A fine flow field testing device and a probe natural frequency testing method

Abstract

The application belongs to the technical field of impeller machine test, and particularly relates to a fine flow field testing device and a probe natural frequency testing method. By adjusting the frequency and amplitude of a signal generator, the probe is swept frequency sound excited, the frequency leakage problem in the prior art is solved, the continuous sound excitation and laser displacement sensor vibration pickup method are adopted to solve the poor probe high-order natural frequency identification and capture problem in the prior art, the non-contact method is adopted to measure the natural frequency of the probe when the displacement mechanism is installed, the problem that a special tool needs to be processed in the prior art is solved, and the problem that the probe connection mode affects the natural frequency of the probe is solved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of impeller test, and particularly relates to a fine flow field testing device and a probe natural frequency testing method. BACKGROUND

[0002] The fine flow field measurement of a compressor is an important part of the performance test of the compressor. The high-precision static / dynamic aerodynamic probe is adjusted through a displacement mechanism to obtain the aerodynamic characteristic parameters such as the total pressure, static pressure, Ma and flow angle at the compressor interstage or outlet. The displacement mechanism includes three degrees of freedom components of X-axis (approximately circumferential of the blade passage), Y-axis (approximately radial of the blade passage) and rotation along the probe rod axis, which can adjust and control the probe in real time according to the flow characteristics of the flow field and the requirements of the test position.

[0003] Since the flow field of the compressor is relatively complex, the excitation frequency bandwidth is large during the test. When the excitation frequency is near the natural frequency of the probe, the vibration of the probe will suddenly increase, which may cause the failure of the probe and even damage the blade, threatening the safety of the test. The complexity of the connection form of the probe and the displacement mechanism leads to a large error in the calculation of the natural frequency of the probe by the finite element method, so that the strength of the probe cannot be accurately evaluated. There are mainly two kinds of test methods for the natural frequency of the probe at present: (1) the hammering method is used to excite the probe to obtain the natural frequency of the probe; (2) the random excitation and scanning excitation are used to excite the dynamic probe by the excitation table, and the natural frequency of the probe is obtained through the vibration pickup device. The existing technology has a large error in testing the natural frequency of the probe, and cannot evaluate the influence of the displacement mechanism on the response characteristics of the probe during use, so it is urgent to develop a high-precision and easy-to-operate probe natural frequency testing method for the fine flow field testing device of the compressor.

[0004] The existing technical solution one is that the fine flow field testing device is composed of a probe and a displacement mechanism. In the existing technical solution one, the sensor is mounted on the surface of the probe, the hammer is used to knock the probe, and the natural frequency of the probe is obtained. The existing technical solution one has the following disadvantages: the test results of the hammering method are disturbed by subjective factors such as knocking skills, and the test results may have the phenomenon of missing frequency, and the repeatability of the test results is poor; when the natural frequency is tested by the hammering method, the accuracy and recognition of the test results of the natural frequency at high frequency are low; the displacement mechanism and the probe are flexibly connected through a gasket, and the natural frequency obtained by the hammering method may be the natural frequency of the combined system of the probe and the displacement mechanism, and the natural frequency of the probe cannot be accurately identified.

[0005] The existing technical solution two is that in this existing technical solution, the structure to be tested is placed on the excitation table for random excitation and scanning excitation, and the natural frequency characteristics of the probe are picked up by a laser displacement sensor or other types of sensors.

[0006] The second prior art solution has the following disadvantages: when the excitation table tests the natural frequency of the probe, a matching tool needs to be processed according to the structure and size of the probe, and the test period is long; the probe and the excitation table are rigidly connected, and the probe and the displacement mechanism are flexibly connected through a gasket, and the difference in the connection mode will affect the test result of the natural frequency of the probe, and the natural frequency test of the probe by the excitation table cannot obtain the response characteristics of the probe in the use process. SUMMARY

[0007] To solve the above problems, the application provides a fine flow field test device, comprising:

[0008] a test bench;

[0009] a displacement mechanism for changing the extension length of the probe installed on the test bench;

[0010] an acoustic horn fixed on the test bench through a fixing frame, and the opening of the acoustic horn faces the probe;

[0011] a laser displacement sensor for measuring the vibration of the probe;

[0012] a signal power amplifier connected to the laser displacement sensor;

[0013] a dynamic acquisition system connected to the signal power amplifier; the dynamic acquisition system connects and controls the output frequency of the acoustic horn.

[0014] Preferably, an adapter is connected at the outlet of the acoustic horn, and the adapter comprises a gradually tapered tapering section and a flat section connected at the end of the tapering section.

[0015] A natural frequency test method, which uses the fine flow field test device to perform tests, comprising:

[0016] Step S1: the acoustic horn outputs noise excitation with gradually increasing frequency starting from the initial frequency F0 to the probe with the initial excitation position X0;

[0017] Step S2: simultaneously collect multiple time domain signals at the probe measurement point under the noise excitation with gradually increasing frequency through the laser displacement sensor;

[0018] Step S3: perform Fourier transform on the multiple time domain signals collected by the laser displacement sensor, extract single-frequency information of the frequency component, generate a frequency domain response curve, and obtain the natural frequency response characteristics of the probe;

[0019] Step S4: change the extension length of the probe through the displacement mechanism, and repeat steps S1 to S3; obtain the natural frequency response characteristics of the probe with different extension lengths.

[0020] Preferably, the laser displacement sensor is calibrated by a dynamic acquisition system before use.

[0021] Preferably, the time domain signal is filtered and purified by a Bessel filter to reduce the interference of electronic element current noise.

[0022] Preferably, the initial frequency F0 and the maximum frequency of the acoustic horn contain the theoretical inherent frequency range of the probe.

[0023] Preferably, the noise excitation of the acoustic horn is single-frequency noise, and the intensity of the single-frequency noise is at least 20 dB higher than the background noise intensity.

[0024] Preferably, the acquisition time of the laser displacement sensor for the probe under the same frequency single-frequency noise is 30 seconds.

[0025] The advantages of the present application include: by adjusting the frequency and amplitude of the signal generator, the probe is subjected to sweep frequency acoustic excitation, which solves the frequency leakage problem in the prior art; by using continuous acoustic excitation and laser displacement sensor vibration pickup method, the problem of poor identification and capture of high-order inherent frequency of the probe in the prior art is solved; by using non-contact method to measure the inherent frequency of the probe when the displacement mechanism is installed, the problem of needing to process special tooling in the prior art is solved, and the problem of the influence of the probe connection method on the inherent frequency of the probe is also solved. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 is a schematic diagram of a refined flow field test device according to a preferred embodiment of the present application. DETAILED DESCRIPTION

[0027] In order to make the technical solutions of the present application and its advantages clearer, the technical solutions of the present application will be further described in detail below with reference to the drawings. It should be understood that the specific embodiments described herein are only part of the embodiments of the present application, and are only used to explain the present application, but not to limit the present application. It should be noted that, for the purpose of description, only parts related to the present application are shown in the drawings, and other related parts can be referred to the usual design. In the case of no conflict, the embodiments in the present application and the technical features in the embodiments can be combined to obtain new embodiments.

[0028] In addition, unless otherwise defined, technical terms or scientific terms used in the description of the application shall be understood as the common meaning understood by one of ordinary skill in the art to which the application belongs. The words "upper", "lower", "left", "right", "center", "vertical", "horizontal", "inner", "outer" and the like used in the description of the application only indicate relative directions or positional relationships, and do not imply that the device or element must have a particular orientation, be constructed and operated in a particular orientation, and when the absolute position of the described object changes, the relative positional relationship may also change accordingly, so it cannot be understood as a limitation on the application. The "first", "second", "third" and the like used in the description of the application are only for the purpose of description, to distinguish different components, and cannot be understood as indicating or implying relative importance. The "one", "a" or "the" and the like used in the description of the application should not be understood as an absolute limitation on the quantity, but should be understood as the presence of at least one. The "includes" or "contains" and the like used in the description of the application means that the elements or objects appearing before the word are covered by the elements or objects listed after the word and their equivalents, without excluding other elements or objects.

[0029] In addition, it should be further pointed out that, unless otherwise explicitly specified and limited, the "installation", "connection", "connection" and the like used in the description of the application should be understood in a broad sense, for example, the connection can be fixed connection, or detachable connection, or integral connection; can be mechanical connection, or electrical connection; can be directly connected, or indirectly connected through intermediate medium, or the internal communication of two elements, and those skilled in the art can understand the specific meaning of the application according to the specific circumstances.

[0030] The application adjusts the frequency and amplitude of the signal generator to sweep the probe with sound excitation, solves the problem of missing frequency in the prior art solution of knocking method, uses continuous sound excitation and laser displacement sensor vibration pickup method to solve the problem of poor identification and capture of high-order natural frequency of the probe in the prior art, uses non-contact method to measure the natural frequency of the probe when the displacement mechanism is installed, solves the problem of needing to process special tooling in the prior art, and at the same time solves the problem of the influence of the connection mode of the probe on the natural frequency of the probe.

[0031] Specifically, as Figure 1As shown, a fine flow field testing device, the testing device is composed of sound excitation device, response collection device and fixed bench. The sound excitation device is composed of acoustic horn, power amplifier and signal generator, the response collection device is composed of laser displacement sensor, dynamic collection system and data analysis software. Specifically comprising: test bench; displacement mechanism 5 for changing the extension length of probe 4 installed on the test bench; acoustic horn 1 fixed on the test bench through fixing frame 3, the opening of acoustic horn 1 faces probe 4; laser displacement sensor 6 for measuring the vibration of probe 4; signal power amplifier 7 connected with laser displacement sensor 6; dynamic collection system 8 connected with signal power amplifier 7; dynamic collection system 8 connects and controls the output frequency of acoustic horn 1; the outlet of acoustic horn 1 is connected with adapter 2, adapter 2 includes gradually shrinking shrinkage section and flat section connected at the end of shrinkage section.

[0032] Among them, adapter 2 is designed according to the size of acoustic horn 1, adapter 2 includes shrinkage section and flat section, the diameter of flat section needs to be designed according to the size of horn sound segment and scanning frequency, and the excitation sound source is a plane wave as much as possible, and the reflection and loss of noise in the adapter section pipeline are reduced.

[0033] Firstly, the initial frequency of noise excitation can be selected through the test system and according to the probe inherent frequency intensity calculation result, and it is ensured that the noise excitation scanning frequency range envelops the probe inherent frequency range as much as possible, the power amplifier parameters are adjusted according to the high sound intensity horn, and the single frequency noise with appropriate intensity is obtained, and the intensity of single frequency noise needs to be higher than the background noise intensity by more than 20dB.

[0034] Step 1 adjusts the relative position of laser displacement sensor and probe, and the laser displacement sensor is calibrated by using dynamic collection system.

[0035] Step 2 adjusts the initial frequency F0, amplitude P of noise excitation and the initial excitation position X0 of probe, collects the displacement of probe after adjusting stably, sets the collection time as 30S, continuously increases the frequency of noise excitation, and excites the probe X0 position by noise excitation, and collects the time domain characteristics of probe measuring point.

[0036] Step 3 carries out Fourier transform on the time domain signal collected by laser displacement sensor, selects Bessel filter to filter and purify the signal, and reduces the interference of electronic element current noise on the vibration signal.

[0037] Step 4 extracts the single frequency information including frequency and amplitude of the frequency component concerned from the mixed frequency information, generates frequency domain response curve, and obtains the inherent frequency of dynamic probe.

[0038] Step 5 adjusts the excitation position of the probe in the use process by the displacement mechanism, sequentially excites the probe with noise, and repeats steps 1 to 4 to obtain the inherent frequency response characteristics of the probe at different positions.

[0039] Step 6 analyzes and collates the collected data to obtain the inherent frequency characteristics of the probe in the approximate real working environment when the displacement mechanism is installed.

[0040] The beneficial effects of the present application are:

[0041] The sweep excitation of the probe by the sound excitation device can identify the inherent frequency of the probe, the identification result is not affected by the knocking skill, the inherent frequency of the probe can be objectively obtained, there is no risk of missing frequency, and no matching tooling device needs to be processed. The present application has obvious beneficial effects compared with the prior art.

[0042] The sweep excitation of the probe by the sound excitation device can improve the accuracy and recognition of the high-frequency inherent frequency identification of the dynamic probe.

[0043] The sound excitation method can effectively identify the inherent frequency of the probe when the displacement mechanism is installed, can consider the influence of the probe displacement mechanism on the response characteristics of the probe, and the result has more engineering application value.

[0044] When the sound excitation method is used to test the inherent frequency of the probe, the probe can be excited at different scanning excitation positions, so as to obtain the inherent frequency characteristics of the probe in the dynamic test process.

[0045] The above is only a specific embodiment of the present application, but the protection scope of the present application is not limited thereto. Any changes or replacements within the technical range disclosed in the present application can be easily thought of by those skilled in the art, which should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A method for testing natural frequencies, employing a refined flow field testing device, characterized in that, include: Test bench; Displacement mechanism (5) installed on the test bench to change the extension length of probe (4); The acoustic horn (1) is fixed to the test bench by the fixing bracket (3), and the opening of the acoustic horn (1) faces the probe (4). A laser displacement sensor (6) is used to measure the vibration of probe (4). A signal power amplifier (7) is connected to the laser displacement sensor (6); A dynamic acquisition system (8) is connected to the signal power amplifier (7); the dynamic acquisition system (8) is connected to and controls the output frequency of the acoustic speaker (1); An adapter (2) is connected to the outlet of the acoustic horn (1). The adapter (2) includes a gradually narrowing section and a straight section connected to the end of the narrowing section. The method includes: Step S1: The probe (4) with an initial excitation position of X0 is output with a noise excitation that gradually increases from the initial frequency F0 through the acoustic horn (1); Step S2: Simultaneously, multiple time-domain signals at the probe (4) measuring point are acquired by the laser displacement sensor (6) under noise excitation with gradually increasing frequency; Step S3: Perform Fourier transform on the multiple time-domain signals collected by the laser displacement sensor (6), extract the single-frequency information of the frequency components, and generate the frequency domain response curve to obtain the inherent frequency response characteristics of the probe (4). Step S4: Change the extension length of the probe (4) by means of the displacement mechanism (5), and repeat steps S1 to S3; obtain the inherent frequency response characteristics of the probe (4) at different extension lengths.

2. The natural frequency testing method as described in claim 1, characterized in that, Before using the laser displacement sensor (6), the laser displacement sensor (6) is calibrated by the dynamic acquisition system (8).

3. The natural frequency testing method as described in claim 1, characterized in that, A Bessel filter is selected to filter and purify the time-domain signal, reducing the interference of current noise from electronic components.

4. The natural frequency testing method as described in claim 1, characterized in that, The initial frequency F0 and the maximum frequency of the acoustic horn (1) encompass the theoretical inherent frequency range of the probe (4).

5. The natural frequency testing method as described in claim 1, characterized in that, The noise excitation of the acoustic horn (1) is single-frequency noise, and the intensity of the single-frequency noise is at least 20dB higher than the intensity of the background noise.

6. The natural frequency testing method as described in claim 1, characterized in that, The laser displacement sensor (6) collects data from the probe (4) under the same frequency single-frequency noise for 30 seconds.

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