Fan blade stress calculation method

Abstract

A fan blade stress calculation method is provided, comprising the following steps: S1. applying a load to an engine whole machine model, performing static strength calculation, and obtaining a calculation result of the engine whole machine model; S2. picking up boundary displacement amounts at a fan sub-model region in the calculation result of the engine whole machine model; S3. linearly scaling the load, repeating steps S1-S2, and obtaining multiple boundary displacement amounts under different load conditions; S4. performing static strength calculation on the fan sub-model region under different load conditions, and obtaining sizes of support reaction forces and / or support reaction torques of a front mounting section under multiple load conditions; and S5. obtaining a load condition when the support reaction force of the front mounting section is 0 and stress distribution of the fan sub-model region under the load condition. The above method can obtain more accurate fan blade stress distribution.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of aero-engines, in particular to the field of stress analysis methods. BACKGROUND

[0002] The load-bearing frame is the backbone of the aero-engine, which plays a role in transmitting working load, limiting load and special working condition load. A typical aero-engine sets the main mounting joint at the 12 o'clock direction of the turbine rear casing, and sets a front auxiliary mounting joint on the outer ring of the intermediate casing. Under normal aerodynamic load conditions, the axial force is transmitted to the main mounting joint through the intermediate casing and the thrust rod, and the torque is transmitted to the main mounting joint through the compressor casing, the combustion chamber casing and the turbine casing. For a high-bypass-ratio turbofan engine, the fan blades and fan outlet guide vanes can generate a large torque, so it is necessary to ensure that the entire torque transmission path meets the strength margin requirements.

[0003] The load-bearing frame of the intermediate casing of a common aero-engine adopts a design feature of fusion of the main support plate and the fan outlet guide vane (OGV). The main support plate plays a role in transmitting load, and the outlet guide vane plays a role in flow regulation. At present, advanced aero-engines in the world have cancelled the structure feature of a large independent support plate behind the fan, and instead adopted the fusion design of the fan OGV and the support plate. The fusion designed support plate and OGV blade not only play a role in transmitting load and bearing, but also serve as an outlet flow guide. Under the same thrust level, it has a lighter weight.

[0004] In addition, safety is a basic requirement of aero-engines, and all fusion designed OGV support plate structures need to ensure their structural strength safety under the dual functions of load bearing and flow regulation. Safety and lightweight design are contradictory opposites.

[0005] Since the aero-engine is installed on the aircraft in a 12 o'clock position, the fan OGV blade will cause the overall engine to produce a rollover deformation under the action of a large aerodynamic torque. This deformation is essentially a kind of asymmetric deformation, which needs to be fully simulated in the overall numerical model. However, due to the complexity of the structure and too many component features, the overall numerical model cannot fully express all the geometric features of interest. The overall numerical model often simplifies the fan OGV blade with shell elements or simplified solid elements, and applies a load in the form of equivalent torque. This simplification and load method cannot accurately assess the local stress of the fan OGV blade.

[0006] The above problems are often solved by using a separate sub-model calculation method in engineering, however, the load results of the equivalent torque application are not completely consistent with the case under the fan OGV aerodynamic force bearing, which leads to inaccurate sub-model boundary derived from the whole machine model under the specified calculation condition. The results calculated by the sub-model method often have large errors. SUMMARY

[0007] An object of the present application is to provide a fan blade stress calculation method capable of obtaining more accurate fan blade stress distribution.

[0008] To achieve the above object, the fan blade stress calculation method is used to calculate the fan blade of an aero-engine, the aero-engine further comprising a front mounting section and a rear mounting section, the method comprising the following steps: S1. applying a load to an engine whole machine model to perform static strength calculation to obtain calculation results of the engine whole machine model; S2. picking up boundary displacement amounts at a fan sub-model region in the calculation results of the engine whole machine model; S3. linearly scaling the load, repeating steps S1-S2 to obtain multiple boundary displacement amounts under different load conditions; S4. performing static strength calculation on the fan sub-model region under the different load conditions to obtain sizes of the front mounting section counterforce and / or counter-torque under the multiple load conditions; and S5. obtaining a load condition when the counterforce of the front mounting section is 0 and stress distribution of the fan sub-model region under the load condition.

[0009] In one or more embodiments, a relationship curve between the counterforce of the front mounting section and the load condition is obtained, and the load condition when the counterforce of the front mounting section is 0 is obtained in the relationship curve.

[0010] In one or more embodiments, a fitting equation is obtained according to the relationship curve between the counterforce of the front mounting section and the load condition, and the load condition when the counterforce of the front mounting section is 0 is calculated according to the fitting equation.

[0011] In one or more embodiments, the linear scaling factor when the boundary displacement amount is linearly scaled comprises a linear factor greater than or equal to 1 and a linear factor less than 1.

[0012] In one or more embodiments, the boundary displacement is linearly scaled to obtain five interpolation boundary displacements of 80%, 90%, 100%, 110% and 120%.

[0013] In one or more embodiments, five load conditions are calculated according to the five interpolation boundary displacements.

[0014] In one or more embodiments, the static strength calculation of the engine whole machine model and the fan sub-model is performed by using a computational fluid dynamics method.

[0015] The method utilizes the feature that the front mounting joint assembly does not transfer axial force and torque under normal aerodynamic load, confirms the accuracy of simulation values, and obtains stress distribution when the support reaction force is 0 through linearly changing load and boundary displacement, so that the accuracy of the blade stress distribution can be significantly improved. BRIEF DESCRIPTION OF DRAWINGS

[0016] The above and other features, properties, and advantages of the present application will become more apparent by referring to the following description in conjunction with the accompanying drawings, in which:

[0017] Figure 1 is a schematic diagram of an overall layout of an aero-engine mounting system;

[0018] Figure 2 is a schematic diagram of a front mounting joint assembly;

[0019] Figure 3 is a flowchart of a fan blade stress calculation method;

[0020] Figure 4A is a schematic diagram of displacement scaling;

[0021] Figure 4B is a curve diagram of support reaction force of the front mounting joint varying with load conditions;

[0022] Figure 5 is a support reaction force distribution diagram of the front mounting joint;

[0023] Figure 6 is a titanium alloy OGV stress distribution diagram in the 12 o'clock direction;

[0024] Figure 7 is a front mounting joint connecting rod calculation result;

[0025] Figure 8 is a flowchart of a specific embodiment of the fan blade stress calculation method. DETAILED DESCRIPTION

[0026] The present application will be further described below in conjunction with specific embodiments and the accompanying drawings, and more details are set forth in the following description in order to fully understand the present application, but the present application can certainly be implemented in various other ways different from the description, and those skilled in the art can make similar generalizations and deductions according to actual application conditions without departing from the connotation of the present application, so the protection scope of the present application should not be limited by the content of the specific embodiments.

[0027] It should be noted that these and other subsequent drawings are only examples, are not drawn according to the condition of equal proportion, and should not be used as a limitation on the actual protection scope required by the present application.

[0028] The overall layout of the engine mounting system is shown in Figure 1 The thrust generated by the engine body 30 is mainly transmitted to the rear mounting lug assembly 20 through the thrust link, and the torque of the fan OGV is mainly transmitted to the front mounting lug assembly 10 through the intermediate casing, the compressor casing, the turbine casing, etc. Under normal aerodynamic load conditions, the front mounting lug assembly 10 does not transmit axial force and torque.

[0029] The side view, top view and front view of the front mounting lug assembly 10 are shown in Figure 2 From the perspective of structural design, the middle of the front mounting lug assembly is a broken safety hole, and under normal aerodynamic load conditions, there is a gap of about 10 mm at this position, which does not transmit force and torque, and the remaining left and right connecting rods are a typical unstable trapezoidal structure that can rotate around the fulcrum with a ball joint. Therefore, the above structural design features make the front mounting lug assembly not transmit axial force and torque under normal aerodynamic load, becoming a quadrilateral structure that does not transmit axial force and torque.

[0030] Therefore, when simulated using computational fluid dynamics methods, the support reaction force of the front mounting lug assembly 10 being 0 indicates that the front mounting lug assembly 10 does not transmit axial force and torque, so the simulation data can be characterized as relatively accurate; when the support reaction force of the front mounting lug assembly obtained from the simulation data is not 0, it deviates from the design under normal aerodynamic load conditions, so the current simulation data is considered relatively inaccurate.

[0031] Based on this, the fan blade stress calculation method disclosed in the present disclosure uses the support reaction force of the front mounting lug assembly as a standard to judge the accuracy of the simulation results, and then obtains relatively accurate calculation data of the fan blade bearing force, stress, etc., providing accurate guidance data for the design of the fan blade.

[0032] Referring to Figure 3 and Figure 8 The method comprises the following steps: S1. applying a load to an engine whole machine model to perform static strength calculation and obtain a calculation result of the engine whole machine model; S2. picking up a boundary displacement amount at a fan sub-model region in the calculation result of the engine whole machine model; S3. linearly scaling the load, repeating steps S1-S2 to obtain a plurality of boundary displacement amounts under different load conditions; S4. performing static strength calculation on the fan sub-model region under the different load conditions to obtain the support reaction force and / or support reaction torque of the front mounting lug under the plurality of load conditions; and S5. obtaining a load condition when the support reaction force of the front mounting lug is 0 and a stress distribution of the fan sub-model region under the load condition.

[0033] Specifically, in step S1, an engine overall calculation model and parameters are prepared, the engine overall calculation model including a compressor, a turbine, a combustion chamber, a casing, a fan, a front mounting assembly, a rear mounting assembly and the like, specifically including an overall finite element model, a torque load, material parameters, a freedom degree constraint position and a manner and the like. A computational fluid dynamics method is used to perform static strength calculation on the engine overall model.

[0034] Generally, a maximum aerodynamic load condition is selected to perform stress analysis, such as a condition of maximum torque.

[0035] An engine overall numerical model is used to perform static strength calculation, and 100% load condition, i.e. maximum aerodynamic load condition, is used to obtain static strength data, displacement deformation and the like of the engine overall model.

[0036] In step S2, the calculation results of the engine overall model are post-processed to obtain boundary displacement of the fan sub-model under the 100% load condition. The fan sub-model is a refined fan area selected from the overall calculation model, including a casing, an inlet guide vane (OGV), a hub and the like, and can more finely obtain force distribution of each blade of the fan.

[0037] In step S3, the load is linearly scaled, and the linear scaling coefficient includes a linear coefficient greater than or equal to 1 and a linear coefficient less than 1. For example, 80%, 90%, 100%, 110% and 120% load conditions are obtained by linear scaling, and different boundary displacements under the five load conditions are obtained. The boundary displacement is used to define the area of the sub-model.

[0038] In step S4, the calculation model and parameters of the fan sub-model are prepared, such as an intermediate force-bearing frame finite element model, fan OGV aerodynamic load, material parameters and the aforementioned multiple interpolation boundary displacements. Then, finite element static strength calculation is performed on the fan sub-model to obtain the size of the support reaction force and / or support reaction torque under the 80%, 90%, 100%, 110% and 120% load conditions.

[0039] Since the overall static strength calculation is a linear elastic calculation process, according to the finite element calculation theory, when the stiffness matrix remains unchanged, i.e. the calculation model is consistent, the displacement result is proportional to the load at this time. Therefore, it is feasible to obtain five interpolation boundary displacements under five load conditions by linear scaling.

[0040] For example, in one embodiment, the calculation results under two torque conditions of minimum aerodynamic load (take-off state) and maximum aerodynamic load are compared, and the load torque is shown in Table 1 below, and the proportional relationship of the load torque under maximum load and minimum load can be obtained.

[0041] Table 1 calculates the contrast working condition

[0042]

[0043] At the same time, the interpolation boundary displacement structure under two working conditions can be extracted, and the displacement scaling ratio relationship shown in Figure 4A is obtained. Figure 4A The horizontal coordinate represents the data point number, and the vertical coordinate represents the boundary displacement proportion. The results show that, starting from theoretical analysis and finite element practice analysis, the linear scaling of the result displacement can represent the interpolation boundary displacement under 80%, 90%, 100%, 110%, and 120% load working conditions.

[0044] Subsequently, the fan sub-model, that is, the fan OGV force-bearing frame component calculation results are post-processed to obtain the front mounting section assembly, that is, the front auxiliary mounting section connecting rod counter-axial force and counter-torque data under 80%, 90%, 100%, 110%, and 120% load working conditions.

[0045] According to the front mounting section counter-axial force data under 80%, 90%, 100%, 110%, and 120% load working conditions, the relationship curve of the front mounting section counter-force and the load working condition is obtained, and the load working condition when the front mounting section counter-force is 0 is obtained in the relationship curve.

[0046] Or further, according to the relationship curve of the front mounting section counter-force and the load working condition, a fitting equation is obtained, the load working condition value when the front mounting section counter-force is 0 is calculated according to the equation, and the counter-torque is verified. As shown in Figure 4B , through the fitting equation A, y = 24692x - 41536, where x is the load percentage gama value, y is the counter-force size, and the counter-torque is represented by the left vertical coordinate axis and the right vertical coordinate. According to the equation, the load percentage gama value when the front section counter-axial force is equal to 0 is calculated, and the load working condition value is obtained by back calculation. The load percentage gama value represents the load proportion, for example, under 90% load working condition, the gama value is 0.9.

[0047] According to the equation, the load percentage gama value when the front section counter-axial force is equal to 0 is calculated, and the counter-torque is verified. The curve diagram drawn is shown in Figure 4B , the calculated gama = 1.682, that is, under 168.2% load, the counter-force is 0, and the corresponding torque is -516 N.mm, the loading torque is 257560000 N.m, and the calculated counter-torque proportion is very small, so the gama value is considered appropriate.

[0048] When the calculated load working condition value when the counter-force is 0 is not in the aforementioned linear difference obtained 80%, 90%, 100%, 110%, and 120% load working conditions, such asFigure 4B As shown, finite element static strength analysis of the fan submodel is carried out again, and the load is the numerical value of the 168.2% load working condition calculated in the foregoing step. The submodel data under the load working condition are calculated, the counteracting axial force and counteracting torque of the front mounting joint connecting rod are extracted, and rationality check is performed.

[0049] If the extracted counteracting axial force of the front joint is approximately equal to 0 and the counteracting torque is small, it is considered that the calculation result is reasonable, the current simulation data can represent a relatively accurate state, and the calculation is ended. If the extracted counteracting axial force of the front joint is large and the counteracting torque is large, it is considered that the calculation result is unreasonable, and the whole machine calculation model needs to be rechecked.

[0050] As shown, the static strength analysis of the fan OGV load-bearing frame under the condition of gama=1.682, i.e., 168.2% load working condition, the counteracting force result of the front mounting joint connecting rod is as shown in Figure 7 As shown, FZ represents the axial size, and MZ represents the torque size. The deformation result of the fan OGV load-bearing frame is as shown in Figure 5 As shown, the 12 o'clock titanium OGV stress distribution is as shown in Figure 8 The counteracting force of the front joint connecting rod is small, and the deformation and stress distribution result is reasonable, so the above calculation result can reflect the stress distribution under formal loading.

[0051] By performing the above method, the problem that the whole machine numerical calculation model cannot examine the local stress of the fan OGV and the large error of the fan OGV stress analysis result caused by the inaccurate submodel boundary can be solved, so that the fan OGV stress analysis result can be more accurately obtained, the strength safety examination is supported, so that the fan OGV reference configuration can be reliably determined in the design stage, the type development risk is greatly reduced, the development cycle is saved, and the waste of trial production result is avoided.

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

Claims

1. A method for calculating the stress of fan blades, used to calculate the stress of fan blades in an aero-engine, wherein the aero-engine further includes a front mounting section and a rear mounting section, characterized in that, Includes the following steps: S1. Apply load to the engine model and perform static strength calculation to obtain the calculation results of the engine model; S2. Select the boundary displacement of the fan sub-model region from the calculation results of the engine whole model; S3. Scaling the load linearly, repeating steps S1-S2, to obtain multiple boundary displacements under different load conditions. S4. Perform static strength calculations on the fan sub-model area under the different load conditions to obtain the magnitude of the support reaction force and the magnitude of the support reaction torque of the front mounting section under the multiple load conditions; S5. Obtain the relationship curve between the support reaction force of the front mounting section and the load condition. Obtain the fitting equation based on the relationship curve between the support reaction force of the front mounting section and the load condition. Calculate the load condition when the support reaction force of the front mounting section is 0 based on the fitting equation, and verify the support reaction torque to obtain the stress distribution of the fan sub-model area under the load condition.

2. The fan blade stress calculation method as described in claim 1, characterized in that, The linear scaling factor when linearly scaling the boundary displacement includes linear coefficients greater than or equal to 1 and linear coefficients less than 1.

3. The fan blade stress calculation method as described in claim 2, characterized in that, The boundary displacement is linearly scaled to obtain five interpolated boundary displacements of 80%, 90%, 100%, 110%, and 120%.

4. The fan blade stress calculation method as described in claim 3, characterized in that, Five load conditions are calculated based on the five interpolated boundary displacements.

5. The method for calculating fan blade stress as described in claim 1, characterized in that, Computational fluid dynamics methods were used to perform static strength calculations on the engine whole model and the fan sub-model.

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