Rapid Analysis Method for Mechanical Properties of Aero-engine Rotor-Elastic Annular Oil Film

Abstract

This invention belongs to the field of aero-engine vibration control and rotor dynamics simulation technology, specifically involving a rapid analysis method for the mechanical properties of the rotor-elastic ring oil film in aero-engines. It establishes the rotor-elastic ring coupled dynamic equations; by discretizing the elastic ring using shell elements, deformation features are extracted in polar coordinates; and the inner and outer oil films are modeled in the fluid domain using the Reynolds equation and the orifice throttling equation, thus accurately characterizing the nonlinear dynamics of the oil film under multi-protrusion and porous structures. Based on modal mapping, the normal velocity of the elastic ring wall is projected onto the oil film equation to iteratively solve for the oil film pressure. The pressure is then reflected back to the rotor-elastic ring coupled system to update its displacement field until convergence. This invention efficiently screens and optimizes structural parameters such as the number of protrusions, oil film thickness, and orifice size over a wide speed range, thereby improving the vibration reduction performance and design efficiency of the aero-engine rotor support system.

Description

Technical Field

[0001] This invention belongs to the field of aero-engine vibration control and rotor dynamics simulation technology, specifically relating to a rapid analysis method for the mechanical properties of aero-engine rotor-elastic ring oil film. Background Art

[0002] As aero-engines continue to evolve towards higher thrust-to-weight ratios and higher reliability, their internal rotor system designs are trending towards high speed, lightweight construction, and multi-stage coupling. To meet the need for suppressing rotor vibration at high speeds, various damping support schemes have emerged. Among them, structures represented by squeeze film dampers (SDF) and elastic ring squeeze film dampers (ERSFD) have received widespread attention in modern aero-engines. The elastic ring structure can provide a certain degree of stiffness and damping between the rotor and the casing. By separating the oil film chambers through perforations or bosses on the ring wall, it achieves throttling and energy dissipation of the oil film flow. However, the oil film nonlinearity, elastic ring shell deflection, bending deformation of the high-speed flexible rotor, and gyroscopic effects introduced by this type of support make the rotor-oil film-elastic ring coupling analysis particularly complex.

[0003] Most existing studies, when calculating the rotor-oil film mechanical properties, such as some literature (CN113656917B, a fluid-structure interaction calculation method for an elastic ring-type extrusion oil film damper), often employ the following two types of methods: One type is transient coupled numerical simulation based on the Navier-Stokes equations or a full-field hydrodynamic model. This method captures oil film pressure and elastic ring deformation by refining the time-domain stepping. Although it can theoretically reflect the fluid-structure interaction process relatively completely, the computational scale is enormous and the time cost of a single parameter analysis is extremely high when the rotor is high-speed and structurally complex, making it difficult to meet the needs of multi-parameter and fast iteration in the design stage. The other type simplifies the model by only considering the unbalanced excitation caused by rotor eccentricity or simple film damping, ignoring the influence of elastic ring wall deflection and orifice throttling on oil film distribution. Therefore, it has deviations in predicting vibration characteristics and nonlinear effects in the high-speed range. Especially when the rotor spans multiple critical speeds and the elastic ring has multiple bosses and small holes, it is difficult to accurately evaluate the frequency dependence characteristics of oil film stiffness and damping using simplified methods, and it is also impossible to take into account the rapid screening of different geometric parameters (such as the number of bosses, the size of the holes, the thickness of the oil film, etc.).

[0004] To address the aforementioned shortcomings, an analytical method is needed that can consider the flexural deformation and gyroscopic effects of high-speed flexible rotors, effectively describe the multi-chamber oil film flow and orifice throttling effects of the elastic ring, and possess high computational efficiency. Only by reducing the high cost of transient coupling and shortening the computation cycle while accurately capturing key fluid-structure interaction mechanisms (including multi-orifice oil film flow, elastic ring deformation, and angular deformation) can we better serve the design and optimization of aero-engine rotor support systems. Based on this, this invention proposes a numerical analysis method that can quickly and reliably predict the dynamic characteristics of the oil film by establishing rotor-elastic ring coupling equations in modal coordinates and combining oil film pressure distribution iteration with orifice throttling equations. This method can evaluate multiple sets of structural parameters in a shorter computation time, solving the problem of existing algorithms struggling to balance computational cost and accuracy. Summary of the Invention

[0005] This invention addresses the need for dynamic characteristic analysis of elastic ring-oil film damping structures in aero-engine rotor support systems. It proposes a rapid analysis method for the mechanical properties of the rotor-elastic ring oil film in aero-engines. This method can simultaneously consider the flexural deformation of high-speed flexible rotors and the throttling effect of porous channels (or small holes) in the elastic ring. By establishing coupled dynamic equations of rotor-elastic ring-oil film in modal coordinates and combining iterative algorithms, the dynamic characteristics of the oil film under different structural parameters can be quickly obtained. This provides a fast, efficient, and accurate theoretical and numerical analysis method for the optimized design of engine rotor vibration reduction structures.

[0006] This invention is implemented by providing a rapid analysis method for the mechanical properties of an aero-engine rotor-elastic ring oil film, comprising the following steps:

[0007] S1: Establish the rotor-elastic ring coupled dynamic equations for a high-speed flexible rotor. First, taking the supported aero-engine rotor as the research object, the generalized coordinate equations of the rotor are obtained based on the second kind of Lagrange equations, denoted as:

[0008]

[0009] in, The kinetic energy of the rotor, The potential energy of the rotor. This represents the damping dissipation energy of the system. For generalized coordinate components, for high-speed flexible rotors, it is necessary to explicitly consider the rotor's flexural deformation and its influence on the displacement and angle at the supports, and obtain the rotor mass matrix through finite element discretization using solid elements, shell elements, and beam elements. Stiffness matrix gyroscope matrix With damping matrix ;

[0010] For the elastic ring, a finite element model is established using the thin-walled shell element theory to obtain the stiffness matrix of the elastic ring. quality matrix and damping matrix Subsequently, the rotor and the elastic ring are combined to form the rotor-elastic ring coupled dynamic equation, denoted as:

[0011]

[0012] in, and Let F be the acceleration and velocity under the generalized coordinate q, respectively. F includes the oil film force and the unbalanced force. If we only care about the intrinsic influence of the oil film force, we can temporarily ignore the unbalanced excitation in order to simplify the study of the mechanical properties of the elastic ring oil film.

[0013] S2: Establish the solution equation for the oil film pressure field. An inner oil film and an outer oil film are formed between the elastic ring and the rotor, and between the outer side of the elastic ring and the bearing housing, respectively. Several through holes are arranged on the elastic ring to allow oil to flow between the chambers. Using the Reynolds equation, the pressure distribution of the inner and outer oil films can be written as follows:

[0014] ;

[0015]

[0016] in, Indicates the thickness of the oil film. For oil film pressure, The viscosity coefficient is given by the subscripts in and ot, which represent the inner and outer oil films, respectively. , , These are angular coordinates, axial coordinates, and time, respectively. For rotational speed, Where is the radius of the elastic ring. For the radial deflection deformation of the elastic ring, the orifice throttling effect is addressed by introducing the orifice throttling equation (Hagen-Poiseuille equation) to describe the relationship between flow rate and pressure difference at the orifice:

[0017]

[0018] in, For traffic, The orifice diameter, The length of the damping orifice. Given the pressure difference at both ends of the orifice, the orifice flow conservation equation and the oil film pressure in the adjacent chambers are solved iteratively to obtain the pressure field distribution of the inner and outer oil films and the orifice flow distribution.

[0019] S3: Modal vector extraction and oil film dynamic characteristic analysis. When considering the vibration reduction characteristics of the elastic ring support-rotor system near a certain critical speed, the unbalanced load can be ignored first. Natural modal analysis of the rotor-elastic ring coupled system yields the following characteristic equations:

[0020]

[0021] The characteristic frequency can be obtained by solving this equation. and mode vectors That is, the modal deformation is obtained, and the projection of the modal deformation is the normal velocity excitation of the elastic ring wall surface;

[0022] S4: In subsequent oil film pressure calculations, this modal deformation is projected as a "wall velocity excitation" and coupled with the oil film equation to solve for the pressure distribution. The oil film force after pressure integration can be mapped back to the modal coordinate system, thus obtaining the oil film stiffness and damping under this mode, denoted as...

[0023] ;

[0024]

[0025] in, , These are the amplitudes of modal displacement and velocity, respectively. As the projection of oil film force in modal coordinates, this analysis method incorporates rotor angular deflection and orifice throttling effect into the iterative process, effectively improving the accuracy of the results and being more efficient than traditional transient coupled simulation.

[0026] The iterative and fast convergence strategy, during coupled calculation, requires each iteration to correct the oil film thickness based on the new deformation of the elastic ring, and then solve the pressure distribution using the oil film equation and the orifice flow equation, while simultaneously updating the oil film force and mapping it back to the elastic ring model; if the maximum change in the oil film force coefficient or pressure distribution between two adjacent iterations is lower than a preset threshold, convergence is considered achieved; since the elastic ring and rotor are only at half a circumference ( The contact area of ​​the boss bears the main radial force, so this half-circumference area can be divided into a separate contact surface, while the other half-circumference is regarded as a free boundary, which is closer to the actual working situation. Unlike the traditional transient iteration, this method simplifies the application of normal motion by using modal vectors, which greatly reduces the amount of calculation and makes it possible to quickly adjust the structural parameters such as different through hole layouts, hole diameters, number of bosses, and material stiffness.

[0027] Compared with the prior art, the advantages of the present invention are:

[0028] (1) The “rapid analysis method for mechanical properties of oil film in rotor-elastic ring” proposed in this invention greatly improves the analysis efficiency while ensuring the accuracy of the model, and can efficiently evaluate the mechanical properties of oil film in elastic ring support in the multi-stage critical speed region.

[0029] (2) This method fully considers the flexural deformation of the high-speed flexible rotor and the throttling effect of the orifice. Compared with the traditional model that ignores the rotor angular deformation or lacks orifice flow calculation, it is closer to the actual working conditions and is conducive to parameter optimization and structural design.

[0030] (3) The generalized coupling modeling approach of this method for elastic ring shells and oil film flow can be further extended to other viscous damping support structures with thin-walled porous features, providing an efficient and practical technical means for vibration control and reliability research of modern aero engines and other high-end rotor equipment. Attached Figure Description

[0031] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1 This is a schematic diagram illustrating the structural features of an aero-engine elastic ring support-rotor system in one embodiment.

[0033] Figure 2 A schematic diagram of an elastic ring support structure in one embodiment;

[0034] Figure 3 This invention presents a rapid analysis method for the mechanical properties of the rotor-elastic ring oil film in aero-engines.

[0035] Figure 4 This is a schematic diagram showing the results of modal feature vector calculations performed for the specific embodiment.

[0036] Figure 5 This is a schematic diagram of the rapid analysis results of the mechanical properties of the elastic annular oil film with different parameters carried out for the embodiment, where the damping coefficient is (a) and the stiffness coefficient is (b). Detailed Implementation

[0037] To more clearly illustrate the technical solutions of the specific embodiments of the present invention, the present invention will be further described below in conjunction with the accompanying drawings and examples. It is obvious that the described embodiments are one possible parameter setting of the present invention, and all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] To further verify and illustrate the rapid analysis method for the mechanical properties of the rotor-elastic ring oil film in aero-engines, a representative example of an elastic ring-supported rotor system model is used to conduct dynamic numerical solutions and result comparison analysis. The structural schematic of this elastic ring-supported rotor system is shown below. Figure 1 As shown, the structure includes a first bearing 1, a second bearing 2, a third bearing 4, a fourth bearing 5, a shaft 3, and a turbine assembly 6. An elastic ring is arranged on the third bearing 4 and the fourth bearing 5. The rotor length is 130 mm, the turbine assembly mass is 63 kg, and the material's elastic modulus is 195 GPa. The elastic ring structure is as follows: Figure 2 As shown, 7 is the elastic ring boss, and 8 is the damping hole. Under the designed working condition, the gap between the elastic ring and the mating surface is filled with lubricating oil. This allows the lubricating oil to flow through the damping hole during the deformation of the elastic ring by the rotor, generating flow damping, suppressing and dissipating vibration energy. Structurally, the elastic ring has an axial length of 21 mm, a material elastic modulus of 205 GPa, a ring wall thickness of 1 mm, a damping hole diameter of 0.8 mm, a ring diameter of 80 mm, a boss height of 0.2 mm, and 8 bosses.

[0039] The process method in this embodiment is as follows: Figure 3 As shown, the specific steps are as follows:

[0040] S1: Establish the rotor-elastic ring coupled dynamic equations, such as Figure 1 In this embodiment, the overall structural features of the engine power turbine rotor are first addressed by simplifying the rotor's three-dimensional geometry in CAD software. Small chamfers and non-critical bosses are removed, leaving only the main shaft and disc structure, which play a decisive role in the overall bending stiffness and mass distribution. Subsequently, finite element software (such as ANSYS, ABAQUS, or NASTRAN) is used to discretize the rotor into solid elements, beam elements, and shell elements, respectively, and the rotor's mass matrix is ​​obtained. Stiffness matrix gyroscope matrix With internal damping matrix This allows for the accurate representation of flexible bending and gyroscopic effects under high-speed rotation in subsequent analyses.

[0041] Meanwhile, the elastic ring is modeled using thin-walled shell elements. Specifically, the process involves first establishing a finite element model of the elastic ring based on its geometric definition, thereby obtaining the stiffness matrix of the overall elastic ring. With the mass matrix This shell element model can fully consider the bending deformation of the ring in the radial and circumferential directions, as well as the thin-wall deflection in the axial direction. After the elastic ring is discretized by finite element method, it can be updated and reconstructed multiple times based on parameters such as ring radius, thickness, axial length, boss height, number of bosses, and orifice size to meet the needs of subsequent parametric analysis. Finally, the rotor and elastic ring are rigidly coupled in the support area, and the outer wall nodes of the elastic ring are docked with the casing or shell constraint elements to assemble the system into coupled dynamic equations:

[0042]

[0043] In the "oil film mechanical property analysis" stage that this embodiment focuses on, rotor unbalance force is not considered in F for the time being, so as to focus on the intrinsic influence of the elastic ring-oil film on vibration characteristics; if it is necessary to evaluate the actual operating conditions later, the unbalance force term can also be incorporated into the equation for comprehensive calculation.

[0044] S2: Establish the solution equation for the oil film pressure field. In this embodiment, the gap between the inner wall of the elastic ring and the outer surface of the rotor is defined as the inner oil film region, and the gap between the outer wall of the elastic ring and the casing or bearing housing is defined as the outer oil film region. Several oil film chambers are formed by encapsulating the end face seal or boss area. According to the Reynolds equation for the inner oil film:

[0045]

[0046] Reynolds equation for external oil film:

[0047]

[0048] If the elastic ring has multiple bosses, the chamber is correspondingly divided into multiple circumferential segments; the orifices arranged on the elastic ring serve as channels between adjacent chambers, according to the Hagen-Poiseuille equation:

[0049]

[0050] To depict the diameter of the orifice and pressure difference With traffic The relationship is established, and a flow conservation condition is set at each orifice to connect the oil film pressure in the chamber. In this way, the fluid domain equations of the inner and outer oil films and the orifices can be obtained at the discrete level, laying the foundation for subsequent iterative solution of oil film force.

[0051] S3: Modal vector extraction and oil film dynamic characteristic analysis, yielding results similar to... Figure 4The rotor-support configuration is shown, where 9 represents the rotor's characteristic vector mode shape and 10 represents the elastic ring's characteristic vector mode shape. In this embodiment, to quickly obtain the damping and stiffness characteristics of the elastic ring-oil film on rotor vibration at different speeds, a modal vector projection method is used: first, modal analysis is performed on the aforementioned coupled system at given speeds (such as multiple operating points like 3000, 6000, 9000...18000 rev / min, etc.) to solve for the following:

[0052]

[0053] Obtain the characteristic frequency of the gyroscope coupled under this rotational speed condition. and modal deformation Next, the normal velocity of the elastic ring wall in this mode is mapped to the oil film domain as the "velocity excitation" of the Reynolds equation;

[0054] S4: Solve for the oil film pressure based on S3. This pressure is integrated at the shell element node as an oil film force. This feedback is then sent to the elastic ring to update its deformation field and correct the oil film thickness. The process is repeated; when the change in peak oil film force or pressure in adjacent iterations falls below a certain set threshold (e.g., 1%), the oil film pressure field is considered to have converged. After convergence, the final oil film force components can be decomposed into equivalent stiffness and damping, i.e.:

[0055] ;

[0056]

[0057] This implementation method follows an iterative and convergence strategy when analyzing various parameters such as the number of bosses, oil film thickness, and orifice diameter: First, a set of parameters is fixed (e.g., 8 bosses, 0.8mm orifice diameter), and the process of "modal analysis → oil film pressure solution → elastic ring deformation update → convergence judgment" is completed at each target speed. Then, the target parameters are changed and the process is repeated to obtain a series of damping / stiffness curves showing the variation of parameters and speed. This method simplifies the wall excitation form by using modal vectors, significantly reducing the high computational cost of traditional transient coupling's step-by-step iteration in the time domain, thus enabling multi-parameter scanning over a wide speed range in a shorter time. When more detailed results are needed, sampling points can be densified near the target parameters (e.g., the number of bosses can be increased from 6, 8, 10, 12 to 14, or the orifice diameter can be increased from 0.2mm to 2.0mm in several steps) and the same process can be repeated to obtain more accurate oil film dynamic curves, such as... Figure 5(a) and (b). By comprehensively comparing these curves, the optimal design range for the number of bosses, oil film thickness, or orifice size can be found. For example, at what speed, which orifice diameter can be selected to balance sufficient damping and controllable stiffness, thereby improving the stability and vibration reduction performance of the aero-engine power turbine rotor system. In summary, this embodiment meticulously demonstrates the calculation process of elastic ring shell element modeling and oil film fluid iterative coupling, and achieves accurate and effective analysis of multiple parameters through modal projection and fast convergence strategies, providing a practical and feasible method for vibration control and structural optimization design of aero-engine rotor supports.

[0058] The specific embodiments described above are merely preferred embodiments of the present invention. It should be understood that the scope of protection of the present invention is not limited to the specific embodiments. Without departing from the principles of the present invention, any modifications, alterations, substitutions, or replacements of the simulation object made by those skilled in the art to the technical solutions of the present invention, or any changes to the simulation object, should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A rapid analysis method for the mechanical properties of an aero-engine rotor-elastic annular oil film, characterized in that, Includes the following steps: S1: Establish a finite element dynamic model of a high-speed flexible rotor, simplify the rotor geometrically and discretize it into solid elements, beam elements and shell elements, and obtain the rotor's mass matrix, stiffness matrix, gyroscope matrix and damping matrix; The elastic ring is discretized using thin-walled shell elements to obtain the mass matrix, stiffness matrix, and damping matrix of the elastic ring. The elastic ring is then rigidly or elastically coupled to the rotor support to form a rotor-elastic ring coupled system. The rotor-elastic ring coupled dynamic equation is then assembled using the mass matrix, stiffness matrix, gyroscope matrix, and damping matrix of the rotor, as well as the mass matrix, stiffness matrix, and damping matrix of the elastic ring. S2: Establish the solution equation for the oil film pressure field. An inner oil film and an outer oil film are formed between the elastic ring and the rotor, and between the outer side of the elastic ring and the bearing housing, respectively. Several through holes are arranged on the elastic ring to allow oil to flow between the chambers. Using the Reynolds equation, the pressure distribution of the inner and outer oil films can be written as follows: ； ； in, Indicates the thickness of the oil film. For oil film pressure, The viscosity coefficient is given by the subscripts in and ot, which represent the inner and outer oil films, respectively. , , These are angular coordinates, axial coordinates, and time, respectively. For rotational speed, Where is the radius of the elastic ring. For the radial deflection deformation of the elastic ring, and considering the throttling effect of the through-hole, an orifice throttling equation is introduced to describe the relationship between the flow rate and pressure difference at the orifice: ； in, For traffic, The orifice diameter, The length of the damping orifice. Given the pressure difference at both ends of the orifice, the orifice flow conservation equation and the oil film pressure in the adjacent chambers are solved iteratively to obtain the pressure field distribution of the inner and outer oil films and the orifice flow distribution. S3: Select the inherent mode of the rotor-elastic ring coupling system, deform the inherent mode, and generate normal velocity excitation on the elastic ring wall; S4: By iteratively coupling the solution of oil film pressure distribution and elastic ring displacement correction until the oil film mechanical properties converge, the converged oil film mechanical properties are mapped back to the intrinsic modal coordinate system to obtain the oil film damping and stiffness coefficients under specified speed and structural parameters, thereby realizing the rapid analysis of rotor-elastic ring oil film mechanical properties.

2. The rapid analysis method for the mechanical properties of the aero-engine rotor-elastic ring oil film according to claim 1, characterized in that, In S1, the elastic ring is discretized using four-node or eight-node thin-walled shell elements.

3. The rapid analysis method for the mechanical properties of the aero-engine rotor-elastic ring oil film according to claim 1, characterized in that, In step S4, the normal velocity excitation of the elastic ring wall obtained in step S3 is projected onto the solution equations of the inner and outer oil film pressure fields for iteration.

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