Finite element method-based variable cycle engine complete machine dynamics analysis method

Abstract

The invention relates to the technical field of aero-engine complete machine dynamics analysis, and discloses a variable cycle engine complete machine dynamics analysis method based on a finite element method.The method specifically comprises the following steps that firstly, a high-precision variable cycle complete machine finite element model is established, and the high-precision complete machine finite element model is established by adopting a step-by-step modeling thought; 2, complete machine response calculation: inputting an engine excited mathematical representation model into a complete machine finite element model, and establishing an aero-engine complete machine high-precision finite element model through a distributed model correction strategy, so that the aero-engine complete machine high-precision finite element model can reflect the actual engine working condition; and then, the excited mathematical representation model of the engine is input to the established high-precision finite element model, so that the response of the engine in a working environment can be effectively predicted, the performance and reliability of the engine are pre-judged and optimized, and the manpower and test equipment resource cost of the whole machine test of the variable cycle engine are saved.

Description

Technical Field

[0001] The present invention relates to the technical field of aircraft engine whole machine dynamics analysis, and in particular to a variable cycle engine whole machine dynamics analysis method based on the finite element method. Background Art

[0002] Vibration is one of the main causes of aircraft engine failures and is directly related to the safe and stable operation of the engine. Compared with traditional aircraft engines, the new generation of variable cycle engines usually adopts a three-rotor, multi-duct design to improve thrust and efficiency. The development of these technologies has significantly improved the performance and fuel efficiency of the engine, but it has also brought more complex dynamic behaviors and a more complex load environment. Traditional analysis methods are difficult to cope with these complexities. In view of the unclear transmission mechanism of the exciting force in the variable cycle engine structure, the limited coverage of measurement points and the number of data samples in the load test, and the difficulty in describing the load environment, it is necessary to establish a variable cycle whole machine dynamics analysis method to analyze the impact of different excitations on the dynamic characteristics of the whole machine.

[0003] At present, most dynamic analysis methods are mainly focused on traditional aircraft engines. There are relatively few studies on variable cycle engines, and they lack systematicity and precision. In addition, the existing numerical simulation tools and experimental verification methods are difficult to cope with the complexity of the variable cycle engine overall model, resulting in the accuracy and reliability of the analysis results being limited.

[0004] To this end, we propose a variable cycle engine whole machine dynamics analysis method based on the finite element method. Summary of the invention

[0005] The present invention mainly solves the technical problems existing in the above-mentioned prior art and provides a variable cycle engine whole machine dynamics analysis method based on the finite element method.

[0006] In order to achieve the above object, the present invention adopts the following technical solution, a variable cycle engine whole machine dynamics analysis method based on finite element method, specifically comprising the following steps:

[0007] Step 1: Establish a high-precision variable cycle whole machine finite element model: Use the step-by-step modeling idea to establish a high-precision whole machine finite element model;

[0008] Step 2: Calculation of whole machine response: Input the mathematical representation model of the excitation received by the engine into the whole machine finite element model, use finite element simulation software to perform harmonic response analysis on the whole machine model, and extract the surface response data of the casing;

[0009] Step 3: Use sensitivity analysis method for dynamic analysis: Use MATLAB software to write a program to perform sensitivity analysis on the response calculation results, study the impact of different rotor excitations on the engine surface, and predict and optimize the engine's performance and reliability.

[0010] Preferably, the specific steps of the first step are: the variable cycle engine whole machine modeling adopts the hierarchical modeling concept to perform dynamic modeling and model confirmation of the whole machine rotor system, the first layer, single component modeling and confirmation; the second layer, component connection structure modeling and confirmation; the third layer, whole machine model modeling and confirmation, firstly, the single casing component is dynamically modeled and model confirmed, then the casing assembly and rotor assembly containing the bolt connection structure are dynamically modeled and model confirmed, and finally, the whole machine rotor-support-casing-installation node system is dynamically modeled and model confirmed.

[0011] Preferably, the specific steps of the second step are: calculating the vibration response by finite element software, and the motion differential equation of the entire rotor system of the aircraft engine can be expressed as follows:

[0012] Mu(ω)+(C+G)u(ω)+Ku(ω)=f(ω)

[0013] Among them, M, C, G, K represent the mass, damping, gyroscopic torque, and stiffness matrix of the whole rotor system respectively; u(ω) is the displacement discrete vector of the nodes of the whole rotor system that changes with the excitation frequency; f(ω) is the system load excitation matrix; ω is the system excitation frequency, and the expression of the system displacement response can be further expressed as:

[0014] u(ω)=[K-ω 2 M+iω(C+G)] -1 f(ω)

[0015] f(ω) can be expressed in vector form:

[0016] f(ω)=[f1(ω),f2(ω),...,f k (ω),...,f n (ω)] T

[0017] Among them, f k (ω) represents the excitation of the system in the direction of the kth degree of freedom, n represents the total number of degrees of freedom of the system, and f k (ω) is related to the system load amplitude and excitation frequency and can be expressed by the following formula:

[0018]

[0019] Among them, a k is the load amplitude.

[0020] Preferably, the specific steps of the third step are: for the sensitivity analysis of the vibration response, the influence of the load on the surface of the engine casing can be analyzed. Therefore, in order to analyze the influence of different loads on the dynamics of the whole system, it is necessary to perform sensitivity analysis on the response calculation results. Common sensitivity analysis methods mainly include the derivation method and the finite difference method. The derivation method requires the derivation of both sides of the motion differential equation of the whole system with respect to the rotor excitation:

[0021]

[0022] in,

[0023]

[0024] The sensitivity of displacement response to excitation amplitude can be expressed as:

[0025]

[0026] Derivative of the excitation load with respect to the load amplitude for So the sensitivity of the response to the excitation amplitude can be expressed as:

[0027]

[0028] The present invention provides a variable cycle engine whole machine dynamics analysis method based on the finite element method.

[0029] It has the following beneficial effects:

[0030] 1. This variable cycle engine whole machine dynamics analysis method based on the finite element method establishes a high-precision finite element model of the aircraft engine whole machine through the strategy of distributed model correction, so that it can reflect the actual engine working conditions, and then by inputting the mathematical characterization model of the engine excitation into the established high-precision finite element model, it can effectively predict the response of the engine under the working environment, predict and optimize the performance and reliability of the engine, and save the manpower and test equipment resource costs of the variable cycle engine whole machine test.

[0031] 2. This is a variable cycle engine whole machine dynamics analysis method based on the finite element method. This method combines modern numerical simulation technology and vibration analysis theory. By establishing an accurate variable cycle engine model, it simulates the input load of the engine working environment on the basis of the established high-precision model, predicts and optimizes the engine's performance and reliability, and is of great significance to engine fault diagnosis, health monitoring and parameter identification.

[0032] 3. This variable cycle engine whole machine dynamics analysis method based on the finite element method can not only adapt to the complexity of the variable cycle engine, but also can be applied to the rotor dynamics analysis of active aircraft engines and large gas turbines, etc., and has wide applicability and practical application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 The figure is a flow chart of the method of the present invention. DETAILED DESCRIPTION

[0034] In order to more clearly illustrate the implementation methods of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for the implementation methods or the description of the prior art. Obviously, the drawings described below are only exemplary, and for ordinary technicians in this field, other implementation drawings can be derived from the provided drawings without creative work.

[0035] The structures, proportions, sizes, etc. illustrated in this specification are only used to match the contents disclosed in the specification so as to facilitate understanding and reading by persons familiar with the technology. They are not used to limit the conditions under which the present invention can be implemented, and therefore have no substantial technical significance. Any structural modification, change in proportion or adjustment of size shall still fall within the scope of the technical contents disclosed in the present invention without affecting the effects and purposes that can be achieved by the present invention.

[0036] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0037] In the description of the embodiments of the present invention, it should be noted that the terms "center", "upper", "lower", "inner", "outer", "side", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship in which the invented product is usually placed when in use, which is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", etc. are only used to distinguish the description, and cannot be understood as indicating or implying relative importance.

[0038] In the description of the embodiments of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the embodiments of the present invention can be understood according to specific circumstances.

[0039] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0040] Embodiment 1: A method for dynamic analysis of a variable cycle engine based on finite element method, such as Figure 1 As shown, it specifically includes the following steps: the first step: establish a high-precision variable cycle whole machine finite element model: adopt the step-by-step modeling idea to establish a high-precision whole machine finite element model; the second step: whole machine response calculation: input the mathematical representation model of the excitation received by the engine into the whole machine finite element model, use the finite element simulation software to perform harmonic response analysis on the whole machine model, and extract the casing surface response data; the third step: use the sensitivity analysis method to perform dynamic analysis: use matlab software to write a program, perform sensitivity analysis on the response calculation results, study the influence of different rotor excitations on the engine surface, and predict and optimize the performance and reliability of the engine. The specific steps of the first step are: the variable cycle engine whole machine modeling adopts the hierarchical modeling idea to perform the dynamic modeling and model confirmation of the whole machine rotor system. The first layer is the modeling and confirmation of the single component; the second layer is the modeling and confirmation of the component connection structure; the third layer is the modeling and confirmation of the whole machine model. First, the dynamic modeling and model confirmation of the single component of the casing, then the dynamic modeling and model confirmation of the casing assembly and rotor assembly containing the bolt connection structure, and finally the dynamic modeling and model confirmation of the whole machine rotor-support-casing-installation node system. The specific steps of the second step are: calculate the vibration response through finite element software, and the motion differential equation of the entire rotor system of the aircraft engine can be expressed as follows: Mu(ω)+(C+G)u(ω)+Ku(ω)=f(ω)

[0041] Among them, M, C, G, K represent the mass, damping, gyroscopic torque, and stiffness matrix of the whole rotor system respectively; u(ω) is the displacement discrete vector of the nodes of the whole rotor system that changes with the excitation frequency; f(ω) is the system load excitation matrix; ω is the system excitation frequency, and the expression of the system displacement response can be further expressed as: u(ω)=[K-ω 2 M+iω(C+G)] -1 f(ω)

[0042] f(ω) can be expressed in the form of a vector: f(ω)=[f1(ω),f2(ω),...,f k (ω),...,f n (ω)] T

[0043] Among them, f k (ω) represents the excitation of the system in the direction of the kth degree of freedom, n represents the total number of degrees of freedom of the system, and f k (ω) is related to the system load amplitude and excitation frequency and can be expressed by the following formula:

[0044] Among them, a k is the load amplitude. The specific steps of the third step are: for the sensitivity analysis of the vibration response, the influence of the load on the surface of the engine casing can be analyzed. Therefore, in order to analyze the influence of different loads on the dynamics of the whole system, it is necessary to perform sensitivity analysis on the response calculation results. Common sensitivity analysis methods mainly include the derivative method and the finite difference method. The derivative method requires the derivative of both sides of the motion differential equation of the whole system with respect to the rotor excitation:

[0045] in,

[0046] The sensitivity of displacement response to excitation amplitude can be expressed as:

[0047] Derivative of the excitation load with respect to the load amplitude for So the sensitivity of the response to the excitation amplitude can be expressed as:

[0048] A high-precision finite element model of the entire aircraft engine is established through the strategy of distributed model correction, so that it can reflect the actual engine working conditions. Then, by inputting the mathematical characterization model of the engine excitation into the established high-precision finite element model, the response of the engine under the working environment can be effectively predicted, and the performance and reliability of the engine can be predicted and optimized, saving manpower and test equipment resource costs for variable cycle engine testing.

[0049] Embodiment 2: Based on Embodiment 1, Figure 1 As shown, the specific steps are:

[0050] Step 1: Establish a high-precision variable cycle complete machine finite element model;

[0051] Step 2: Calculation of whole machine response: For the whole machine finite element model, apply unbalanced excitation on the engine low-pressure rotor fan disk, divide the unbalanced excitation into two directions, x and y, and apply it to the disk center. Apply the rotation speed on the rotor components, and generate periodic excitation by the unbalanced quantity. Calculate the displacement response of the whole machine under the unbalanced excitation by using harmonic response analysis. In order to reflect multiple speed conditions of the whole machine, the speed calculation under multiple conditions near the critical speed and adjacent speed of the whole machine can be performed.

[0052] Step 3: Based on the results of the whole machine response analysis in the previous step, a sensitivity analysis method is used for dynamic analysis: Based on the response analysis of the whole machine rotor system, according to the sensitivity analysis method of the response of any point on the whole machine casing surface to the rotor load excitation, the sensitivity of the vibration response to the rotor imbalance is calculated. Through calculation, the sensitivity of the casing surface response to the rotor imbalance at different speeds can be obtained, and it can be found that the imbalance has the greatest impact on the vibration of the whole machine. Finally, in order to obtain the total impact of the rotor imbalance on the whole machine, the average sensitivity of the casing surface at multiple speeds is calculated, and the calculation formula is as follows:

[0053]

[0054] The influence of the low-pressure fan imbalance on the whole machine dynamics is thus obtained, verifying the effectiveness of the variable cycle engine whole machine dynamics analysis of the present invention. This method combines modern numerical simulation technology and vibration analysis theory, establishes an accurate variable cycle engine model, simulates the input load of the engine working environment on the basis of the established high-precision model, predicts and optimizes the performance and reliability of the engine, and has great significance for engine fault diagnosis, health monitoring and parameter identification.

[0055] Embodiment 3: Based on Embodiment 1 and Embodiment 2, Figure 1 As shown in the figure, the specific process of establishing a high-precision variable cycle whole machine finite element model is as follows:

[0056] S1: Modeling and confirmation of single components: First, a hypermodel of a single component is established. The hypermodel is a highly refined three-dimensional solid finite element model that is consistent with the actual geometric model and has a large enough mesh density to accurately reflect the dynamic characteristics of the structure. Then, the geometric model of the single component is simplified by removing geometric features that have little effect on the dynamics, such as bolt holes and chamfers on the side. A second-order hexahedral mesh is used for the rear bearing casing after the geometric structure is simplified. Finally, the virtual modal parameters of the hypermodel are used to modify the simplified model to obtain a simplified model with both high accuracy and high efficiency.

[0057] S2: Modeling and confirmation of component connection structure: Thin layer entity elements are used to make the bolt connection structure equivalent. First, the super model is spliced ​​using thin layer entity elements to construct the super model connection structure. Then, the simplified model of the connection model is constructed using the equivalent thin layer. Finally, the simplified model of the connection structure is corrected using the connected super model, so that the simplified connection model has higher accuracy and calculation efficiency.

[0058] S3: Whole machine modeling and confirmation: For the confirmed engine rotor finite element model and stator case finite element model, the engine bearing structure is simulated using spring units, and the case and rotor are connected with spring units to finally obtain a multi-duct case-rotor system finite element model.

[0059] The present invention can not only adapt to the complexity of variable cycle engines, but also be applied to rotor dynamics analysis of current aircraft engines and large gas turbines, and has wide applicability and practical application value.

[0060] Working principle of the present invention: This method can accurately simulate the dynamic response of the engine under various working conditions by establishing a high-precision variable cycle whole machine finite element model. Through harmonic response analysis, the vibration response data of the casing surface can be extracted, which is crucial for understanding the dynamic behavior of the engine in actual operation. In addition, through sensitivity analysis, the impact of different rotor excitations on engine performance can be evaluated, thereby providing a scientific basis for engine design and optimization. This method not only improves the accuracy of the analysis, but also reduces R&D costs and shortens the R&D cycle by reducing reliance on physical experiments. Ultimately, this method can provide strong technical support for reliability assessment and performance optimization of variable cycle engines, and has important engineering application value.

[0061] The above shows and describes the basic principles and main features of the present invention and the advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A variable cycle engine whole machine dynamics analysis method based on finite element method, characterized in that: The specific steps include: Step 1: Establish a high-precision variable cycle whole machine finite element model: Use the step-by-step modeling idea to establish a high-precision whole machine finite element model; Step 2: Calculation of whole machine response: Input the mathematical representation model of the excitation received by the engine into the whole machine finite element model, use finite element simulation software to perform harmonic response analysis on the whole machine model, and extract the surface response data of the casing; Step 3: Use sensitivity analysis method for dynamic analysis: Use MATLAB software to write a program to perform sensitivity analysis on the response calculation results, study the impact of different rotor excitations on the engine surface, and predict and optimize the engine's performance and reliability.

2. The variable cycle engine whole machine dynamics analysis method based on finite element method according to claim 1 is characterized by: The specific steps of the first step are: the variable cycle engine whole machine modeling adopts the hierarchical modeling concept to carry out the dynamic modeling and model confirmation of the whole machine rotor system, the first layer, the single component modeling and confirmation; the second layer, the component connection structure modeling and confirmation; the third layer, the whole machine model modeling and confirmation, firstly, the single casing component is dynamically modeled and the model is confirmed, then the casing assembly and rotor assembly including the bolt connection structure are dynamically modeled and the model is confirmed, and finally the whole machine rotor-support-casing-installation node system is dynamically modeled and the model is confirmed.

3. The variable cycle engine whole machine dynamics analysis method based on finite element method according to claim 1 is characterized in that: The specific steps of the second step are: calculate the vibration response by finite element software, and the motion differential equation of the entire rotor system of the aircraft engine can be expressed as follows: Mu(ω)+(C+G)u(ω)+Ku(ω)=f(ω) Among them, M, C, G, and K represent the mass, damping, gyroscopic moment, and stiffness matrix of the whole rotor system respectively; u ( ω ) is the discrete displacement vector of the nodes of the whole rotor system that changes with the excitation frequency; f ( ω ) is the system load excitation matrix; ω is the system excitation frequency, which can be further expressed as the system displacement response: u(ω)=[K-ω 2 M+iω(C+G)] -1 f(ω) f(ω) can be expressed in vector form: f(ω)=[f1(ω),f2(ω),...,f k (ω),...,f n (oh)] T Among them, f k (ω) represents the excitation of the system in the direction of the kth degree of freedom, n represents the total number of degrees of freedom of the system, and f k (ω) is related to the system load amplitude and excitation frequency and can be expressed by the following formula: Among them, a k is the load amplitude.

4. The variable cycle engine whole machine dynamics analysis method based on finite element method according to claim 1 is characterized in that: The specific steps of the third step are: for the sensitivity analysis of the vibration response, the influence of the load on the surface of the engine casing can be analyzed. Therefore, in order to analyze the influence of different loads on the dynamics of the whole system, it is necessary to perform sensitivity analysis on the response calculation results. Common sensitivity analysis methods mainly include the derivation method and the finite difference method. The derivation method requires the derivation of both sides of the motion differential equation of the whole system with respect to the rotor excitation: in, The sensitivity of displacement response to excitation amplitude can be expressed as: Derivative of the excitation load with respect to the load amplitude for So the sensitivity of the response to the excitation amplitude can be expressed as:

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