Cold-state blade tip gap design method

Abstract

The invention provides a cold-state blade tip gap design method which comprises the following steps: S1, establishing a blade thermal-state design model and a flow field grid, and enabling the blade thermal-state design model to have an equal blade tip gap structure; s2, converting the blade thermal state design model into a cold state blade initial model; s3, calculating the thermal-state radial deformation of the blade tip by using a computational fluid mechanics method; and S4, subtracting the blade tip thermal-state radial deformation from the blade tip height of the blade thermal-state design model to obtain a cold-state blade correction model. According to the method, the local height and the surface shape of the blade tip of the turbine movable blade in the cold state are obtained through reverse deduction by calculating the local deformation of the blade in the main working state of the turbine movable blade, and therefore it is guaranteed that the blade tip gap is uniform in the working state of the movable blade.

Description

Technical Field

[0001] The present invention relates to the field of blade design, and in particular to the field of blade tip clearance. Background Art

[0002] The turbine blades of aircraft engines and gas turbines need to work in a high temperature and high pressure environment for a long time, especially the working blades, that is, the moving blades need to rotate at high speed. In such a working environment, the turbine moving blades are subjected to multiple effects of aerodynamic force, thermal load and centrifugal force, which causes local deformation and stress in the blades. While this part of the force affects the life of the blades, the local deformation of the blades in the circumferential and radial directions also affects their aerodynamic performance, especially in the radial direction, which directly affects the local change of the tip clearance, making the tip clearance of the same blade uneven.

[0003] In order to ensure that the blade tip does not have local wear and tear, thereby reducing the life of the blade tip, it is often necessary to leave a larger safety gap at the blade tip. A larger tip gap will lead to an increase in tip leakage flow, affecting the overall aerodynamic performance of the turbine. Summary of the invention

[0004] An object of the present invention is to provide a method for designing cold blade tip clearance.

[0005] To achieve the above-mentioned purpose, a cold blade tip clearance design method comprises the following steps: S1. establishing a hot blade design model and a flow field grid, and making the hot blade design model have an equal tip clearance structure; S2. converting the hot blade design model into an initial cold blade model; S3. calculating the hot radial deformation of the blade tip using a computational fluid dynamics method; S4. obtaining a cold blade correction model by subtracting the hot radial deformation of the blade tip from the tip height of the hot blade design model.

[0006] In one or more embodiments, fluid-solid thermal coupling calculations are performed in the flow field grid, and a non-steady-state method is used to solve the blade temperature field, blade stress field, and blade deformation.

[0007] In one or more embodiments, a heat flow calculation is performed, and a steady-state method is used to solve the blade temperature field, blade stress field, and blade deformation.

[0008] In one or more embodiments, the method further includes step S5. Substituting the cold blade correction model obtained in step S4 into step S3, calculating the new blade tip hot radial deformation, and obtaining a new cold blade correction model.

[0009] In one or more embodiments, the method further comprises step S6. Repeating step S5 until the iteration result converges.

[0010] In one or more embodiments, a computational fluid dynamics method is used to calculate the amount of shroud required for blade adjustment, and in step S4, the cold initial model is adjusted according to the amount of shroud required for blade adjustment.

[0011] In one or more embodiments, the pitch angle of the blades is modified by adjusting the desired amount of shrouding of the blades.

[0012] In one or more embodiments, in step S2, the initial model of the cold blade is a structure with uneven distribution of blade tip and blade height.

[0013] The above-mentioned cold blade tip clearance design method calculates the local deformation of the turbine blade under the main working state, and reversely obtains the local height and surface shape of the blade tip in the cold state, thereby ensuring that the tip clearance is uniform under the working state of the blade, so as to further design the blade tip clearance as small as possible and reduce the leakage flow. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The above and other features, properties and advantages of the present invention will become more apparent through the following description in conjunction with the accompanying drawings and embodiments, in which:

[0015] Figure 1 is a flow chart of the cold blade tip clearance design method;

[0016] Figure 2 It is a flow chart of the steps for calculation using the fluid-heat coupling method;

[0017] Figure 3 It is a flow chart of the steps for calculation using the fluid-thermal-solid coupling method;

[0018] Figure 4 This is a top view of the blade tip;

[0019] Figure 5 It is a schematic diagram of the cold blade tip clearance design method.

[0020] Description of Reference Numerals

[0021] 100 Tip clearance

[0022] 105 Blades

[0023] 104 Turbine outer ring

[0024] 1051 Front Edge

[0025] 1052 trailing edge

[0026] 1053 Pressure side

[0027] 1054 Suction side DETAILED DESCRIPTION

[0028] The present invention is further described below in conjunction with specific embodiments and drawings. More details are elaborated in the following description to facilitate a full understanding of the present invention. However, the present invention can obviously be implemented in a variety of other ways different from the description herein. Those skilled in the art can make similar generalizations and deductions based on actual application situations without violating the connotation of the present invention. Therefore, the protection scope of the present invention should not be limited by the content of this specific embodiment.

[0029] It should be noted that these and other subsequent drawings are only examples and are not drawn to scale, and should not be used to limit the actual scope of protection required by the present invention.

[0030] Cold state blades refer to blades at room temperature, and hot state blades refer to blades at high temperature, that is, blades in working state.

[0031] In order to ensure that the tip clearance of hot blades in working condition is uniform, the cold tip clearance design method of moving blades disclosed in the present invention obtains cold blades with suitable tip height distribution from hot blades with uniform tip clearance through a hot-cold conversion method, so as to improve the uniformity of the tip clearance of the moving blades in working condition, and then design a smaller tip clearance of the moving blades to reduce tip leakage flow.

[0032] As reference Figure 5 As shown, there is a tip clearance 100 between the blade 105 and components such as the turbine outer ring 104. Under hot blade conditions, as shown in the simplified blade structure of the solid line, it is hoped that the tip clearance 100 is maintained at a uniform size N to reduce tip leakage flow. However, in actual work, the working environment of the turbine moving blades is high temperature, high pressure and high speed. Under the multiple effects of aerodynamic force, thermal load and centrifugal force, the moving blades will produce local deformation and stress. Due to the different forces at different parts of the blade tip, there are differences in local deformation. Therefore, when the blade changes from a cold state to a hot state, the tip clearance 100 cannot be guaranteed to be uniform as expected. Uneven tip clearance requires a larger safety gap to prevent the blade tip from rubbing, which leads to a larger leakage flow.

[0033] Therefore, the present application reversely designs a cold blade with different tip height distributions through a hot blade model with a uniform tip clearance of 100, as shown in the structure simplified by the dotted line. It is expected that the cold blade obtained according to the design scheme will have different tip heights H' in the natural state, and that the tip will be able to achieve a relatively consistent and uniform blade height H after being heated and deformed, thereby obtaining a uniform tip clearance distribution.

[0034] The method comprises the following steps: S1. establishing a hot design model of a blade and a flow field grid, and making the hot design model of the blade have an equal tip clearance structure; S2. converting the hot design model of the blade into an initial model of a cold blade; S3. using a computational fluid dynamics method (Computational Fluid Dynamics) to calculate the hot radial deformation of the blade tip, or directly calculating the cover amount required for blade adjustment; S4. using the tip height of the hot design model of the blade minus the hot radial deformation of the blade tip, adjusting the cold initial model according to the cover amount required for blade adjustment, and obtaining a corrected model of the cold blade.

[0035] In some embodiments, the method further includes steps S5 and S6: substituting the cold blade correction model obtained in step S4 into step S3, calculating the new blade tip hot radial deformation, and obtaining a new cold blade correction model; repeating step S5 until the iterative result converges. Considering the calculation accuracy and calculation resources, this step is an optional step.

[0036] Specifically, Figure 2 and Figure 3 Two calculation ideas are given: one is to perform fluid-heat calculation in step S3, and use the steady-state method to solve the blade temperature field, blade stress field and blade deformation; the other is to perform fluid-solid-thermal coupling calculation in the flow field grid in step S3, and use the unsteady-state method to solve the blade temperature field, blade stress field and blade deformation.

[0037] Fluid-heat coupling means that after the fluid domain and solid domain meshes are established, only the heat transfer between the fluid and the solid and the heat conduction inside the solid are calculated, and the temperature field of the solid domain is obtained as the temperature boundary condition during the finite element steady-state calculation of deformation. Fluid-heat-solid coupling means that after the fluid domain and solid domain meshes are established, the aerodynamic force, heat transfer process and solid deformation of the fluid are considered at the same time, and the unsteady-state method is used to solve. When calculating, unsteady calculation or steady calculation can be used for the aerodynamic boundary under a certain flight condition.

[0038] Specifically, in Figure 2 In the illustrated embodiment, firstly, based on the ideal condition of hot design, a hot design model of the blade with equal tip clearance is obtained, and the fluid domain and solid domain meshes are respectively established through fluid-heat coupling, and the temperature field of the solid domain of the blade is calculated. Subsequently, the hot model is initially converted from hot to cold state to the cold blade initial model. It can be understood that after the initial conversion, the cold blade initial model still has the characteristic of equal tip height. In some preferred embodiments, the staff can adjust the tip height distribution of the cold blade initial model based on experience, and correct the cold blade initial model to an uneven tip distribution structure in advance.

[0039] The finite element steady-state calculation method is used to calculate the stress field generated by the radial deformation and torsion of the blade caused by the blade temperature field and external forces such as centrifugal force and aerodynamic force, and the corresponding shroud amount that needs to be adjusted and the local hot radial deformation of the blade after the shroud amount is adjusted are calculated.

[0040] The purpose of adjusting the blade shroud is to achieve the best compensation of the centrifugal bending moment to the aerodynamic bending moment without changing the blade shape and the blade body dimensions. Therefore, considering the shroud adjustment can avoid stress concentration at the blade root and achieve compensation for the circumferential external force on the blade. By adjusting the required shroud amount of the blade, the inclination angle of the blade relative to the circumferential direction is corrected. This inclination angle refers to Figure 4 The angle of each blade 105 relative to the up and down direction.

[0041] Then, the corresponding hot radial deformation is subtracted from the design value of the hot radial height of the moving blade in each area to obtain the cold radius of each area of ​​the blade tip, and further obtain the cold variable clearance blade tip, that is, the cold blade correction model.

[0042] Furthermore, the obtained cold blade correction model is substituted into the above calculation steps to perform one or more finite element steady-state iterative calculations to check and correct the relevant cover adjustment and hot radial deformation until the results converge, and the final cold moving blade model and cold moving blade tip clearance are obtained. This model can be used as the design target.

[0043] The calculation process of the above method is direct, fast and easy to implement.

[0044] exist Figure 3 In the illustrated embodiment, a hot design model of a blade with equal tip clearance is first obtained based on the ideal condition of hot design, and then a preliminary hot-cold conversion is performed based on the assumed hot design model of the blade with equal tip clearance to obtain an initial model of the cold blade.

[0045] Subsequently, the fluid domain and solid domain meshes are established respectively, and the aerodynamic force, heat transfer process and solid deformation of the fluid are considered at the same time. Through the fluid-thermal-solid coupling method and unsteady calculation, the stress and deformation of the moving blade in each area and direction are obtained, so as to calculate the corresponding shroud amount that needs to be adjusted for the blade and the local hot radial deformation of the blade tip after the shroud amount is adjusted.

[0046] Then, the initial design value of the hot radial height of the moving blade in each area is used, and the radial height of the hot design model of the blade is subtracted from the corresponding hot radial deformation to obtain the cold radius of each area of ​​the blade tip, the cold variable gap blade tip, and the corrected cold blade model after a correction.

[0047] Furthermore, the latest cold blade correction model is used to perform one or more iterations of the fluid-thermal-solid coupling unsteady calculation to check and correct the relevant shroud adjustment and hot radial deformation. In practical applications, this step can also be omitted as appropriate.

[0048] The model and calculation of the above method are closer to reality and can obtain more accurate results.

[0049] The radial deformation calculated by the above two methods does not necessarily change linearly from the leading edge 1051 to the trailing edge 1052 of the blade tip, such as Figure 4 As shown. Moreover, at the same axial position, there may be a slight difference in the radial deformation of the pressure side 1053 and the suction side 1054. At the same time, it is necessary to consider that these deformations will also be different when the engine is in a transition state such as acceleration and deceleration, but the overall trend is similar. Therefore, in actual application, the distribution of the optimal cold tip clearance needs to be comprehensively considered based on the processing and manufacturing conditions and the transition state analysis conditions.

[0050] Therefore, the above method calculates the local deformation of the turbine blades in the main working state, and inversely calculates the local height and surface shape of the blade tip in the cold state, thereby ensuring that the blade tip clearance is uniform in the working state of the blade, reducing the risk of blade tip collision and wear, and can also design the blade tip clearance as small as possible to reduce the leakage flow. This method is applicable to similar working environments of different models, and can be used as a general process for the cold state clearance design of the blade tip, so that the blade tip clearance of the same blade in the working state tends to be uniform, so as to minimize the blade tip clearance.

[0051] The present application uses specific words to describe the embodiments of the present application. For example, "one embodiment", "an embodiment", and / or "some embodiments" refer to a certain feature, structure or characteristic related to at least one embodiment of the present application. Therefore, it should be emphasized and noted that "one embodiment" or "an embodiment" or "an alternative embodiment" mentioned twice or multiple times in different positions in this specification does not necessarily refer to the same embodiment. In addition, some features, structures or characteristics in one or more embodiments of the present application can be appropriately combined.

[0052] Although the present invention is disclosed as above with preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art may make possible changes and modifications without departing from the spirit and scope of the present invention. Therefore, any modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention shall fall within the protection scope defined by the claims of the present invention.

Claims

1. A cold blade tip clearance design method, characterized in that: The steps include: S1. Establishing a blade thermal design model and a flow field grid, and making the blade thermal design model have an equal tip clearance structure; S2. converting the hot blade design model into a cold blade initial model; S3. Calculate the radial deformation of the blade tip in hot state using computational fluid dynamics method; S4. Using the tip height of the hot design model of the blade minus the hot radial deformation of the blade tip, a cold blade correction model is obtained.

2. The method according to claim 1, characterized in that In step S3, fluid-solid thermal coupling calculation is performed in the flow field grid, and the blade temperature field, blade stress field and blade deformation are solved using a non-steady-state method.

3. The method according to claim 1, characterized in that In step S3, heat flow calculation is performed, and the blade temperature field, blade stress field and blade deformation are solved using a steady-state method.

4. The method according to any one of claims 1 to 3, characterized in that: The method also includes step S5. Substituting the cold blade correction model obtained in step S4 into step S3, calculating the new blade tip hot radial deformation, and obtaining a new cold blade correction model.

5. The method according to claim 4, characterized in that The method further comprises step S6, repeating step S5 until the iterative result converges.

6. The method according to claim 1, characterized in that In step S3, a computational fluid dynamics method is used to calculate the amount of shrouding required for blade adjustment, and in step S4, the cold initial model is adjusted according to the amount of shrouding required for blade adjustment.

7. The method according to claim 6, characterized in that The inclination angle of the blade is corrected by adjusting the required shroud amount through the blade.

8. The method according to claim 1, characterized in that In step S2, the initial model of the cold blade is a structure with uneven distribution of blade tip and blade height.

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