Frequency modulation method for long blades of steam turbine

Abstract

The application provides a frequency adjustment method for a long blade of a steam turbine, comprising the following steps: each steam turbine long blade model is designed with different elliptical fillets at the connection of the blade profile and the shroud, the lengths of the major axes of all the elliptical fillets are different, and the lengths of the minor axes of all the elliptical fillets are equal; finite element analysis is respectively performed on all the steam turbine long blade models to calculate multiple natural frequencies with different orders for each steam turbine long blade model; the long blade part is manufactured according to the elliptical fillet with the maximum length of the major axis first, and then dynamic frequency test is performed on the long blade part; if the result of the dynamic frequency test does not meet the design requirement, the elliptical fillet is ground based on the change rule to gradually reduce the length of the major axis, and then the dynamic frequency test is performed again, and the operation is repeated until the result of the dynamic frequency test of the long blade part meets the design requirement. The application can effectively adjust the frequency of the long blade part.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of steam turbine, in particular to a frequency adjustment method of long blade of steam turbine. BACKGROUND

[0002] In the design of the whole-circle self-locking damping long blade of steam turbine, the common frequency adjustment method is through the different thickness of the shroud or the different height of the stay. In the design of the long blade below the full speed 1 meter level, the above two frequency adjustment methods are effective. However, in the design of the long blade above the 1 meter level, the thickness of the shroud is small relative to the height of the long blade itself, the different thickness has a little influence on the first order natural frequency of the blade, and has little influence on the second order and above natural frequencies, and the change of the shroud thickness brings a small change value of the natural frequency of the blade.

[0003] The change of the height of the stay has a certain frequency adjustment effect on the second order natural frequency of the blade, and has little influence on the first order frequency. In addition, the change of the height of the stay also has a great influence on the static stress distribution of the blade itself. SUMMARY

[0004] In view of the above-mentioned defects of the prior art, the technical problem to be solved by the present application is to provide a frequency adjustment method of long blade of steam turbine, which can play a very effective frequency adjustment effect on the long blade part.

[0005] In order to solve the above technical problems, the present application provides a frequency adjustment method of long blade of steam turbine, the long blade of steam turbine comprising a blade profile and a shroud, the shroud being formed at one end of the blade profile in the height direction, the frequency adjustment method comprising the following steps:

[0006] A plurality of long blade models of steam turbine are established by using modeling software, each long blade model of steam turbine is designed with different elliptical fillets at the connection of the blade profile and the shroud, the lengths of the major axes of all the elliptical fillets are different from each other, and the lengths of the minor axes of all the elliptical fillets are equal;

[0007] The finite element analysis is respectively performed on all the long blade models of steam turbine, the multiple natural frequencies of different orders of each long blade model of steam turbine are calculated, and the change law between the major axis of the elliptical fillet and the natural frequency of the long blade model of steam turbine is obtained;

[0008] Firstly, the long blade part is manufactured according to the elliptical fillet with the maximum length of the major axis, then the dynamic frequency test is performed on the long blade part, if the result of the dynamic frequency test meets the design requirements, the frequency adjustment is ended, if the result of the dynamic frequency test does not meet the design requirements, the elliptical fillet is ground based on the change law so that the length of the major axis gradually decreases, and the dynamic frequency test is performed again, and the above operations are repeated until the result of the dynamic frequency test of the long blade part meets the design requirements.

[0009] Preferably, the height of the airfoil is not less than one meter.

[0010] Preferably, the number of the steam turbine long blade models is not less than three.

[0011] Preferably, the length of the long axis of all the elliptical fillets ranges from 10 to 50 mm.

[0012] Preferably, the calculation condition of the natural frequency is that the steam turbine long blade model is in a motion state at a rated rotating speed.

[0013] Preferably, the natural frequency of the steam turbine long blade model includes a first-order natural frequency, a second-order natural frequency and a third-order natural frequency.

[0014] As described above, the frequency tuning method of the steam turbine long blade has the following beneficial effects: the different elliptical fillets at the connection between the airfoil and the shroud are designed, which is equivalent to increasing the thickness of the top of the airfoil, and further increasing the overall stiffness of the steam turbine long blade, so as to increase the natural frequency of the steam turbine long blade to different degrees, thereby playing a frequency tuning role on the steam turbine long blade. Based on this, the frequency tuning method changes the natural frequency of the steam turbine long blade by modifying the length of the long axis of the elliptical fillet at the connection between the airfoil and the shroud. Specifically, a modeling software is used to establish a plurality of steam turbine long blade models, each of which is designed with a different elliptical fillet at the connection between the airfoil and the shroud, the lengths of the long axes of all the elliptical fillets are different from each other, and the lengths of the short axes of all the elliptical fillets are equal; finite element analysis is respectively performed on all the steam turbine long blade models to calculate a plurality of natural frequencies with different orders for each steam turbine long blade model, and a change rule between the length of the long axis of the elliptical fillet and the natural frequency of the steam turbine long blade model is obtained; the long blade part is first manufactured according to the elliptical fillet with the longest long axis, then a dynamic frequency test is performed on the long blade part, if the result of the dynamic frequency test meets the design requirements, the frequency tuning ends, if the result of the dynamic frequency test does not meet the design requirements, the elliptical fillet is ground based on the change rule to gradually reduce the length of the long axis, and then the dynamic frequency test is performed, and the above operations are repeated until the result of the dynamic frequency test of the long blade part meets the design requirements. Therefore, the above frequency tuning method can effectively tune the long blade part. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 shows a cross-sectional view of the steam turbine long blade of the present application;

[0016] Figure 2 shows a schematic view of an elliptical fillet with a long axis of 40 mm;

[0017] Figure 3A schematic view of an elliptical rounding shown as having a major axis of 30 mm;

[0018] Figure 4 A schematic view of an elliptical rounding shown as having a major axis of 20 mm.

[0019] Element number explanation

[0020] 1 blade profile

[0021] 2 shroud

[0022] 3 elliptical rounding DETAILED DESCRIPTION

[0023] The embodiments of the present application will be described in detail by the following specific examples, and other advantages and effects of the present application can be easily understood by those skilled in the art from the contents disclosed in the specification.

[0024] It should be noted that the structures, proportions, sizes, etc. shown in the drawings attached to the specification are only used to cooperate with the contents disclosed in the specification for understanding and reading by those skilled in the art, and do not define the limiting conditions for implementing the present application, and therefore do not have technical substantive significance. Any modification of the structure, change of the proportional relationship, or adjustment of the size, without affecting the effects and purposes that can be achieved by the present application, should still fall within the scope of the technical content disclosed by the present application. At the same time, the terms such as "upper", "lower", "left", "right", "middle", and "one" used in the specification are only for the convenience of clear description, and are not used to limit the scope of the present application. The change or adjustment of the relative relationship, without substantially changing the technical content, is also considered as the scope of the present application.

[0025] As shown in Figure 1 , Figure 2 , Figure 3 and Figure 4 , the long blade of the steam turbine includes a blade profile 1 and a shroud 2 formed at one end of the blade profile 1 in the height direction.

[0026] Therefore, the present application provides a frequency modulation method for a long blade of a steam turbine, which includes the following steps:

[0027] A plurality of long blade models of the steam turbine are established using modeling software, each long blade model of the steam turbine is designed with different elliptical roundings 3 at the connection between the blade profile 1 and the shroud 2, the lengths of the major axes of all the elliptical roundings 3 are different from each other, and the lengths of the minor axes of all the elliptical roundings 3 are equal;

[0028] Carry out finite element analysis on all the steam turbine long blade models respectively, calculate multiple natural frequencies of different orders of each steam turbine long blade model, and obtain the variation law between the long axis of the elliptical round 3 and the natural frequency of the steam turbine long blade model;

[0029] First, the long blade part is manufactured according to the elliptical round 3 with the longest long axis, then the dynamic frequency test is carried out on the long blade part, if the result of the dynamic frequency test meets the design requirement, the frequency adjustment is ended, if the result of the dynamic frequency test does not meet the design requirement, the elliptical round 3 is ground based on the above variation law to gradually reduce the length of the long axis, and then the dynamic frequency test is carried out, and the operation is repeated until the result of the dynamic frequency test of the long blade part meets the design requirement.

[0030] In the present application, when the height of the blade profile 1 of the steam turbine long blade is above 1 meter, the top of the blade profile 1 is relatively thin relative to the overall height of the steam turbine long blade, and the rigidity is small. Different elliptical rounds 3 are used to design the connection between the blade profile 1 and the shroud 2, which is equivalent to increasing the thickness of the top of the blade profile 1, and further increasing the overall rigidity of the steam turbine long blade, thereby increasing the natural frequency (usually the first-order natural frequency, the second-order natural frequency and the third-order natural frequency) of the steam turbine long blade to different degrees, and playing a frequency adjustment role on the steam turbine long blade. Based on this, the frequency adjustment method of the present application changes the natural frequency of the steam turbine long blade by modifying the size of the long axis of the elliptical round 3 at the connection between the blade profile 1 and the shroud 2. Specifically, a modeling software is used to establish multiple steam turbine long blade models, each steam turbine long blade model is designed with different elliptical rounds 3 at the connection between the blade profile 1 and the shroud 2, the lengths of the long axes of all the elliptical rounds 3 are different, and the lengths of the short axes of all the elliptical rounds 3 are equal; finite element analysis is carried out on all the steam turbine long blade models respectively, multiple natural frequencies of different orders of each steam turbine long blade model are calculated, and the variation law between the long axis of the elliptical round 3 and the natural frequency of the steam turbine long blade model is obtained; first, the long blade part is manufactured according to the elliptical round 3 with the longest long axis, then the dynamic frequency test is carried out on the long blade part, if the result of the dynamic frequency test meets the design requirement, the frequency adjustment is ended, if the result of the dynamic frequency test does not meet the design requirement, the elliptical round 3 is ground based on the above variation law to gradually reduce the length of the long axis, and then the dynamic frequency test is carried out, and the operation is repeated until the result of the dynamic frequency test of the long blade part meets the design requirement. Therefore, the above frequency adjustment method can effectively adjust the frequency of the long blade part.

[0031] Because the above frequency adjustment method has a more effective frequency adjustment effect on longer steam turbine long blades, the height of the blade profile 1 is not less than 1 meter.

[0032] Generally, the number of the above turbine long blade models is not less than three. For example, if the length of the long axis of the elliptical round 3 is denoted as A, and the length of the short axis of the elliptical round 3 is denoted as B, the long axes of the three elliptical rounds 3 corresponding to the three turbine long blade models are respectively denoted as A1, A2 and A3, and the condition of A1>A2>A3 is satisfied. Further, the length of the long axis of the three above elliptical rounds 3 ranges from 10mm to 50mm, for example, the length of the long axis is respectively 40mm, 30mm and 20mm.

[0033] The calculation condition of the above natural frequency is that the turbine long blade model is in a motion state at a rated speed, for example, in a motion state at 3000r / min.

[0034] The natural frequency of the above turbine long blade model includes a first-order natural frequency, a second-order natural frequency and a third-order natural frequency.

[0035] Taking a turbine long blade of one-meter level or above as an example:

[0036] If the existing frequency modulation method is adopted, the thickness of the shroud 2 is reduced from 18mm to 12mm, the reduction rate of the first-order natural frequency of the turbine long blade is 0.02Hz / mm (i.e. 0.02Hz is reduced per 1mm), the reduction rate of the second-order natural frequency is 0.08Hz / mm, and the increase rate of the third-order natural frequency is 0.03Hz / mm; if the position of the reinforcing rib (the reinforcing rib is formed on the blade profile 2) is raised from 55% of the height of the blade profile 2 to 60% of the height of the blade profile 2, the increase rate of the first-order natural frequency of the turbine long blade is 1Hz / mm, the increase rate of the second-order natural frequency is 4Hz / mm, and the increase rate of the third-order natural frequency is 2Hz / mm.

[0037] Using the frequency modulation method of the present application, the same three turbine long blade models are established by using modeling software, and each turbine long blade model is designed with an elliptical round 3 at the connection between the blade profile 1 and the shroud 2, the length of the long axis A of the three elliptical rounds 3 is respectively taken as 40mm (see Figure 2 ), 30mm (see Figure 3 ) and 20mm (see Figure 4 ). Through finite element analysis, the first-order natural frequency, the second-order natural frequency and the third-order natural frequency of the turbine long blade model under the condition of 3000r / min are obtained, and the specific results are shown in Table 1. From Table 1, it can be seen that when the length A of the long axis of the elliptical round 3 is increased from 20mm to 40mm, the first-order natural frequency of the turbine long blade model is increased by about 2Hz, the second-order natural frequency is increased by about 3Hz, and the third-order natural frequency is increased by about 4Hz per 10mm increase of the length A of the long axis of the elliptical round 3, and the frequency modulation effect is very good.

[0038] Table 1 Natural frequency values of the long blade of the steam turbine corresponding to the long axis of the elliptical round

[0039]

[0040] In summary, the present application can play a very effective frequency modulation effect on the long blade parts. Therefore, the present application effectively overcomes the various shortcomings in the prior art and has a high industrial utilization value.

[0041] The above embodiments only illustrate the principles and effects of the present application, and are not intended to limit the present application. Any person skilled in the art can modify or change the above embodiments without departing from the spirit and scope of the present application. Therefore, all equivalent modifications or changes made by those skilled in the art without departing from the spirit and technical ideas disclosed by the present application should be covered by the claims of the present application.

Claims

1. A method for frequency modulation of a long turbine blade, wherein the long turbine blade comprises a blade profile (1) and a shroud (2), the shroud (2) being formed at one end of the blade profile (1) in the height direction, characterized in that, The frequency modulation method includes the following steps: Multiple identical steam turbine long blade models are created using modeling software. Each steam turbine long blade model is designed with different elliptical rounding (3) at the connection between the blade (1) and the shroud (2). The lengths of the major axes of all elliptical rounding (3) are not equal, while the lengths of the minor axes of all elliptical rounding (3) are equal. Finite element analysis was performed on all the turbine long blade models respectively, and multiple natural frequencies of different orders for each turbine long blade model were calculated. The variation law between the major axis of the elliptical rounded (3) and the natural frequency of the turbine long blade model was obtained. First, the long blade part is manufactured by making an elliptical rounded shape (3) with the major axis as the maximum length. Then, the long blade part is subjected to a dynamic frequency test. If the result of the dynamic frequency test meets the design requirements, the frequency tuning ends. If the result of the dynamic frequency test does not meet the design requirements, the elliptical rounded shape (3) is ground according to the change law to make the length of the major axis gradually smaller. Then, the dynamic frequency test is performed again. This operation is repeated until the result of the dynamic frequency test of the long blade part meets the design requirements.

2. The frequency modulation method for long turbine blades according to claim 1, characterized in that: The height of the blade (1) is not less than one meter.

3. The frequency modulation method for long turbine blades according to claim 1, characterized in that: The number of turbine long blade models shall not be less than three.

4. The frequency modulation method for long turbine blades according to claim 3, characterized in that: The length of the major axis of all the described elliptical rounded (3) ranges from 10 to 50 mm.

5. The frequency modulation method for long turbine blades according to claim 1, characterized in that: The natural frequency is calculated under the condition that the turbine long blade model is in motion at its rated speed.

6. The frequency modulation method for long turbine blades according to claim 1, characterized in that: The natural frequencies of the turbine long blade model include the first-order natural frequency, the second-order natural frequency, and the third-order natural frequency.

Images