumferential constraints on the rotor end surface;

[0028] Define a cyclic symmetry surface and impose cyclic symmetry constraints on the cyclic symmetry surface;

[0029] Step 3: Define the operating conditions for the grid model. The operating conditions include at least:

[0030] Steam forces exerted on the blade profile surface of the blade;

[0031] Apply the operating temperature and centrifugal force of the entire grid model;

[0032] Define the stress analysis step, temperature analysis step and vibration frequency analysis step of the entire mesh model;

[0033] Step 4: Use finite element calculation software to perform calculations.

[0034] Compared with the prior art, the present invention has the following effects:

[0035] 1. The present invention can perform safety verification of the hoop belt structure, adopt finite element calculation software to perform three-dimensional simulation and analytical calculation, and use finite element calculation method to verify the safety of the hoop belt structure, especially it can examine the strength and vibration characteristics of the hoop belt structure, the stress level at the belt connecting strip, and can intuitively obtain the blade frequency value, which is very important for the safety design and assessment of the hoop belt blade, ensuring that the turbine blade can operate safely and reliably. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 is an axonometric view of the rotor 1 and blade 2 of the present invention;

[0037] Figure 2 It is a schematic diagram of the first shroud connecting strip 201 and the second shroud connecting strip 202 of the present invention being assembled in the shroud;

[0038] Figure 3 It is an axonometric view of the first shroud connecting strip 201 and the second shroud connecting strip 202 of the present invention.

[0039] In the figure: 1, rotor; 2, blade; 201, first shroud connecting strip; 202, second shroud connecting strip. DETAILED DESCRIPTION

[0040] In order to make the purpose, features and advantages of the present invention more obvious and understandable, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0041] Specific implementation method 1: Combination Figures 1 to 3 To illustrate this embodiment, a finite element calculation method for a blade using a hoop-wrapped band structure is specifically performed in the following steps:

[0042] Step 1: Create a solid model for calculation

[0043] Step 1: Solid Modeling

[0044] A model of the rotor 1 , a blade 2 , a first shroud connecting strip 201 , and a second shroud connecting strip 202 is established in the modeling software.

[0045] The blade top of the blade 2 is integrally provided with a shroud, and a dovetail groove is provided on the outer circumferential surface of the shroud.

[0046] The cross sections of the first shroud connecting strip 201 and the second shroud connecting strip 202 are both right-angled trapezoids, and the first shroud connecting strip 201 and the second shroud connecting strip 202 are both assembled in the dovetail groove.

[0047] The butt joint of the first shroud connecting strip 201 and the butt joint of the second shroud connecting strip 202 are both arranged in the dovetail groove, and the two butt joints are staggered in the circumferential direction.

[0048] Step 12: Perform cyclic symmetry on the model constructed in step 11. The model after cyclic symmetry includes a rotor 1 with one pitch, a first shroud connecting strip 201 and a second shroud connecting strip 202.

[0049] Furthermore, the mechanism for adopting the cyclic symmetric setting is:

[0050] If an object, including its material constants, remains exactly the same as before rotation every time it rotates around its axis of rotation by an angle α, the structure of the object is called a cyclically symmetric structure.

[0051] In practice, N identical blades 2 are installed on the rotor 1, and the geometric shape, material properties and boundary conditions of the blades 2 are the same. In this case, the blade-rotor system is an N-order cyclically symmetrical structure, and the axis of rotation of the rotor 1 is the cyclic symmetry axis. According to the characteristics of this structure, as long as one of the cyclically symmetrical structures is analyzed and calculated, the solution of the entire blade-rotor system can be obtained, thereby greatly simplifying the analysis and solution of the entire blade-rotor system.

[0052] Step 13: Save the model in step 1 and 2 as a solid model in stp format.

[0053] Step 2: Import the solid model in steps 1 and 3 into ANSA software to draw the mesh and obtain the mesh model in inp format.

[0054] Step 3: Import the mesh model in step 2 into the finite element calculation software for parameter setting.

[0055] Step 31: Assign material properties to the mesh model.

[0056] Step 32: Define boundary conditions for the grid model. The boundary conditions include at least:

[0057] Define the contact friction coefficient between rotor 1 and blade 2.

[0058] The contact friction coefficient between the first shroud connecting strip 201 and the shroud is defined.

[0059] The contact friction coefficient between the second shroud connecting strip 202 and the shroud is defined.

[0060] The contact friction coefficient between the first shroud connecting strip 201 and the second shroud connecting strip 202 is defined.

[0061] A contact pair between the rotor 1 and the blade 2 is defined. In this way, the dynamic contact between the rotor 1 and the blade 2 is simulated through the contact pair.

[0062] The contact pairs and contact gaps between the first shroud connecting strip 201 and the shroud are defined. Since the cross-section of the first shroud connecting strip 201 is a right-angled trapezoid, contact pairs are provided between the lower bottom surface and the inclined surface of the first shroud connecting strip 201 and the shroud, and contact control and tolerance are given to the contact pairs.

[0063] Contact gap: refers to the initial separation distance between two surfaces. If the contact gap between two surfaces is 0, the two surfaces are considered to be in contact, and the force can be transmitted between the contacting surfaces and the magnitude is not limited.

[0064] Contact control: the management and control of the interaction between contact surfaces, including the selection of contact algorithms, the definition of contact pairs, the specification of contact properties, and the adjustment of contact behavior. It can finely manage contact behavior and improve the accuracy and stability of finite element calculations.

[0065] Tolerance: Since deviations are inevitable in the actual manufacturing or assembly process of parts, an error limit should generally be set for the deviation between the contact surfaces of two or more parts when defining contact. The error limit here refers to the tolerance.

[0066] The contact pairs and contact gaps between the second shroud connecting strip 202 and the shroud are defined. Since the cross-section of the second shroud connecting strip 202 is a right-angled trapezoid, contact pairs are provided between the lower bottom surface and the inclined surface of the second shroud connecting strip 202 and the shroud, and contact control and tolerance are given to the contact pairs.

[0067] A contact pair is defined between the first shroud connecting strip 201 and the second shroud connecting strip 202. Further, since the cross-sections of the first shroud connecting strip 201 and the second shroud connecting strip 202 are right-angled trapezoids, a contact pair is provided between the side elevations of the first shroud connecting strip 201 and the second shroud connecting strip 202.

[0068] Further, the butt joint of the first shroud connecting strip 201 is provided with a contact pair;

[0069] Furthermore, the joint of the second shroud connecting strip 202 is provided with a contact pair.

[0070] Define the radial constraint of the rotation center of rotor 1;

[0071] Define the axial constraint and circumferential constraint of the end face of rotor 1;

[0072] Define the cyclic symmetry surface and ensure that it is not over-constrained, and impose cyclic symmetry constraints on it.

[0073] Step 3: Define the operating conditions for the grid model. The operating conditions include at least:

[0074] Steam force applied to the blade surface of blade 2;

[0075] Apply the operating temperature and centrifugal force of the entire grid model;

[0076] Define the stress analysis step, temperature analysis step and vibration frequency analysis step of the entire mesh model. Furthermore, the analysis step refers to dividing the entire loading and solution process into several sub-stages, and each sub-stage is called an analysis step.

[0077] Step 4: Use finite element calculation software to perform calculations.

[0078] Specific implementation method 2: Combination Figures 1 to 3 To illustrate this implementation, in step 1 of this implementation, UG-NX software is selected for modeling.

[0079] Furthermore, in step 2, the first shroud connecting strip 201 and the second shroud connecting strip 202 both use hexahedral meshes, and the hexahedral meshes are both mesh aligned, so that the mesh nodes are aligned, which can ensure that the arrangement of the meshes remains consistent, thereby improving the quality of the meshes and the accuracy of the calculation.

[0080] The rotor 1 adopts a pentahedral grid or a hexahedral grid. Preferably, a pentahedral grid is selected at the circumferential center of the rotor 1, and the rest of the rotor 1 adopts a hexahedral grid.

[0081] The blade root and blade transition area of ​​the blade 2 use tetrahedral or pentahedral meshes, and the rest of the blade 2 uses hexahedral meshes.

[0082] Furthermore, in step three, ABAQUS software is used for parameter setting.

[0083] Furthermore, in step 3-1, the material properties include at least density, elastic modulus, specific heat capacity and linear expansion coefficient.

[0084] Furthermore, in step 4, ABAQUS software is used for calculation.

[0085] Other components and connection relationships are the same as those in the first specific implementation method.

[0086] The present invention has been disclosed as above in the form of a preferred embodiment, but it is not intended to limit the present invention. Any simple modification, equivalent changes and modifications made to the above implementation cases by any professional and technical personnel who do not deviate from the content of the technical solution of the present invention and based on the technical essence of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A finite element calculation method for a blade using a hoop-band structure, characterized in that: The method is specifically carried out in the following steps: Step 1: Create a solid model for calculation Step 1: Solid Modeling Establishing a model of a rotor (1), a blade (2), a first shroud connecting strip (201) and a second shroud connecting strip (202) in a modeling software; The blade top of the blade (2) is integrally provided with a shroud, and a dovetail groove is provided on the outer circumferential surface of the shroud; The cross-sections of the first shroud connecting strip (201) and the second shroud connecting strip (202) are both right-angled trapezoids, and the first shroud connecting strip (201) and the second shroud connecting strip (202) are both assembled in the dovetail groove; The butt joint of the first shroud connecting strip (201) and the butt joint of the second shroud connecting strip (202) are both arranged in the dovetail groove, and the two butt joints are staggered in the circumferential direction; Step 12: setting the model constructed in step 11 to be cyclically symmetrical, wherein the model after the cyclically symmetrical setting includes a rotor (1) with a pitch, a first shroud connecting strip (201) and a second shroud connecting strip (202); Step 13: Save the model in step 1 and 2 as a solid model in stp format; Step 2: Import the solid model in step 1 and 3 into ANSA software to draw the mesh and obtain the mesh model in inp format; Step 3: Import the mesh model in step 2 into the finite element calculation software to set parameters; Step 31: Assign material properties to the mesh model; Step 32: Define boundary conditions for the grid model. The boundary conditions include at least: defining a contact friction coefficient between the rotor (1) and the blade (2); defining a contact friction coefficient between the first shroud connecting strip (201) and the shroud; defining a contact friction coefficient between the second shroud connecting strip (202) and the shroud; defining a contact friction coefficient between the first shroud connecting strip (201) and the second shroud connecting strip (202); defining a contact pair between a rotor (1) and a blade (2); defining a contact pair and a contact gap between the first shroud connection strip (201) and the shroud, and assigning contact control and tolerance to the contact pair; defining a contact pair and a contact gap between the second shroud connection strip (202) and the shroud, and assigning contact control and tolerance to the contact pair; defining a contact pair between the first shroud connecting strip (201) and the second shroud connecting strip (202); defining a radial constraint on the center of rotation of the rotor (1); defining axial constraints and circumferential constraints on the end surface of the rotor (1); Define a cyclic symmetry surface and impose cyclic symmetry constraints on the cyclic symmetry surface; Step 3: Define the operating conditions for the grid model. The operating conditions include at least: Steam force exerted on the blade surface of the blade (2); Apply the operating temperature and centrifugal force of the entire grid model; Define the stress analysis step, temperature analysis step and vibration frequency analysis step of the entire mesh model; Step 4: Use finite element calculation software to perform calculations.

2. The finite element calculation method for a blade using a hoop-shaped shroud structure according to claim 1, characterized in that: In the step 1, UG-NX software is used for modeling.

3. The finite element calculation method for a blade using a hoop-shaped shroud structure according to claim 2, characterized in that: In the step 2, both the first shroud connecting strip (201) and the second shroud connecting strip (202) are formed using hexahedral grids; The rotor (1) adopts a pentahedral grid or a hexahedral grid; The blade root and blade transition area of ​​the blade (2) use tetrahedral or pentahedral grids, and the remaining parts of the blade (2) use hexahedral grids.

4. The finite element calculation method for a blade using a hoop-shaped shroud structure according to claim 3, characterized in that: In the step three, ABAQUS software is used to set parameters.

5. The finite element calculation method for a blade using a hoop-shaped shroud structure according to claim 4, characterized in that: The material properties in step 31 at least include density, elastic modulus, specific heat capacity and linear expansion coefficient.

6. The finite element calculation method for a blade using a hoop-shaped shroud structure according to claim 5, characterized in that: In the step 4, ABAQUS software is used for calculation.

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