Fan blade stress calculation method

Abstract

The invention provides a fan blade stress calculation method which comprises the following steps: S1, applying a load to an engine complete machine model, and carrying out static strength calculation to obtain a calculation result of the engine complete machine model; s2, selecting a boundary displacement amount at a fan sub-model area in a calculation result of the engine complete machine model; s3, carrying out linear scaling on the load, and repeating the steps S1 to S2 to obtain a plurality of boundary displacements under different load working conditions; s4, static strength calculation is conducted on the fan sub-model area under different load working conditions, and the bearing reaction force and / or bearing reaction torque of the front installation joint under the multiple load working conditions are / is obtained; and S5, obtaining the load working condition when the bearing reaction of the front mounting section is 0 and the stress distribution of the fan sub-model area under the load working condition. According to the method, more accurate fan blade stress distribution can be obtained.

Description

Technical Field

[0001] The present invention relates to the field of aero engines, and in particular to the field of stress analysis methods. Background Art

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

[0003] The common aircraft engine intermediate casing load-bearing frame adopts the design feature of the fusion of the main support plate and the fan outlet guide vane (Outlet Guide Vane). The main support plate plays the role of transferring loads, and the outlet guide vane plays the role of rectification. At this stage, most of the advanced aircraft engines in the world have cancelled the structural feature of the independent large support plate behind the fan, and replaced it with the fusion design of the fan OGV and the support plate. The fusion-designed support plate and OGV blades not only play the role of transferring loads, but also serve as the outlet guide function. At the same thrust level, it has a lighter weight.

[0004] In addition, safety is a basic requirement for aircraft engines, and all integrated OGV support plate structures need to ensure their structural strength and safety under the dual functions of load bearing and rectification. Safety and lightweight design are contradictory opposites.

[0005] Since the aircraft engine is installed on the aircraft in a suspended manner at the 12 o'clock position, the fan OGV blades will cause the entire engine to flip and deform under the action of the atmospheric dynamic torque. This deformation is essentially an asymmetric deformation and needs to be fully simulated in the numerical model of the whole machine. However, due to the complexity of the structure and too many component features, the numerical model of the whole machine cannot fully express all the geometric features of concern. The numerical model of the whole machine often simplifies the fan OGV blades with shell units or simplified solid units, and applies loads in the form of equivalent torque. This simplification method and load method cannot accurately assess the local stress of the fan OGV blades.

[0006] In engineering, a separate sub-model calculation method is often used to solve the above problem. However, since the load results applied by the equivalent torque are not completely consistent with the situation under the aerodynamic load of the fan OGV, this leads to inaccurate sub-model boundaries derived from the whole machine model under the specified calculation conditions. The results calculated using the sub-model method often have large errors. Summary of the invention

[0007] An object of the present invention is to provide a fan blade stress calculation method that can obtain a more accurate fan blade stress distribution.

[0008] To achieve the above-mentioned destination, the fan blade stress calculation method is used to calculate the fan blades of an aircraft engine, wherein the aircraft engine also includes a front mounting node and a rear mounting node. The method includes the following steps: S1. Applying a load to the engine whole machine model, performing a static strength calculation, and obtaining a calculation result of the engine whole machine model; S2. Picking the boundary displacement at the fan sub-model area in the calculation result of the engine whole machine model; S3. Linearly scaling the load, repeating steps S1-S2, and obtaining multiple boundary displacements under different load conditions; S4. Performing a static strength calculation on the fan sub-model area under the different load conditions, and obtaining the support reaction force and / or support reaction torque of the front mounting node under the multiple load conditions; S5. Obtaining the load condition when the support reaction force of the front mounting node is 0 and the stress distribution of the fan sub-model area under the load condition.

[0009] In one or more embodiments, a relationship curve between the support reaction force of the front installation joint and the load condition is obtained, and the load condition when the support reaction force of the front installation joint is 0 is obtained within the relationship curve.

[0010] In one or more embodiments, a fitting equation is obtained based on a relationship curve between the support reaction force of the front installation node and the load condition, and the load condition when the support reaction force of the front installation node is 0 is calculated based on the fitting equation.

[0011] In one or more embodiments, the linear scaling coefficient when linearly scaling the boundary displacement includes a linear coefficient greater than or equal to 1 and a linear coefficient less than 1.

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

[0013] In one or more embodiments, five load conditions are calculated based on the five interpolated boundary displacements.

[0014] In one or more embodiments, computational fluid dynamics methods are used to perform static strength calculations on the engine full machine model and the fan sub-model.

[0015] The above method uses the characteristic that the front mounting node assembly does not transmit axial force and torque under normal aerodynamic loads to confirm the accuracy of the simulation values, and calculates the stress distribution when the support reaction force is 0 by linearly changing the load and boundary displacement. This correction method can significantly improve the accuracy of the blade stress distribution. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] 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:

[0017] Figure 1 It is a schematic diagram of the overall layout of the aircraft engine installation system;

[0018] Figure 2 is a schematic diagram of the front installation section assembly;

[0019] Figure 3 is a flow chart of the fan blade stress calculation method;

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

[0021] Figure 4B It is a curve diagram showing the change of the support reaction force of the front installation section with the load condition;

[0022] Figure 5 It is the reaction force distribution diagram of the front installation node;

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

[0024] Figure 7 It is the calculation result of the front mounting joint connecting rod;

[0025] Figure 8 It is a flow chart of a specific embodiment of a fan blade stress calculation method. DETAILED DESCRIPTION

[0026] 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.

[0027] 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.

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

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

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

[0031] Based on this, the fan blade stress calculation method described in the present invention uses the support reaction force of the previously installed node assembly as the verification standard to judge the accuracy of the simulation results, and then obtain relatively accurate calculation data such as the fan blade bearing capacity and stress, providing accurate guidance data for the design of fan blades.

[0032] Reference Figure 3 and Figure 8 As shown, the method includes the following steps: S1. Applying a load to the engine whole machine model, performing a static strength calculation, and obtaining a calculation result of the engine whole machine model; S2. Picking the boundary displacement at the fan sub-model area in the calculation result of the engine whole machine model; S3. Linearly scaling the load, repeating steps S1-S2, and obtaining multiple boundary displacements under different load conditions; S4. Performing a static strength calculation on the fan sub-model area under the different load conditions, and obtaining the support reaction force and / or support reaction torque of the front mounting node under the multiple load conditions; S5. Obtaining the load condition when the support reaction force of the front mounting node is 0 and the stress distribution of the fan sub-model area under the load condition.

[0033] Specifically, in step S1, the whole engine calculation model and parameters are prepared, and the whole engine calculation model includes components such as compressor, turbine, combustion chamber, casing, fan, front mounting section assembly, rear mounting section assembly, etc., and specifically includes whole engine finite element model, torque load, material parameters, degree of freedom constraint position and method, etc. The static strength calculation of the whole engine model is performed using computational fluid dynamics method.

[0034] Generally, the maximum aerodynamic load condition is selected for stress analysis, such as the condition with the maximum torque as the specific parameter.

[0035] The static strength calculation is carried out using the numerical model of the whole engine. The 100% load condition, i.e. the maximum aerodynamic load condition, is used to obtain the static strength data, displacement deformation and other calculation results of the whole engine model.

[0036] In step S2, the calculation results of the engine whole machine model are post-processed to obtain the boundary displacement of the fan sub-model under 100% load conditions. The fan sub-model is a refined fan area selected from the whole machine calculation model, including the casing, inlet guide vanes OGV, hub and other components, which can obtain the force distribution of each fan blade in a more detailed manner.

[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, through linear scaling, five load conditions of 80%, 90%, 100%, 110%, and 120% are obtained, and different boundary displacements under the five load conditions are obtained. The boundary displacement is used to limit the area of ​​the submodel.

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

[0039] Since the static strength calculation of the whole machine is a linear elastic calculation process, according to the finite element calculation theory, when the stiffness matrix remains unchanged, that is, the calculation model is consistent, the displacement result is proportional to the load. 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 torques at minimum aerodynamic load (takeoff state) and maximum aerodynamic load are compared, and the load torque is shown in Table 1 below, so that the proportional relationship between the load torque under maximum load and minimum load can be obtained.

[0041] Table 1 Calculation comparison conditions

[0042]

[0043] At the same time, the interpolation boundary displacement structure under the two working conditions can be extracted to obtain Figure 4A Displacement scaling relationship shown. Figure 4A The horizontal axis represents the data point number, and the vertical axis represents the ratio of the boundary displacement. The result shows that, based on theoretical analysis and finite element practical analysis, the linear scaling method of the result displacement can characterize the interpolated boundary displacement under five load conditions of 80%, 90%, 100%, 110%, and 120%.

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

[0045] According to the axial reaction force data of the front installation node under load conditions of 80%, 90%, 100%, 110%, and 120%, the relationship curve between the support reaction force of the front installation node and the load condition is obtained, and the load condition when the support reaction force of the front installation node is 0 is obtained within the relationship curve.

[0046] Or further, a fitting equation is obtained based on the relationship curve between the support reaction force of the front installation section and the load condition, and the load condition value when the support reaction force of the front installation section is 0 is calculated based on the equation, and the support reaction torque is tested. Figure 4B As shown, by fitting equation A, y=24692x-41536, where x is the load percentage gama value, y is the size of the support reaction force, and the left ordinate axis represents the support reaction torque. According to the equation, the load percentage gama value at the front section support reaction axial force equals 0, and the load condition value is obtained by reverse calculation. The load percentage gama value represents the load ratio. For example, for a 90% load condition, the gama value is 0.9.

[0047] According to the equation, calculate the load percentage gama value when the anti-axial force of the front section is equal to 0, and check the anti-torque of the support. The curve diagram is as follows Figure 4B As shown, the inverse calculation shows gama=1.682, that is, under 168.2% load, the support reaction force is 0, the corresponding torque is -516N.mm, and the loading torque is 257560000N.m. The calculated support reaction torque accounts for a very small proportion, and it is considered that the gama value is appropriate.

[0048] When the load condition value when the calculated support reaction force is 0 is not within the 80%, 90%, 100%, 110%, 120% load conditions obtained by the aforementioned linear difference, such as Figure 4B As shown, the finite element static strength analysis is performed on the fan sub-model again. The load at this time is the 168.2% load condition value calculated in the previous step. The sub-model data under this load condition is calculated, the anti-axial force and anti-torque of the front installation section connecting rod are extracted, and the rationality is checked.

[0049] If the extracted anti-axial force of the front section branch is approximately equal to 0 and the anti-torque of the branch is very small, the calculation result is considered reasonable and can represent that the current simulation data is relatively accurate, and the calculation ends. If the extracted anti-axial force of the front section branch is large and the anti-torque of the branch is large, the calculation result is considered unreasonable and the whole machine calculation model needs to be rechecked.

[0050] If gama=1.682, i.e. 168.2% load condition, the static strength analysis of the fan OGV bearing frame, the corresponding front installation section connecting rod support reaction result is as follows Figure 7 As shown in the figure, FZ represents the axial size and MZ represents the torque size. The deformation results of the fan OGV load-bearing frame are shown in the figure below. Figure 5 As shown, the stress distribution of titanium alloy OGV at 12 o'clock is as follows Figure 8 The support reaction force of the front connecting rod is very small, and the deformation and stress distribution results are reasonable. Therefore, the above calculation results can reflect its stress distribution under formal loading.

[0051] By executing the above method, the problem that the numerical calculation model of the whole machine cannot assess the local stress of the fan OGV and the fan OGV stress analysis result has a large error caused by inaccurate sub-model boundaries can be solved, thereby obtaining the fan OGV stress analysis result more accurately, providing support for strength and safety assessment, and reliably determining the fan OGV reference configuration in the design stage, greatly reducing the model development risk, saving the development cycle and avoiding the waste of trial production results.

[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 fan blade stress calculation method, used for calculating a fan blade of an aircraft engine, wherein the aircraft engine further comprises a front mounting section and a rear mounting section, and is characterized in that: The steps include: S1. Applying a load to the whole engine model, performing a static strength calculation, and obtaining a calculation result of the whole engine model; S2. picking the boundary displacement of the fan sub-model region in the calculation result of the whole engine model; S3. Linearly scale the load and repeat steps S1-S2 to obtain multiple boundary displacements under different load conditions; S4. Perform 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 section under the multiple load conditions; S5. Obtain the load condition when the support reaction force of the front installation node is 0 and the stress distribution of the fan sub-model area under the load condition.

2. The fan blade stress calculation method according to claim 1, characterized in that: A relationship curve between the support reaction force of the front installation joint and the load condition is obtained, and the load condition when the support reaction force of the front installation joint is 0 is obtained within the relationship curve.

3. The fan blade stress calculation method according to claim 2, characterized in that: A fitting equation is obtained according to a relationship curve between the support reaction force of the front installation joint and the load condition, and the load condition when the support reaction force of the front installation joint is 0 is calculated according to the fitting equation.

4. The fan blade stress calculation method according to claim 1, characterized in that: The linear scaling coefficient when linearly scaling the boundary displacement includes a linear coefficient greater than or equal to 1 and a linear coefficient less than 1.

5. The fan blade stress calculation method according to claim 4, characterized in that: The boundary displacement is linearly scaled to obtain five interpolated boundary displacements of 80%, 90%, 100%, 110%, and 120%.

6. The fan blade stress calculation method according to claim 5, characterized in that: Five load conditions are calculated based on the five interpolated boundary displacements.

7. The fan blade stress calculation method according to claim 1, characterized in that: Computational fluid dynamics methods are used to perform static strength calculations on the engine model and fan sub-model.

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