Modal Test Design Method for a Thin-Walled Casing with Lobed Rings under the Condition of Whole-Machine Assembly

Abstract

The present invention relates to the technical field of structural modal test design, and discloses a modal test design method under the condition of the overall assembly of a thin-walled casing with lobed integral ring. Based on the finite element analysis method, the modal calculation of a sector block of the thin-walled casing with lobed integral ring is carried out to determine the installation positions of measuring points in each region, and the main modes are determined based on the modal calculation results and the measuring point positions; the points with the largest vibration radial displacement of the thin-walled casing with lobed integral ring in each main mode are selected as excitation points, and the modal information of the casing can be obtained through the sensors on the measuring points during the knocking process. The present invention can improve the efficiency and accuracy of modal analysis, provide data support for the high-cycle fatigue resistance design of the thin-walled casing with lobed integral ring, and at the same time, without special tooling fixtures, the measurement can be carried out along with the overall machine test, which not only improves the test efficiency, but also saves the test labor and material costs.

Description

Technical Field

[0001] The present invention relates to the technical field of structural modal test design, and discloses a modal test design method under the condition of the overall assembly of a lobe-integrated thin-walled casing. Background Art

[0002] In order to improve the thrust-to-weight ratio, lobe-integrated thin-walled casings (as shown in Figure 1 ) are widely used in aeroengines. This structure is exposed to high-temperature, high-pressure, and high-speed airflows. Its lobe structure can reduce the steady-state thermal stress by generating thermal deformation. However, the relatively weak-rigid lobe structure is prone to vibration caused by airflow excitation, resulting in relatively high vibration stress. Therefore, high-cycle fatigue cracks caused by vibration often occur.

[0003] In order to prevent high-cycle fatigue cracks from occurring in the lobe-integrated thin-walled casing, anti-high-cycle fatigue design needs to be implemented on it. The first step is to accurately obtain the natural frequency, vibration mode, and damping through modal tests. Although the modal test design method for the casing has been very mature, the current modal test design method mainly targets the casing in the component state. Special tooling needs to be designed to simulate the overall assembly environment, which increases the test cost and prolongs the test cycle. At the same time, the assembly constraint situation between the lobe-integrated thin-walled casing and the whole machine is relatively complex, resulting in it being difficult to simulate the constraint boundary of the casing under the condition of the overall machine assembly through simple component modal testing. Therefore, the component modal test not only takes a lot of time, but also the results often have relatively large errors, resulting in low accuracy of the vibration design results of the lobe-integrated thin-walled casing. In addition, the modal test layout under the condition of the overall machine assembly is restricted by space and there cannot be too many measuring points, making it easy to miss the modes that designers are concerned about, resulting in poor test effects. Summary of the Invention

[0004] The purpose of the present invention is to provide a modal test design method under the condition of the overall assembly of a lobe-integrated thin-walled casing, which can improve the efficiency and accuracy of modal analysis, provide data support for the anti-high-cycle fatigue design of the lobe-integrated thin-walled casing, and does not require special tooling fixtures. Measurements can be carried out along with the overall machine test, which not only improves the test efficiency but also saves the test labor and material costs.

[0005] In order to achieve the above technical effects, the technical solution adopted by the present invention is:

[0006] A modal test design method under the condition of the overall assembly of a lobe-integrated thin-walled casing, comprising:

[0007] According to the center point positions of the mounting holes in the mounting hole rows of the connecting parts on the lobe-integrated thin-walled casing, the lobe-integrated thin-walled casing is axially divided into regions, where is the number of mounting hole rows of the connecting parts;

[0008] Perform modal calculations on a sector of the lobe-ring thin-walled casing based on the finite element analysis method to obtain the total number of orders and the total number of nodal diameters of the lobe-ring thin-walled casing, as well as the relative vibration radial displacement of each node in the sector under different orders for each nodal diameter vibration;

[0009] Based on the relative vibration radial displacement of each node under different orders for each nodal diameter vibration, obtain the equivalent vibration radial displacement of each node in each region, and take the position where the point with the maximum equivalent vibration radial displacement in each region is located as the installation position of the measurement point in that region;

[0010] Based on the relative vibration radial displacement of each measurement point under different orders for each nodal diameter vibration and the average equivalent vibration radial displacement of the corresponding measurement point, analyze and obtain the radial displacement coefficient of each measurement point, and select the modal vibration in which the radial displacement coefficients of all measurement points are greater than the preset coefficient threshold as the main mode;

[0011] Select the point with the maximum vibration radial displacement of the lobe-ring thin-walled casing in each main mode as the excitation point, and sequentially strike each excitation point during the test. The striking direction is the radial direction of the casing to obtain the modal information of the casing through the sensors on the measurement points.

[0012] Furthermore, before the modal calculation process, determine in advance the structural components that excite the lobe-ring thin-walled casing according to the installation position of the lobe-ring thin-walled casing of the aero-engine; the lobe-ring thin-walled casing is fixedly installed at the outlet of the low-pressure turbine through a connecting piece, and the structural components include low-pressure turbine rotor blades, turbine rear struts, and fuel injection rods;

[0013] Based on the structural component with the largest number in the structural components and the low-pressure rotor fundamental frequency corresponding to the highest steady-state physical speed, analyze and obtain the highest calculation frequency of the lobe-ring thin-walled casing Analyze and obtain, where is the number of low-pressure turbine rotor blades, is the number of turbine rear struts, is the number of the fuel injection rod closest to the casing, is the low-pressure rotor fundamental frequency corresponding to the highest steady-state physical speed.

[0014] Furthermore, the equivalent vibration radial displacement of each node in each region , where is the maximum vibration order value of the casing with a vibration frequency less than the highest calculation frequency, is the number of circumferentially symmetric sectors of the casing, is the corresponding node at the th order and the th nodal diameter vibration relative vibration radial displacement.

[0015] Furthermore, the average equivalent vibration radial displacement of the measurement point 。

[0016] Furthermore, the radial displacement coefficient of the measuring point is obtained according to analysis, where is the radial displacement coefficient of the corresponding measuring point.

[0017] Furthermore, the preset coefficient threshold value is taken as 1.

[0018] Furthermore, the number of excitation points is determined according to where is the number of excitation points, is the determined number of main modes.

[0019] Furthermore, after the number and position of the excitation points are determined, the excitation points are numbered according to the ascending order of the main mode frequencies. During the test, each excitation point is struck in sequence according to the numbering order, and the striking direction is the radial direction of the casing. At least one round of striking is repeated, and each excitation point is struck at least twice to obtain the modal information of the casing through the sensors on the measuring points.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention can improve the efficiency and accuracy of modal analysis, provide data support for the high-cycle fatigue resistance design of the thin-walled casing with lobed integral ring, and at the same time, without special tooling fixtures, the measurement can be carried out along with the whole machine test, which not only improves the test efficiency but also saves the test labor and material costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is a flowchart of the modal test design method for the thin-walled casing with lobed integral ring under the whole machine assembly condition in Embodiment 1 or 2;

[0022] Figure 2 is a schematic structural diagram of the thin-walled casing with lobed integral ring in Embodiment 1 or 2;

[0023] Figure 3 is a schematic cross-sectional view of the thin-walled casing with lobed integral ring in Embodiment 1 or 2;

[0024] Figure 4 is a schematic distribution diagram of the measuring points and excitation points in one fan block in Embodiment 2;

[0025] Among them, 1. Thin-walled casing with lobed integral ring; 2. Mounting hole; 301. Region 1; 302. Region 2; 303. Region 3; 4. Measuring point; 5. Excitation point; 6. Rectangular frame. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0026] The present invention will be further described in detail below in conjunction with embodiments and the accompanying drawings. However, it should not be understood that the scope of the above-mentioned subject matter of the present invention is limited to the following embodiments. All technologies implemented based on the content of the present invention belong to the scope of the present invention.

[0027] Embodiment 1

[0028] Refer to Figures 1 - 3 , the modal test design method for the whole machine assembly of a lobe-integrated thin-walled casing, including:

[0029] According to the center point positions of the mounting holes 2 in the row of mounting holes 2 on the lobe-integrated thin-walled casing 1, the lobe-integrated thin-walled casing 1 is axially divided into regions, where is the number of rows of the mounting holes 2 of the connecting piece;

[0030] Based on the finite element analysis method, the modal calculation is carried out on a sector of the lobe-integrated thin-walled casing 1 to obtain the total number of orders and the total number of nodal diameters of the lobe-integrated thin-walled casing 1, as well as the relative vibration radial displacement of each node in the sector under different orders for each nodal diameter vibration;

[0031] According to the relative vibration radial displacement of each node under different orders for each nodal diameter vibration, the equivalent vibration radial displacement of each node in each region is obtained , and the position where the point with the largest equivalent vibration radial displacement in each region is located is taken as the installation position of the measuring point 4 in this region;

[0032] According to the relative vibration radial displacement of each measuring point 4 under different orders for each nodal diameter vibration, and the average equivalent vibration radial displacement corresponding to the measuring point 4 , the radial displacement coefficient of each measuring point 4 is analyzed and obtained , and the modal vibration with the radial displacement coefficients of all measuring points 4 being greater than the preset coefficient threshold is selected as the main mode;

[0033] The point with the largest vibration radial displacement of the lobe-integrated thin-walled casing 1 in each main mode is selected as the excitation point 5. During the test, each excitation point 5 is tapped in turn, and the tapping direction is the radial direction of the casing, so as to obtain the modal information of the casing through the sensor on the measuring point 4.

[0034] ​In this embodiment, based on the finite element analysis method, a modal calculation is performed on a fan segment of the lobed integral thin-walled casing 1 to obtain the total number of orders and the total number of nodal diameters of the lobed integral thin-walled casing 1, as well as the relative vibration radial displacement of each node in the fan segment under different orders for each nodal diameter vibration; then, according to the relative vibration radial displacement of each node under different orders for each nodal diameter vibration, the equivalent vibration radial displacement of each node in each region is obtained to determine the installation position of the measuring point 4 in each region, and the main mode is determined based on the modal calculation result and the position of the measuring point 4; the point with the largest vibration radial displacement in each main mode of the lobed integral thin-walled casing 1 is selected as the excitation point 5, and the modal information of the casing can be obtained through the sensor on the measuring point 4 during the knocking process. This embodiment can accurately obtain the modal parameters of the lobed integral thin-walled casing 1 under the whole machine assembly conditions, and the number of required measuring points 4 is small. While improving the efficiency and accuracy of modal analysis and providing data support for the high cycle fatigue resistance design of the lobed integral thin-walled casing 1, no special tooling fixture is required, and the measurement can be carried out along with the whole machine test, which not only improves the test efficiency but also saves the test labor and material costs.

[0035] Embodiment 2

[0036] See Figures 1 - 4 , a modal test design method for the lobed integral thin-walled casing under the whole machine assembly conditions of an aeroengine, including:

[0037] Step 1: Determine the structural components that generate excitation for the lobed integral thin-walled casing 1 according to the installation position of the lobed integral thin-walled casing 1 of the aeroengine; the lobed integral thin-walled casing 1 is fixedly installed at the outlet of the low-pressure turbine through a connecting piece, and the structural components include low-pressure turbine rotor blades, turbine rear struts, and fuel injection rods;

[0038] Before performing the modal calculation based on the finite element, it is first necessary to determine the highest calculation frequency. For example, in this embodiment, the lobed integral thin-walled casing 1 is located at the outlet of the low-pressure turbine, and potential excitation factors such as low-pressure turbine rotor blades, turbine rear struts, and fuel injection rods should be considered at this time.

[0039] Step 2: Analyze and obtain the highest calculation frequency of the lobed integral thin-walled casing 1 according to the structural component with the largest number in the structural components and the low-pressure rotor fundamental frequency corresponding to the highest steady-state physical rotation speed;

[0040] In this embodiment, since structural components such as low-pressure turbine rotor blades, turbine rear struts, and fuel injection rods are potential excitation factors for the lobed integral thin-walled casing 1, the highest calculation frequency is determined , where is the number of low-pressure turbine rotor blades, is the number of turbine rear struts, is the number of the fuel injection rod closest to the casing, is the fundamental frequency of the low-pressure rotor corresponding to the highest steady-state physical speed (unit: Hz).

[0041] Step 3: Divide the lobed integral thin-walled casing 1 axially into regions according to the center point positions of the mounting holes 2 in the row of mounting holes 2 on the lobed integral thin-walled casing 1, where is the number of rows of the mounting holes 2 of the connecting piece;

[0042] The lobed integral thin-walled casing 1 generally has ( = 2, 3, 4...) rows of mounting holes 2 for the installation of pins. Therefore, in this embodiment, take lines passing through the centers of each row of mounting holes 2 and parallel to the air inlet edge of the casing as the demarcation lines, and divide the lobed integral thin-walled casing 1 axially into regions, and one measuring point 4 needs to be arranged in each region, that is, the total number of measuring points 4 is . The schematic diagram of the structural region division of the casing with two rows of pin holes is shown in Figure 4 , Figure 4 The structure shown is Figure 3 a single sector structure (01# lobe) in the rectangular frame 6, and the viewing angle is along the Figure 3 negative direction of the Z-axis. It should be noted that Region 1 301, Region 2 302, and Region 3 303 include the integral ring structure, Figure 4 only the parts of Region 1 301, Region 2 302, and Region 3 303 on one sector are shown.

[0043] Step 4: Perform modal calculation on one sector of the lobed integral thin-walled casing 1 based on the finite element analysis method to obtain the total number of orders and the total number of nodal diameters of the lobed integral thin-walled casing 1, as well as the relative vibration radial displacement of each nodal diameter vibration of each node in the sector at different orders; where the highest frequency in the modal calculation process is greater than or equal to the highest calculation frequency;

[0044] Step 5: Obtain the equivalent vibration radial displacement of each node in each region according to the relative vibration radial displacement of each nodal diameter vibration of each node at different orders , and take the position where the point with the largest equivalent vibration radial displacement in each region is located as the installation position of the measuring point 4 in that region;

[0045] In this embodiment, the equivalent vibration radial displacement of each node in each region , where is the maximum vibration order value of the casing with a vibration frequency less than the highest calculation frequency, is the number of circumferentially symmetric sectors of the casing, is the corresponding node at the order at the The relative vibration radial displacement of the nodal diameter vibration.

[0046] Step Six: According to the relative vibration radial displacement of each nodal diameter vibration at different orders of each measuring point 4, and the average equivalent vibration radial displacement of the corresponding measuring point 4 , analyze and obtain the radial displacement coefficients of each measuring point 4 , select the radial displacement coefficients of all measuring points 4 whose values are all greater than the preset coefficient threshold as the main modal vibrations;

[0047] The modes of the thin-walled casing are relatively dense, and the radial vibration modes among them are the most harmful. Therefore, as long as the modal test can measure the modes mainly composed of radial vibration. In this embodiment, the modes mainly composed of radial vibration are defined as the main modes. The determination method of the main modes is as follows: On the basis of the determined position of the measuring point 4, define the radial displacement coefficient , where is the radial displacement coefficient of the corresponding measuring point 4, is the average equivalent vibration radial displacement of the measuring point 4, , select the radial displacement coefficients of all measuring points 4 whose values are all greater than 1 as the main modal vibrations.

[0048] Step Seven: Select the points with the largest vibration radial displacement in each main mode of the thin-walled casing 1 with a lobed integral ring as the excitation points 5, number the excitation points 5 in ascending order of the main mode frequencies, and when conducting the test, strike each excitation point 5 in sequence according to the numbering. The striking direction is the radial direction of the casing, repeat the striking at least once, and strike each excitation point 5 at least twice to obtain the modal information of the casing through the sensors on the measuring point 4;

[0049] In this embodiment, the number of excitation points 5 is determined according to , where is the number of excitation points 5, is the number of main modes determined in Step Six.

[0050] The above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. Modal test design method under the condition of overall assembly of a thin-walled casing with lobe integral ring, characterized in that Including: According to the center point positions of the mounting holes in the mounting hole rows of the connecting parts on the thin-walled casing with lobes, the thin-walled casing with lobes is axially divided into regions, where is the number of mounting hole rows of the connecting parts; Performing modal calculations on a sector of the lobe-integrated thin-walled casing based on the finite element analysis method to obtain the total number of orders and the total number of nodal diameters of the lobe-integrated thin-walled casing, as well as the relative vibration radial displacements of each node in the sector under different orders for each nodal diameter vibration; Based on the relative vibration radial displacements of each node under different orders for each nodal diameter vibration, obtaining the equivalent vibration radial displacements of each node in each region, and taking the position where the point with the maximum equivalent vibration radial displacement in each region is located as the installation position of the measurement point in that region; Based on the relative vibration radial displacements of each measurement point under different orders for each nodal diameter vibration and the corresponding average equivalent vibration radial displacement of the measurement point, analyzing and obtaining the radial displacement coefficients of each measurement point, and selecting the modal vibration in which the radial displacement coefficients of all measurement points are greater than the preset coefficient threshold as the main mode; Selecting the point with the maximum vibration radial displacement in each main mode of the lobe-integrated thin-walled casing as the excitation point, and sequentially knocking on each excitation point during the test, with the knocking direction being the radial direction of the casing, so as to obtain the modal information of the casing through the sensors on the measurement points.

2. The modal test design method under the overall assembly conditions of the lobe-integrated thin-walled casing according to claim 1, characterized in that Before the modal calculation process, determining in advance the structural components that excite the lobe-integrated thin-walled casing of the aero-engine according to the installation position of the lobe-integrated thin-walled casing; the lobe-integrated thin-walled casing is fixedly installed at the outlet of the low-pressure turbine through a connecting piece, and the structural components include low-pressure turbine rotor blades, turbine rear struts, and fuel injection rods; Analyze and obtain the highest calculated frequency of the lobed integral thin-walled casing based on the structural component with the largest quantity in the structural components and the fundamental frequency of the low-pressure rotor corresponding to the highest steady-state physical rotational speed Analyze and obtain, where is the number of low-pressure turbine rotor blades, is the number of turbine rear struts, is the number of fuel injection rods closest to the casing, is the fundamental frequency of the low-pressure rotor corresponding to the highest steady-state physical rotational speed.

3. The modal test design method under the whole machine assembly condition of the thin-walled casing with lobe integral ring according to claim 2, characterized in that Equivalent vibration radial displacement of each node in each region , where is the maximum vibration order value of the casing with a vibration frequency less than the highest calculated frequency, is the number of circumferentially symmetric sectors of the casing, is the relative vibration radial displacement of the corresponding node for the -th order and -th pitch diameter vibration.

4. The modal test design method under the overall assembly conditions of the lobe-integrated thin-walled casing according to claim 3, wherein, Average equivalent vibration radial displacement of measurement point .

5. The modal test design method under the overall machine assembly conditions of the thin-walled casing with lobe integral ring according to claim 4, characterized in that The radial displacement coefficient of the measuring point is obtained according to analysis, where is the radial displacement coefficient corresponding to the measuring point.

6. The modal test design method under the whole machine assembly condition of the thin-walled casing with lobe rings according to claim 1, wherein The preset coefficient threshold is taken as 1.

7. The modal test design method under the whole machine assembly condition of the thin-walled casing with lobed integral ring according to claim 1, characterized in that The number of excitation points is determined according to where is the number of excitation points, is the determined number of main modes.

8. The modal test design method under the overall assembly conditions of the lobe-integrated thin-wall casing according to claim 7, characterized in that After determining the number and positions of the excitation points, numbering the excitation points in ascending order of the main mode frequency, and sequentially knocking on each excitation point in the numbered order during the test, with the knocking direction being the radial direction of the casing, repeating the knocking at least once, and knocking each excitation point at least twice, so as to obtain the modal information of the casing through the sensors on the measurement points.

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