Design method of binary nozzle vibration damping device

Abstract

The present invention provides a design method for a binary nozzle vibration damping device, which includes the following steps: establishing a three-dimensional model of the binary nozzle, calculating the natural frequency and vibration mode of the binary nozzle through finite element method, and evaluating the harmful vibration working condition points of the binary nozzle within the engine operating range under external excitation; arranging vibration damping tie rods at the elliptical nozzle, and the vibration damping tie rods are hollow thin-walled structures; setting the vibration damping tie rods in the finite element model, the vibration damping tie rods are beam elements, changing the control dimensions of the vibration damping tie rods, calculating the relationship between the tie rod structure and the natural frequency and vibration mode, avoiding the resonance frequency, and determining the optimal structure of the vibration damping tie rods. Through the design of the vibration damping tie rods, the present invention significantly improves the stiffness of the nozzle, enables the natural frequency of the nozzle to avoid harmful resonance; can enable the nozzle to meet the high-cycle fatigue life and improve the reliability of the engine; can be extended to the vibration suppression or frequency modulation fields of other special-shaped nozzles or structures.

Description

Technical Field

[0001] The present invention relates to the technical field of aeroengine design, and particularly to a design method for a vibration damping device at the nozzle of a two-dimensional nozzle. Background Art

[0002] The integrated design of aircraft engines is the development direction of future fighter jets. Stealth aircraft such as the US X-47B, F117, and B2 no longer show the characteristics of the traditional circular convergent tail nozzle of aeroengines from the appearance, but rather an irregular-shaped nozzle that coordinates with the aircraft's aerodynamics and stealth.

[0003] The fixed elliptical two-dimensional nozzle is involved for the first time in China. When the natural frequency of the nozzle coincides with the common rotational speed of the engine, it will cause intensified vibration, which is considered harmful resonance. Therefore, the vibration problem of the irregular-shaped nozzle is more prominent than that of the circular nozzle, and a vibration damping structure needs to be designed to eliminate or suppress vibration. Summary of the Invention

[0004] To solve the above technical problems, the present invention provides a design method for a two-dimensional nozzle vibration damping device.

[0005] The present invention is achieved through the following technical solutions.

[0006] The design method for a two-dimensional nozzle vibration damping device provided by the present invention includes the following steps:

[0007] Step 1: Establish a three-dimensional model of the two-dimensional nozzle, calculate the natural frequency and vibration mode of the two-dimensional nozzle through finite element method, and evaluate the harmful vibration working condition points of the two-dimensional nozzle within the engine operating range under external excitation;

[0008] Step 2: Set vibration damping tie rods at the elliptical nozzle. The vibration damping tie rods are of a hollow thin-wall structure;

[0009] Step 3: Set the vibration damping tie rods in the finite element model. The vibration damping tie rods are beam elements. Respectively change the control dimensions of the vibration damping tie rods, and calculate the relationship between the tie rod structure and the natural frequency and vibration mode, avoid the resonance frequency, and determine the optimal structure of the vibration damping tie rods.

[0010] The cross-section of the vibration damping tie rod is a smooth water droplet shape; in Step 3, the control dimensions include the following variables: leading edge radius R1, plate thickness δ, tie rod side radius R2, tie rod axial length L1, distance from the trailing edge of the tie rod to the rear end face of the nozzle L2, and tie rod installation angle θ. While increasing the stiffness of the nozzle, reduce the vibration caused by the friction of the air flow on the vibration damping nozzle to avoid intensified vibration; by respectively controlling each control dimension, it is convenient to deal with various forms of nozzles, determine their sensitive variables, and accurately control their natural frequencies through design to effectively avoid harmful resonance.

[0011] Step 3 includes the following steps: a. Determine the value ranges of each variable according to the requirements of the nozzle blockage area, give initial values, solve the relationship between each variable and the natural frequency of the nozzle through finite element method, and draw curves; b. Analyze the sensitivity of the influence of each variable on the natural frequency of the nozzle, sort the sensitive variables, and eliminate the insensitive variables; c. Give initial values again, solve the relationship between each sensitive variable and the natural frequency and vibration mode of the nozzle, and draw curves; d. Change the sensitive variables respectively, stay at the common rotational speed range and common rotational speeds of the engine, conduct resonance inspection, remove the value ranges of the sensitive variables corresponding to the harmful resonance points, and the remaining value ranges of the sensitive variables are the optimal value ranges.

[0012] Determine the value ranges of each variable according to the requirements of the nozzle blockage area, give initial values, where the leading edge radius R1 = [10 mm, 20 mm], the axial length of the pull rod L1 = [100 mm, 400 mm], and the side radius of the pull rod The distance L2 from the trailing edge of the pull rod to the rear end face of the nozzle is L2 = [0 mm, 100 mm]; the installation angle θ of the pull rod is θ = [45°, 50°].

[0013] The given initial values are: the leading edge radius R1 = 10 mm; the axial length of the pull rod L1 = 100 mm; the side radius of the pull rod R2 = 410 mm, the distance L2 from the trailing edge of the pull rod to the rear end face of the nozzle is 0; the installation angle θ of the pull rod is 45°.

[0014] In step c, the maximum rotational speed of the engine rotor is 14,000 revolutions per minute, and the common rotational speeds are 30%, 50%, 65%, 88%, 95% and 101%, and the corresponding frequencies are 70 Hz, 117 Hz, 152 Hz, 205 Hz, 222 Hz, 236 Hz in sequence.

[0015] The material of the vibration damping pull rod is TA15 titanium alloy, and the plate thickness δ = 1.5 mm.

[0016] The beneficial effects of the present invention are as follows:

[0017] Through the design of the vibration damping pull rod, the present invention significantly improves the stiffness of the nozzle, and makes the natural frequency of the nozzle avoid the resonance points of the common rotational speeds of the engine. The development and implementation of the nozzle vibration suppression technology can enable the nozzle to meet the high-cycle fatigue life and improve the reliability of the engine. In addition, the present invention can be extended to the vibration suppression or frequency modulation fields of other special-shaped nozzles or structures. Brief Description of the Drawings

[0018] Figure 1 is the installation schematic diagram of the dual-nozzle and the vibration damping pull rod of the present invention.

[0019] Figure 2 is the schematic diagram of the installation angle of the vibration damping pull rod.

[0020] Figure 3 It is a schematic cross-sectional view of a vibration damping tie rod.

[0021] Figure 4 It is a design flow chart of the present invention.

[0022] Figure 5 It is a schematic diagram of the natural frequency and vibration mode of the binary nozzle before improvement.

[0023] Figure 6 It is a schematic diagram of the natural frequency and vibration mode of the binary nozzle after improvement.

[0024] Figure 7 It is a schematic diagram of the natural frequency and vibration mode of the opening / closing vibration mode of the nozzle orifice of the binary nozzle before improvement.

[0025] Figure 8 It is a schematic diagram of the natural frequency and vibration mode of the opening / closing vibration mode of the nozzle orifice of the binary nozzle after improvement.

[0026] In the figure: 1 - nozzle body; 2 - elliptical nozzle orifice; 3 - vibration damping tie rod; R1 - leading edge radius of the tie rod; R2 - side radius of the tie rod; L1 - axial length of the tie rod; L2 - distance from the trailing edge of the tie rod to the rear end face of the nozzle orifice; θ - installation angle of the tie rod; δ - plate thickness. Specific implementation manner

[0027] The technical solution of the present invention will be further described below, but the scope of protection claimed is not limited thereto.

[0028] See Figures 1 to 4 :

[0029] Among the concepts used below: The leading edge radius R1 of the tie rod refers to the radius of curvature of the cross-section of the vibration damping tie rod 3 on the side facing the airflow direction; the side radius R2 of the tie rod refers to the radius of curvature of both sides of the cross-section of the vibration damping tie rod 3; the axial length L1 of the tie rod refers to the length of the cross-section of the vibration damping tie rod 3; the distance L2 from the trailing edge of the tie rod to the rear end face of the nozzle orifice, when the elliptical nozzle orifice 2 is parallel to the vibration damping tie rod 3, that is, the distance between the tip of the cross-section and the rear end of the elliptical nozzle orifice 2, and when the elliptical nozzle orifice 2 is not parallel to the vibration damping tie rod 3, it is the closest distance; the installation angle θ of the tie rod, the upper and lower ends of the vibration damping tie rod 3 are respectively connected to the elliptical nozzle orifice 2, and the angle between the vibration damping tie rod 3 and the axis of the nozzle body 1 is the installation angle, with a value range of 0° to 90°; the plate thickness δ refers to the thickness of the vibration damping nozzle.

[0030] The present invention provides a design method for a binary nozzle vibration damping device, including the following steps:

[0031] Step 1: Establish a three-dimensional model of the binary nozzle, calculate the natural frequency and vibration mode of the binary nozzle through finite element method, and evaluate the harmful vibration working condition points of the binary nozzle within the engine operating range under external excitation;

[0032] Step 2: Set up vibration damping tie rods 3 at the elliptical nozzle 2. The vibration damping tie rods 3 are of a hollow thin-walled structure.

[0033] Step 3: Set up the vibration damping tie rods 3 in the finite element model. The vibration damping tie rods 3 are beam elements. Respectively change the control dimensions of the vibration damping tie rods 3, and calculate the relationship between the tie rod structure and the natural frequency and vibration mode, avoid the resonance frequency, and determine the optimal structure of the vibration damping tie rods 3.

[0034] When the natural frequency of the nozzle coincides with the common rotational speed of the engine, it is considered harmful resonance. By changing the control dimensions, make the natural frequency of the nozzle avoid the resonance point of the common rotational speed of the engine, and the avoidance amplitude is 10% of the resonance frequency. This process is called harmful resonance inspection. After removing the value range of the control dimensions corresponding to the harmful resonance points, the remaining value range of the control dimensions is the optimal value range, and the structure of the vibration damping tie rods 3 corresponding to the optimal value range is the optimal structure.

[0035] Through the design of the vibration damping tie rods 3 of the present invention, the stiffness of the nozzle is significantly improved, and the natural frequency of the nozzle avoids the resonance point of the common rotational speed of the engine. The development and implementation of the nozzle vibration suppression technology can make the nozzle meet the high-cycle fatigue life and improve the reliability of the engine. In addition, the present invention can be extended to the vibration suppression or frequency modulation fields of other special-shaped nozzles or structures.

[0036] The cross-section of the vibration damping tie rods 3 is a smooth water droplet shape; in Step 3, the control dimensions include the following variables: leading edge radius R1, plate thickness δ, tie rod side radius R2, tie rod axial length L1, distance L2 from the trailing edge of the tie rod to the rear end face of the nozzle, and tie rod installation angle θ. While increasing the stiffness of the nozzle, reduce the vibration caused by the friction of the air flow on the vibration damping nozzle and avoid the aggravation of vibration; by respectively controlling each control dimension, it is convenient to deal with various forms of nozzles, determine their sensitive variables, and accurately control their natural frequencies through design to effectively avoid harmful resonance.

[0037] Step 3 includes the following steps: a. Determine the value ranges of each variable according to the requirements of the nozzle blockage area, give the initial values, solve the relationship between each variable and the natural frequency of the nozzle through finite element method, and draw the curves; b. Analyze the sensitivity of the influence of each variable on the natural frequency of the nozzle, sort the sensitive variables, and eliminate the insensitive variables; c. Give the initial values again, solve the relationship between each sensitive variable and the natural frequency and vibration mode of the nozzle, and draw the curves; d. Change the sensitive variables respectively, stay at the common engine speeds and within the common engine speed range, conduct resonance checks, remove the value ranges of the sensitive variables corresponding to the harmful resonance points, and the remaining value ranges of the sensitive variables are the optimal value ranges. The sensitive variables are defined as the variables whose value changes have an obvious influence on the natural frequency of the nozzle, and vice versa, they are called insensitive variables; by eliminating the insensitive variables and changing the sensitive variables respectively, the value ranges of the sensitive variables corresponding to the harmful resonance points are removed, so that the natural frequency of the nozzle avoids the resonance points at the common engine speeds; at the same time, the designed elasticity of the vibration damping rod 3 is ensured.

[0038] Determine the value ranges of each variable according to the requirements of the nozzle blockage area, give the initial values, where the leading edge radius R1 = [10 mm, 20 mm], the axial length of the rod L1 = [100 mm, 400 mm], the side radius of the rod The distance L2 from the trailing edge of the rod to the rear end face of the nozzle = [0 mm, 100 mm]; the installation angle θ of the rod = [45°, 50°].

[0039] The given initial values are: the leading edge radius R1 = 10 mm; the axial length of the rod L1 = 100 mm; the side radius of the rod R2 = 410 mm, the distance L2 from the trailing edge of the rod to the rear end face of the nozzle = 0; the installation angle θ of the rod = 45°.

[0040] Through steps a and b, within the given value ranges of each variable, starting from the initial variables, gradually increase each variable, solve the relationship between each variable and the natural frequency of the nozzle through finite element method, and draw the curves to determine the sensitive variables and their sorting; then through steps c and d, take values on the curves respectively, stay at the common engine speeds and within the common engine speed range, conduct resonance checks, remove the value ranges of the sensitive variables corresponding to the harmful resonance points, and the remaining value ranges are the optimal value ranges, thus completing the design of the vibration damping rod 3.

[0041] In step c, the maximum speed of the engine rotor is 14,000 revolutions per minute, and the common speeds are 30%, 50%, 65%, 88%, 95% and 101%, and the corresponding frequencies are 70 Hz, 117 Hz, 152 Hz, 205 Hz, 222 Hz, 236 Hz respectively.

[0042] Using the improvement of the dual-nozzle structure of the present invention, the comparison of the natural frequencies and vibration modes before and after is shown in Figures 5 to 8. A vibration sensor is set at the nozzle edge for experimental verification. The maximum engine speed is 14,000 revolutions per minute. It stays for 3 minutes at 30%, 50%, 65%, 88%, 95% and 101% of the maximum speed respectively for data collection, and the vibration frequency and mode of the engine nozzle are measured. Sweep the frequency in the range of [0 Hz to 300 Hz] at a speed of 1 Hz / 3 s to obtain the resonance points and vibration modes of each order of the nozzle. Among the first 6 natural frequencies of the dual nozzle, the 5th order coincides with 30% of the engine speed. As Figure 5 shown, there is a possibility of resonance; through the design of the present invention, the natural frequency after the structural improvement is increased to 74 Hz. As Figure 6 shown, it avoids the resonance point by 6%. For the nozzle opening / closing vibration mode, the pull rod significantly improves the stiffness of the nozzle. Under this vibration mode, the natural frequency is increased from 81 Hz to 99 Hz. As Figure 7 、 8 shown, it is increased by 22%.

[0043] The material of the damping pull rod 3 described above is TA15 titanium alloy, and the plate thickness δ = 1.5 mm.

Claims

1. A design method for a binary nozzle vibration damping device, characterized in that: It includes the following steps: Step 1: Establish a three-dimensional model of a two-dimensional nozzle. Calculate the natural frequency and vibration mode of the two-dimensional nozzle through finite element method, and evaluate the harmful vibration working condition points of the two-dimensional nozzle within the engine operating range under external excitation; Step 2: Set up vibration damping tie rods (3) at the elliptical nozzle (2). The vibration damping tie rods (3) are of hollow thin-walled structure; Step 3: Set up the vibration damping tie rods (3) in the finite element model. The vibration damping tie rods (3) are beam elements. Respectively change the control dimensions of the vibration damping tie rods (3), and calculate the relationship between the tie rod structure and the natural frequency and vibration mode, avoid the resonance frequency, and determine the optimal structure of the vibration damping tie rods (3).

2. The design method of the binary nozzle vibration damping device according to claim 1, characterized in that: The cross-section of the vibration damping tie rod (3) is a smooth water droplet shape; In step 3, the control dimensions include the following variables: leading edge radius (R1), plate thickness (δ), tie rod side radius (R2), tie rod axial length (L1), distance from the trailing edge of the tie rod to the rear end face of the nozzle (L2), and tie rod installation angle (θ).

3. The design method of the dual-nozzle vibration damping device according to claim 2, characterized in that: Step 3 includes the following steps: a. Determine the value range of each variable according to the nozzle blockage area requirement, give the initial values, solve the relationship between each variable and the natural frequency of the nozzle through finite element method, and draw curves; b. Analyze the sensitivity of the influence of each variable on the natural frequency of the nozzle, sort the sensitive variables, and eliminate the insensitive variables; c. Give the initial values again, solve the relationship between each sensitive variable and the natural frequency and vibration mode of the nozzle, and draw curves; d. Respectively change the sensitive variables, stay at the common engine speeds and within the common engine speed range, conduct resonance checks, remove the value ranges of the sensitive variables corresponding to the harmful resonance points, and the remaining value ranges of the sensitive variables are the optimal value ranges.

4. The design method of the binary nozzle vibration damping device according to claim 3, characterized in that: The value ranges of each variable are determined according to the requirements of the nozzle blockage area, and the initial values are given. Among them, the leading edge radius (R1) = [10 mm, 20 mm], the axial length of the pull rod (L1) = [100 mm, 400 mm], and the radius of the side surface of the pull rod The distance from the trailing edge of the pull rod to the rear end face of the nozzle (L2) = [0 mm, 100 mm]; the installation angle of the pull rod (θ) = [45°, 50°].

5. The design method of the binary nozzle vibration damping device according to claim 4, characterized in that: The given initial values are: leading edge radius (R1) = 10 mm; tie rod axial length (L1) = 100 mm; tie rod side radius (R2) = 410 mm, distance from the trailing edge of the tie rod to the rear end face of the nozzle (L2) = 0; tie rod installation angle (θ) = 45°.

6. The design method of the binary nozzle vibration damping device according to claim 3, characterized in that: In step c, the maximum rotational speed of the engine rotor is 14,000 revolutions per minute, and the common engine speeds are 30%, 50%, 65%, 88%, 95% and 101%, and the corresponding frequencies are 70 Hz, 117 Hz, 152 Hz, 205 Hz, 222 Hz, 236 Hz respectively.

7. The design method of the binary nozzle vibration damping device according to claim 1 or 2, characterized in that: The material of the vibration damping tie rod (3) is TA15 titanium alloy, and the plate thickness (δ) = 1.5 mm.

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