A method for strength check of fan or compressor disc drum connecting bolt

Abstract

This application provides a method for strength verification of fan or compressor disc drum connecting bolts, comprising: determining the loads at the front and rear support points caused by the inertial loads of each stage of the disc drum, the loads at the front and rear support points caused by the centrifugal loads caused by the unbalance of each stage of the disc drum, and the loads at the front and rear support points caused by the gyroscopic torque; obtaining the maximum bending moment of the bolt connection section based on the sum of the three loads; obtaining the maximum tensile stress at the maximum diameter position of the bolt connection section based on the bending normal stress distribution of the circular cross-section beam and the maximum bending moment of the bolt connection section, thereby obtaining the maximum tensile stress load borne by the bolt; determining the temperature load of the connecting bolt and the tensile stress required for the connecting bolt to bear the transmitted torque; obtaining the axial tensile force required for the disc drum connecting bolt to bear during operation based on the sum of the three; and completing the strength verification of the disc drum connecting bolt by ensuring that the axial tensile force meets the allowable requirements and the bolt preload and nut tightening torque requirements.

Description

Technical Field

[0001] This application belongs to the field of aero-engine technology, and specifically relates to a method for strength verification of connecting bolts for fan or compressor disc drums. Background Technology

[0002] To ensure rotor stiffness, current aero-engine fans and compressors all employ a hybrid disc-drum rotor structure, with each stage of the disc-drum connected via short bolts and a locking mechanism. During operation, the short bolt connection, in addition to transmitting torque across each rotor stage, must also ensure a stable connection where the discs at each stage do not become detached. To guarantee the overall rotor stiffness and dynamic stability, and to reduce rotor vibration, the stability of the rotor connections has become a crucial factor to consider in the design of fan or compressor rotor structures.

[0003] Traditional methods for verifying the design of short bolts mainly include empirical formulas and numerical simulation.

[0004] 1) The empirical formula method mainly relies on design experience and general bolt standards, combined with parameters such as bolt connection pitch circle diameter and axial forces at various levels, to design and verify parameters such as the number and diameter of bolts. The empirical formula method has a simple calculation process and high calculation efficiency, but it is difficult to consider issues such as rotor centrifugal speed, bending deformation, and deformation of the mounting edge after bolt tightening that cause bolt connection stability problems in the design verification. For high-speed, long-span compressor fan rotors, the calculation and evaluation error is relatively large.

[0005] 2) Numerical simulation analyzes the stress level at the bolt location by establishing a model of the rotor and bolt connection, thereby evaluating the bolt strength. Numerical simulation has high calculation accuracy, but its evaluation efficiency is low, the solution time is long, and there is a lot of preliminary modeling and simplification work. At the same time, numerical simulation does not consider the influence of rotor bending caused by the imbalance of each stage of disc drum, which will introduce errors in the bolt group strength verification for large-span rotors with multi-stage disc connections. Summary of the Invention

[0006] The purpose of this application is to provide a method for strength verification of connecting bolts for fan or compressor disc drums, in order to solve or mitigate at least one of the problems in the prior art.

[0007] The technical solution of this application is: a method for strength verification of connecting bolts for fan or compressor disc drums, the method comprising:

[0008] Determine the loads at the front and rear support points caused by the inertial loads of each stage of the disc drum acting on the fan or compressor rotor, the loads at the front and rear support points caused by the centrifugal loads caused by the imbalance of each stage of the disc drum, and the loads at the front and rear support points caused by the gyro torque.

[0009] The maximum bending moment of the fan or compressor rotor at a certain bolted connection section is obtained based on the load at the front and rear support positions.

[0010] Based on the bending normal stress distribution of the circular cross-section beam and the maximum bending moment of the bolt connection section, the maximum tensile stress at the position of the maximum diameter of the bolt connection section is obtained. Under the action of this maximum tensile stress, the maximum tensile stress load borne by the bolt is obtained.

[0011] Determine the temperature load generated by the connecting bolts of the fan or compressor rotor under temperature load, and the tensile stress required for the connecting bolts to bear the transmitted torque;

[0012] The axial tensile force required for the disc-drum connection bolt during operation is obtained by summing the maximum tensile stress load, temperature load, and tensile stress required for torsion transmission of the bolt.

[0013] The strength of the disc drum connecting bolts is verified by checking the relationship between the stress borne by the connecting bolts and the allowable requirements, as well as the bolt preload and nut tightening torque, to determine the axial tensile force that the connecting bolts need to bear during operation.

[0014] Furthermore, the loads at the front and rear support points caused by the inertial loads acting on the fan or compressor rotor by each stage of the disc drum are:

[0015]

[0016] In the formula, Q i1 The load at the front support point caused by the inertial loads acting on the fan or compressor rotor by each stage of the disc drum;

[0017] Q i2 The load at the rear support point caused by the inertial loads acting on the fan or compressor rotor by each stage of the disc drum;

[0018] These represent the concentrated mass of each level of rotor disc drum assembly, with subscript N indicating the disc drum number;

[0019] L is the span between the front and rear support points;

[0020] These are the distances from the center of mass of each level of the drum to the front fulcrum;

[0021] K is the rotor overload coefficient;

[0022] g is the acceleration due to gravity.

[0023] Furthermore, the centrifugal load caused by the imbalance of each level of the drum results in loads at the front and rear support points.

[0024]

[0025] In the formula, Qj1 The load at the front support point caused by the centrifugal load resulting from the imbalance of each level of the disc drum;

[0026] Q j2 The load at the rear support point caused by the centrifugal load resulting from the imbalance of each level of the disc drum;

[0027] These are the radii of the centroid of each level of the disc drum;

[0028] n is the fan or compressor speed.

[0029] Furthermore, the loads at the front and rear fulcrum positions caused by the gyroscopic torque are:

[0030]

[0031] In the formula, Q k1 The load at the front pivot point caused by the gyro torque;

[0032] Q k2 The load at the rear pivot point caused by the gyro torque;

[0033] Mt is the gyroscopic torque.

[0034] Furthermore, the loads at the front and rear support points yield the maximum bending moment M of the fan or compressor rotor at a specific bolted connection section. x for: .

[0035] Furthermore, the maximum tensile stress at the location of the maximum diameter of the bolted connection section is:

[0036]

[0037] In the formula, D is the maximum outer diameter of the effective bolt clamping area annulus. , The minimum inner diameter of the annulus within the effective bolt clamping area. , For the bolt installation pitch circle diameter, The nominal diameter of the bolt;

[0038] The maximum tensile stress load that the bolt can withstand under this maximum tensile stress is:

[0039]

[0040] In the formula, Z represents the number of bolts.

[0041] Furthermore, the temperature load generated by the connecting bolts is:

[0042] In the formula, For the thermal deformation of the mounting edge of the disc, For the thermal deformation of the bolt, Let be the static stiffness of the bolt.

[0043] Furthermore, the tensile stress required for the connecting bolts to bear the transmitted torque is:

[0044]

[0045] In the formula, The starting torque required for each stage of the disks before section x;

[0046] denoted as the coefficient of friction of the drum connecting surface.

[0047] Furthermore, the relationship between the stress σ borne by the connecting bolts and the allowable requirement is as follows:

[0048]

[0049] In the formula, This refers to the allowable stress value of the material.

[0050] This is the bolt size factor;

[0051] This refers to the manufacturing process coefficient;

[0052] This is the coefficient for non-uniformity of stress.

[0053] The notch stress concentration factor;

[0054] This is for the safety factor.

[0055] Furthermore, bolt preload satisfy:

[0056] In the formula, This is the residual preload coefficient. This refers to the relative stiffness coefficient of the bolted connection;

[0057] The nut tightening torque M0 satisfies:

[0058] In the formula, H is the tightening torque coefficient, and s is the correction coefficient.

[0059] The strength verification method for fan or compressor rotor disc drum connecting bolts proposed in this application is simple in process and highly efficient in calculation. It fully considers the influence of rotor bending deformation caused by rotor rotation centrifugal force, unbalance, gyro torque, etc. on bolt strength loss. This method can be used to guide the design of bolt specifications, tightening torque, etc. in the design stage of fan or compressor rotor, which can greatly improve design efficiency. Attached Figure Description

[0060] To more clearly illustrate the technical solutions provided in this application, the accompanying drawings will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application.

[0061] Figure 1 This is a flowchart of the strength verification method for the disc-drum connecting bolts in this application.

[0062] Figure 2 This is a schematic diagram of the compressor rotor structure of a six-stage disc drum according to an embodiment of this application.

[0063] Figure 3 This is a diagram showing the distribution of normal stress at each level of the drum in an embodiment of this application. Detailed Implementation

[0064] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application will be described in more detail below with reference to the accompanying drawings.

[0065] This application proposes a new strength verification method for short bolts connecting the rotor disc drum structure of a fan or compressor. This verification method has a simple algorithm and high computational efficiency. It fully considers the influence of rotor bending deformation caused by rotor rotation centrifugal force, unbalance, gyro torque, etc., on the bolt strength loss. At the same time, it can guide the design of bolt specifications and tightening torque in the design stage, thereby improving design efficiency.

[0066] like Figure 1 As shown, the strength verification method for fan or compressor disc drum connecting bolts of this application includes the following steps:

[0067] The fan or compressor rotor mainly bears aerodynamic torque, centrifugal force, gravity, unbalanced load, and gyroscopic torque during operation. This embodiment uses a six-stage compressor rotor (N=6) as an example. Figure 2 As shown, the rotational speed of the entire compressor is n, and the concentrated masses of each stage rotor disc / drum assembly are respectively... The unbalance quantity is (This can be estimated based on the rotor balance accuracy level in the structural design), the rotor support span is... The distances from the center of mass of each level of the drum to the fulcrum 1 are respectively The radii of the centroids are respectively .

[0068] The loads at fulcrum 1 and fulcrum 2 caused by the inertial loads acting on the rotor by each stage of the disc drum. It can be characterized as:

[0069] (1)

[0070] In the formula, K is the rotor overload coefficient, which can be found in the mechanical design manual, and g is the gravitational acceleration.

[0071] The centrifugal load caused by the imbalance of each level of the drum causes the loads at fulcrum 1 and fulcrum 2. It can be characterized as:

[0072] (2)

[0073] Loads at fulcrum 1 and fulcrum 2 caused by the gyroscopic torque Mt It can be characterized as:

[0074] (3)

[0075] According to Equations 1, 2, and 3, the maximum bending moment at a bolted connection section (Lx distance from fulcrum 1) of the fan or compressor rotor can be characterized as:

[0076] (4)

[0077] Based on the characteristics of bolted connections, it can be known that the entire rotor's various stages of discs and drums are rigidly connected, therefore the bending moment... A normal stress is generated on section x. The magnitude distribution of the normal stress is shown in [the figure]. Figure 3 As shown, when the cross-section is subjected to tensile stress, the connection surface tends to "separate." At this time, the bolt bears tensile load. According to the bending normal stress distribution of the circular cross-section beam, the maximum diameter of the bolt connection cross-section is located at the maximum tensile stress σ1, which can be characterized as follows: (5)

[0078] In the formula, W Z Where D is the section modulus of bending resistance, and D is the maximum outer diameter of the annulus within the effective bolt clamping area. , The minimum inner diameter of the annulus within the effective bolt clamping area. , For the bolt installation pitch circle diameter, The nominal diameter of the bolt;

[0079] Therefore, under bending stress, the maximum tensile stress load F borne by a certain bolt is... w for:

[0080] (6)

[0081] In the formula, Z represents the number of bolts.

[0082] During rotor operation, the structure undergoes thermal deformation due to the temperature field. Furthermore, the materials used for the fan and compressor discs and connecting bolts in common aero-engines differ, resulting in additional temperature loads on the bolts under thermal loads. (7)

[0083] In the formula, For the thermal deformation of the mounting edge of the disc, For the thermal deformation of the bolt, Let be the static stiffness of the bolt.

[0084] For the fan / compressor rotor, the connecting bolts also need to transmit the aerodynamic torque of the fan / compressor blades. For the aero-engine fan / compressor rotor, torque is usually transmitted through the frictional force of the bolts being tightened. Therefore, the connecting bolts also need to bear the tensile stress required to transmit the torque. (8)

[0085] In the formula, for Figure 2 The starting torque required for each stage of the disks before the mid-x section; denoted as the coefficient of friction of the drum connecting surface.

[0086] According to equations 6, 7, and 8, the axial tensile force F that the disc-drum connecting bolts need to bear during operation is: (9)

[0087] To meet strength requirements, the stress borne by the connecting bolts must meet allowable requirements, namely:

[0088] (10)

[0089] In the formula, This represents the allowable stress value of the material. This is the bolt size factor. For manufacturing process coefficients, This is the coefficient of non-uniformity of force. The stress concentration factor at the notch is... For safety factors, all relevant parameters can be found in the structural design manual.

[0090] To ensure that the bolts do not come loose during connection, a bolt preload is required. satisfy:

[0091] (11)

[0092] In the formula, This is the residual preload coefficient. This refers to the relative stiffness coefficient of the bolted connection;

[0093] In the design process of a fan or compressor, the tightening torque of the nut can be further designed. The designed tightening torque M0 of the nut is: (12)

[0094] In the formula, H is the tightening torque coefficient (related to the thread structure parameters), and s is the correction coefficient. Both coefficients can be obtained from relevant standards.

[0095] The strength verification method for fan or compressor rotor disc drum connecting bolts proposed in this application is simple in process and highly efficient in calculation. It fully considers the influence of rotor bending deformation caused by rotor rotation centrifugal force, unbalance, gyro torque, etc. on bolt strength loss. This method can be used to guide the design of bolt specifications, tightening torque, etc. in the design stage of fan or compressor rotor, which can greatly improve design efficiency.

[0096] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for strength verification of bolts used in connecting fan or compressor disc drums, characterized in that, The method includes: Determine the loads at the front and rear support points caused by the inertial loads of each stage of the disc drum acting on the fan or compressor rotor, the loads at the front and rear support points caused by the centrifugal loads caused by the imbalance of each stage of the disc drum, and the loads at the front and rear support points caused by the gyro torque. The maximum bending moment of the fan or compressor rotor at a certain bolted connection section is obtained based on the load at the front and rear support positions. Based on the bending normal stress distribution of the circular cross-section beam and the maximum bending moment of the bolt connection section, the maximum tensile stress at the position of the maximum diameter of the bolt connection section is obtained. Under the action of this maximum tensile stress, the maximum tensile stress load borne by the bolt is obtained. Determine the temperature load generated by the connecting bolts of the fan or compressor rotor under temperature load, and the tensile stress required for the connecting bolts to bear the transmitted torque; The axial tensile force required for the disc-drum connection bolt during operation is obtained by summing the maximum tensile stress load, temperature load, and tensile stress required for torsion transmission of the bolt. The strength of the disc drum connecting bolts is verified by checking the relationship between the stress borne by the connecting bolts and the allowable requirements, as well as the bolt preload and nut tightening torque, to determine the axial tensile force that the connecting bolts need to bear during operation.

2. The strength verification method for fan or compressor disc drum connecting bolts as described in claim 1, characterized in that, The loads at the front and rear support points caused by the inertial loads acting on the fan or compressor rotor by each stage of the disc drum are: ； In the formula, Q i1 The load at the front support point caused by the inertial loads acting on the fan or compressor rotor by each stage of the disc drum; Q i2 The load at the rear support point caused by the inertial loads acting on the fan or compressor rotor by each stage of the disc drum; These represent the concentrated mass of each level of rotor disc drum assembly, with subscript N indicating the disc drum number; L is the span between the front and rear support points; These are the distances from the center of mass of each level of the drum to the front fulcrum; K is the rotor overload coefficient; g is the acceleration due to gravity.

3. The strength verification method for fan or compressor disc drum connecting bolts as described in claim 2, characterized in that, The centrifugal load caused by the imbalance of each level of the drum results in the loads at the front and rear support points. ； In the formula, Q j1 The load at the front support point caused by the centrifugal load resulting from the imbalance of each level of the disc drum; Q j2 The load at the rear support point caused by the centrifugal load resulting from the imbalance of each level of the disc drum; These are the radii of the centroid of each level of the disc drum; n is the fan or compressor speed.

4. The strength verification method for fan or compressor disc drum connecting bolts as described in claim 3, characterized in that, The loads at the front and rear fulcrum positions caused by the gyroscopic torque are: ； In the formula, Q k1 The load at the front pivot point caused by the gyro torque; Q k2 The load at the rear pivot point caused by the gyro torque; Mt is the gyroscopic torque.

5. The strength verification method for fan or compressor disc drum connecting bolts as described in claim 4, characterized in that, The loads at the front and rear support points are used to obtain the maximum bending moment M of the fan or compressor rotor at a certain bolted connection section. x for: 。 6. The strength verification method for fan or compressor disc drum connecting bolts as described in claim 5, characterized in that, The maximum tensile stress at the location of the maximum diameter of the bolted connection section is: ； In the formula, D is the maximum outer diameter of the effective bolt clamping area annulus. , The minimum inner diameter of the annulus within the effective bolt clamping area. , For the bolt installation pitch circle diameter, The nominal diameter of the bolt; The maximum tensile stress load that the bolt can withstand under this maximum tensile stress is ； In the formula, Z represents the number of bolts.

7. The strength verification method for fan or compressor disc drum connecting bolts as described in claim 6, characterized in that, The temperature load generated by the connecting bolts is: ; In the formula, For the thermal deformation of the mounting edge of the disc, For the thermal deformation of the bolt, Let be the static stiffness of the bolt.

8. The strength verification method for fan or compressor disc drum connecting bolts as described in claim 7, characterized in that, The tensile stress required for the connecting bolts to transmit torque is: ； In the formula, The starting torque required for each stage of the disks before section x; denoted as the coefficient of friction of the drum connecting surface.

9. The strength verification method for fan or compressor disc drum connecting bolts as described in claim 8, characterized in that, The relationship between the stress σ borne by the connecting bolts and the allowable requirement is as follows: ； In the formula, This refers to the allowable stress value of the material. This is the bolt size factor; This refers to the manufacturing process coefficient; This is the coefficient for non-uniformity of stress. The notch stress concentration factor; This is for the safety factor.

10. The strength verification method for fan or compressor disc drum connecting bolts as described in claim 9, characterized in that, Bolt preload satisfy: ; In the formula, This is the residual preload coefficient. This refers to the relative stiffness coefficient of the bolted connection. The nut tightening torque M0 satisfies: ; In the formula, H is the tightening torque coefficient, and s is the correction coefficient.

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