Blade tip timing method and device based on laser Doppler effect

Abstract

The invention discloses a blade tip timing method and device based on a laser Doppler effect, which are used for realizing optical fiber blade tip timing. The method comprises the following steps: S1, emitting laser, and dividing the laser into a first light beam and a second light beam through an optical fiber beam splitter; s2, irradiating the first light beam to a blade tip through a temperature-resistant optical fiber probe, receiving laser reflected by the blade tip, forming signal light participating in interference, and sending the signal light to an optical fiber beam combiner; s3, sending the second light beam to an optical fiber beam combiner to form reference light participating in interference; s4, performing interference on the signal light and the reference light to form an interference light field, and acquiring an electric signal of the interference light field; step S5, obtaining blade tip time ti according to the electric signal; the invention further discloses a blade tip timing device based on the laser Doppler effect, and the blade tip time of the blade tip of the engine blade in the casing of the engine is measured. The method has the advantages of accurate measurement and high engineering applicability.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optical precision measurement, in particular to a blade tip timing method and device based on laser Doppler effect. BACKGROUND

[0002] Blades are one of the core parts of an aero-engine, which will be in an extreme high-temperature, high-pressure, heavy load and other complex environment during work, and will vibrate under the joint action of centrifugal force, aerodynamic force and the like. Vibration overrun and fatigue failure caused by vibration will cause serious engine failure. Therefore, accurate measurement of blade vibration parameters (amplitude, frequency) is one of the important means for engine condition monitoring, fault diagnosis and accident prevention, and non-contact blade tip timing technology is the most effective method to realize vibration parameter measurement.

[0003] In order to realize the measurement of fan, compressor and turbine blade vibration parameters of the engine, the blade vibration parameter measurement method based on the blade tip timing principle is currently mainly used, and the traditional blade tip timing method mainly includes fiber optic blade tip timing method, capacitance blade tip timing method and microwave blade tip timing method. Among them, the fiber optic blade tip timing method has been widely used in engineering experiments and is the mainstream blade vibration parameter measurement method at present. The fiber optic blade tip timing method is to emit continuous laser to the blade, and when the blade reaches, the reflected light intensity reaches a certain set trigger threshold, so as to determine the time when the blade tip reaches. However, the reflected light intensity is closely related to the distance between the fiber optic sensor and the blade tip, the reflectivity of the blade tip and the light emission of the combustion products. However, in the actual engineering environment, due to the change of blade tip gap, the change of optical reflection characteristics of blade tip under high temperature condition and the light emission under high temperature radiation and other factors, the reflected light intensity has a sharp random fluctuation, and the timing accuracy is generally only in the order of microseconds, which cannot effectively distinguish the relatively small blade vibration amplitude and high-order vibration mode. SUMMARY

[0004] The present application aims to provide a blade tip timing method and device based on laser Doppler effect, which has the advantages of accurate measurement and high engineering applicability.

[0005] In order to achieve the above-mentioned purpose, the present application provides a blade tip timing method based on laser Doppler effect, which is used to realize fiber optic blade tip timing. The method comprises the following steps: step S1, emitting laser, passing through the fiber optic beam splitter and dividing the laser into first light beam and second light beam; step S2, irradiating the first light beam to the blade tip through the temperature-resistant fiber optic probe, receiving the laser reflected by the blade tip, forming signal light participating in interference, and sending to the fiber optic beam combiner; step S3, sending the second light beam to the fiber optic beam combiner to form reference light participating in interference; step S4, signal light and reference light interfere to form interference light field, and the electrical signal of the interference light field is acquired ; step S5, acquiring the electrical signal The tip time ti is obtained.

[0006] Preferably, in the step S1, the emitted laser is split into two beams by the fiber beam splitter, the first beam has a light field form and the second beam has a light field form respectively.

[0007]

[0008]

[0009] k = 2π / λ

[0010] f0=c / λ

[0011] wherein, is the amplitude of the laser; k is the wave vector of the laser; λ is the wavelength of the laser; r0 is the initial propagation path of the laser; f0 is the frequency of the laser; c is the speed of light; t is time; η is a constant determined by the splitting ratio of the fiber beam splitter.

[0012] Preferably, the step S2 comprises: a step S21, the first beam is irradiated onto the tip of the blade by the temperature-resistant fiber probe, and the expression of the light field of the first beam emitted by the temperature-resistant fiber probe is .

[0013]

[0014] wherein, α is the collection efficiency of the temperature-resistant fiber probe; ρ is the reflectivity of the light field of the tip of the blade; η1 is the amplitude attenuation factor of the first beam in reaching the temperature-resistant fiber probe link; r 10 is the laser propagation path from the fiber beam splitter to the temperature-resistant fiber probe; f1 is the laser with Doppler frequency shift reflected from the tip of the blade received by the temperature-resistant fiber probe;

[0015] A step S22, the temperature-resistant fiber probe receives the laser reflected by the tip of the blade, transmits to the fiber combiner after passing through the fiber amplifier to form the signal light participating in interference, and the expression of the light field of the signal light participating in interference is .

[0016]

[0017] wherein, η2 is the amplitude attenuation factor of the connection port from the temperature-resistant fiber probe to the fiber amplifier; K is the amplitude amplification factor of the fiber amplifier; r 20 is the laser propagation path from the temperature-resistant fiber probe to the fiber combiner.

[0018] Preferably, in the step S22, the f1 is:

[0019]

[0020] wherein ω is the rotation speed of the engine to which the blade belongs; R is the radius of the blade; θ is the angle between the central axis of the temperature-resistant optical fiber probe installation and the normal line of the blade rotor.

[0021] Preferably, in the step S3, the expression of the reference light field participating in the interference is .

[0022]

[0023] wherein r 30 is the laser propagation path of the second light beam from the optical fiber beam splitter to the optical fiber combiner; is the amplitude attenuation factor of the laser propagation path of the second light beam from the optical fiber beam splitter to the optical fiber combiner.

[0024] Preferably, the step S4 comprises: a step S41, the signal light and the reference light are interfered to obtain an interference light field, and the light intensity of the interference light field is .

[0025]

[0026]

[0027]

[0028] = r 30 - r 10 - r 20

[0029] wherein A is the amplitude of the signal light; B is the amplitude of the reference light; is the phase difference caused by the signal light and the reference light participating in the interference after experiencing different paths;

[0030] a step S42, according to the light intensity after the interference, an electric signal is obtained by a photoelectric detector.

[0031]

[0032] wherein k is the sensitivity of the photoelectric detector.

[0033] Preferably, the step S5 comprises: a step S51, detecting whether the electric signal at the T time point satisfies that the high-frequency component of the electric signal is If yes, output the current time as the tip time ti; if no, let T=T+T, and return to step S51.

[0034] A tip timing device based on laser Doppler effect, the device is used to realize the tip timing method based on laser Doppler effect; the tip time of the tip of the engine blade in the engine casing is measured; the device comprises: a fiber laser emitting laser with a wavelength of lambda; a fiber beam splitter connected with the fiber laser, which divides the input laser into first and second beams for output in equal proportion; a fiber loop, comprising: a first port, a second port and a third port; wherein the light beam unidirectionally passes from the first port to the second port, and the light beam unidirectionally passes from the second port to the third port; the first port is connected with the fiber beam splitter; a transmission optical fiber connected with the second port, used for transmitting the first light beam to the position to be tested; a temperature-resistant optical fiber probe fixedly arranged outside the engine casing, the temperature-resistant optical fiber probe is installed on the engine casing; a fiber amplifier connected with the third port, which amplifies the reflected light reflected from the tip of the engine blade; a fiber combiner connected with the fiber amplifier and the fiber beam splitter respectively, which receives the second light beam as reference light, and interferes the reference light with the signal light to form an interference light field; a collection module connected with the fiber combiner, which analyzes the interference light field to obtain the tip time.

[0035] Preferably, the collection module comprises: a photoelectric converter connected with the fiber combiner, which converts the light intensity of the interference light field into an electrical signal; a collection card connected with the photoelectric converter, which collects the electrical signal in real time and carries out time-frequency analysis to extract the feature frequency occurrence time information; a computer connected with the collection card, which analyzes and stores the feature frequency occurrence time information output by the collection card, i.e.

[0036] Compared with the prior art, the tip timing method and device based on laser Doppler effect provided by the application have the following beneficial effects:

[0037] Firstly, the tip timing method and device based on laser Doppler effect proposed by the application irradiate the detection laser to the high-speed rotating blade through the optical fiber sensor, and due to the optical Doppler effect, the reflected laser will have a Doppler shift; the reflected light of the blade is heterodyne interfered with the reference laser, and the frequency mutation time of the interference signal is measured to realize the accurate measurement of the tip arrival time.

[0038] Secondly, the application provides a blade tip timing method and device based on laser Doppler effect, which can avoid the influence of intensity fluctuation in engineering environment by measuring the blade arrival time in frequency domain, and the measurement precision of blade tip arrival time can reach nanosecond level, so the application has high engineering applicability. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1 The application provides a blade tip timing device based on laser Doppler effect.

[0040] Fig. 2 (a) is a test result of laser interference method.

[0041] Fig. 2 (b) is a test result of light intensity reflection.

[0042] Figure 3 The application provides a flowchart of the blade tip timing method based on laser Doppler effect.

[0043] Reference signs:

[0044] 1-fiber laser, 2-fiber beam splitter, 3-fiber ring, 4-transmission fiber, 5-temperature-resistant fiber probe, 6-fiber amplifier, 7-fiber beam combiner, 8-optoelectronic converter, 9-acquisition card, 10-computer, 11-engine case, 12-engine blade, 31-first port, 32-second port, 33-third port. DETAILED DESCRIPTION

[0045] The application will be described in detail below with reference to the accompanying drawings of the embodiments of the application. Figure 1 The application Figure 3 The technical solutions, structural features, achieved purposes and effects of the embodiments of the application will be described in detail.

[0046] It should be noted that the drawings are greatly simplified and use non-precise proportions, only for the purpose of conveniently and clearly assisting in the description of the embodiments of the application, and are not used to limit the application, so they do not have technical significance, any modification of structure, change of proportion relationship or adjustment of size, as long as it does not affect the effects and purposes of the application, should still fall within the scope of the disclosed technology.

[0047] It should be noted that, in the present invention, relational terms such as first and second, etc. are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus comprising a series of elements includes not only the elements explicitly listed, but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus.

[0048] like Figure 3 As shown, the present invention proposes a blade tip timing method and device based on the laser Doppler effect, which is used to achieve fiber blade tip timing; the method includes:

[0049] Step S1, emitting laser light, passing through an optical fiber beam splitter and splitting the laser light into a first beam and a second beam;

[0050] Step S2: irradiate the first light beam onto the blade tip through a temperature-resistant optical fiber probe, receive the laser reflected by the blade tip, form a signal light participating in interference, and send it to the optical fiber combiner;

[0051] Step S3, sending the second light beam to the fiber combiner to form a reference light participating in interference;

[0052] Step S4: The signal light and the reference light interfere with each other to form an interference light field, and the electrical signal of the interference light field is obtained. ;

[0053] Step S5: According to the electrical signal Get the tip time ti.

[0054] Specifically, in step S1, the laser light emitted by the fiber laser is first divided into two beams by a fiber beam splitter. The light field form of the first beam is With the second beam light field form They are:

[0055]

[0056]

[0057] k=2π / λ

[0058] f0=c / λ

[0059] in, is the amplitude of the laser; k is the laser wave vector; λ is the wavelength of the laser; r0 is the initial propagation path of the laser; f0 is the frequency of the laser; c is the speed of light; t is the time; η is a constant determined by the fractional ratio of the optical fiber splitter.

[0060] Specifically, the step S2 comprises:

[0061] Step S21, the first light beam is irradiated to the blade tip through the temperature-resistant optical fiber probe, the light field expression of the first light beam emitted by the temperature-resistant optical fiber probe is For,

[0062]

[0063] Wherein, α is the collection efficiency of the temperature-resistant optical fiber probe; ρ is the light field reflectivity of the blade tip; η1 is the amplitude attenuation factor of the first light beam reaching the temperature-resistant optical fiber probe link; r 10 The laser propagation path from the optical fiber beam splitter to the temperature-resistant optical fiber probe; f1 is the laser with Doppler frequency shift reflected from the blade tip and received by the temperature-resistant optical fiber probe;

[0064] In the preferred embodiment, the f1 is

[0065]

[0066] Wherein, ω is the rotating speed of the engine to which the blade belongs; R is the radius of the blade, and θ is the included angle between the installation center axis of the temperature-resistant optical fiber probe and the normal line of the blade rotor.

[0067] Step S22, the temperature-resistant optical fiber probe receives the laser reflected by the blade tip, transmits to the optical fiber combiner through the optical fiber amplifier, forms the signal light participating in interference, and the expression of the light field of the signal light participating in interference is For,

[0068]

[0069] Wherein, η2 is the amplitude attenuation factor of the connecting port of the temperature-resistant optical fiber probe to the optical fiber amplifier (specifically, the connecting port of the optical fiber ring to the optical fiber amplifier); K is the amplitude amplification factor of the optical fiber amplifier; r 20 The laser propagation path from the temperature-resistant optical fiber probe to the optical fiber combiner;

[0070] In addition, when the engine rotates, the blade tip leaves the field of view of the temperature-resistant optical fiber probe, the temperature-resistant optical fiber probe will not receive the laser reflected from the blade tip, ρ=0, which represents such a case.

[0071] Specifically, in the step S3, the expression of the light field of the reference light participating in interference is For,

[0072]

[0073] Wherein, r 30 The laser propagation path from the optical fiber beam splitter to the optical fiber combiner; an amplitude attenuation factor for a laser propagation path of the second light beam from the fiber beam splitter to the fiber combiner;

[0074] Specifically, the step S4 comprises:

[0075] Step S41, the signal light and the reference light interfere to obtain an interference light field, the light intensity of the interference light field is for:

[0076]

[0077]

[0078]

[0079] = r 30 - r 10 - r 20

[0080] wherein A is the amplitude of the signal light, B is the amplitude of the reference light, is the phase difference caused by the signal light and the reference light after experiencing different paths.

[0081] Step S42, according to the light intensity after interference, an electrical signal is obtained by a photoelectric detector ;

[0082]

[0083] wherein k is the sensitivity of the photoelectric detector.

[0084] Specifically, the step S5 comprises:

[0085] Step S51, whether the electrical signal at the T time point satisfies that the high-frequency component of the electrical signal is ;

[0086] Step S52, if satisfied, output the current time as the blade tip time ti; if not satisfied, let T=T+T, and return to step S51.

[0087] The principle here is as follows, the first two terms of the electrical signal are the direct current components generated by the interference of the signal light and the reference light; the third term , the AC component generated by the interference; when the blade tip passes through the field of view of the temperature-resistant fiber probe, the temperature-resistant fiber probe will receive the reflected light of the blade tip, and then the above-described interference signal. When the blade tip leaves the field of view of the temperature-resistant fiber probe, the temperature-resistant fiber probe will not receive any reflected light, so when only the second term , that is, only the DC component of the reference light.

[0088] Therefore, in specific embodiments, the electric signal i output by the photoelectric detector can be collected in real time by a capture card, and time-frequency analysis is performed. When the blade tip does not appear in the field of view of the temperature-resistant fiber probe, it is known that it only has a DC component, and no high-frequency component appears in the frequency spectrum.

[0089] When the blade tip enters the field of view of the temperature-resistant fiber probe, it is known that it contains an AC component, and a high-frequency component will appear in the frequency spectrum, so the frequency of the high-frequency component is:

[0090]

[0091] When the capture card detects the appearance of the high-frequency component fi, the appearance time of the high-frequency signal is recorded as the blade tip time ti, which represents the arrival time of the blade tip to the field of view of the temperature-resistant fiber probe, that is, the blade tip timing is realized. The arrival time information can be used for analysis of the vibration amplitude and vibration frequency of the blade.

[0092] In addition, as Figure 1 shown, the present application also provides a heterodyne interference type blade tip timing device based on laser Doppler effect; the blade tip time of the blade tip of the engine blade 12 in the engine casing 11 is measured; the device comprises:

[0093] a fiber laser 1 emitting laser with a wavelength of λ;

[0094] a fiber beam splitter 2 connected with the fiber laser 1, which divides the input laser into two equal output beams, i.e., the first light beam and the second light beam;

[0095] a fiber circulator 3, which comprises a first port 31, a second port 32 and a third port 33; wherein the light beam passes from the first port 31 to the second port 32 in one direction, and the light beam passes from the second port 32 to the third port 33 in one direction; the first port 31 is connected with the fiber beam splitter 2;

[0096] a transmission optical fiber 4 connected with the second port 32, used for transmitting the first light beam to the position to be tested;

[0097] The temperature-resistant optical fiber probe 5 is fixedly arranged outside the engine case 11; the first light beam is irradiated onto the blade tip of the engine blade 12 through the temperature-resistant optical fiber probe 5, and the reflected light of the blade tip is received; subsequently, the reflected light will be amplified by the subsequent optical fiber amplifier 6 and will be used as the interference signal light; the temperature-resistant optical fiber probe 5 is arranged on the engine case 11 at a certain angle (θ with the normal line);

[0098] The optical fiber amplifier 6 is connected with the third port 33, and the reflected light (weak laser) reflected from the engine blade tip is power-amplified;

[0099] The optical fiber combiner 7 is connected with the optical fiber amplifier 6 and the optical fiber beam splitter 2 respectively, receives the second light beam as the reference light, and performs interference between the reference light and the signal light to form an interference light field; in the embodiment, the combiner ratio is 50:50, and the reference light and the signal light are combined (i.e., the interference light field is formed) after the combination.

[0100] The acquisition module is connected with the optical fiber combiner 7, analyzes the interference light field, and obtains the blade tip time.

[0101] Specifically, the acquisition module comprises:

[0102] The photoelectric converter 8 is connected with the optical fiber combiner 7, and converts the light intensity of the interference light field into an electrical signal;

[0103] The acquisition card 9 is connected with the photoelectric converter 8, collects the electrical signal in real time, and carries out time-frequency analysis to extract the characteristic frequency occurrence time information;

[0104] The computer 10 is connected with the acquisition card 9, analyzes and stores the characteristic frequency occurrence time information output by the acquisition card 9, that is, the blade tip arrival time sequence.

[0105] For the heterodyne interference blade tip timing system based on the laser Doppler effect, the best embodiment is illustrated by taking the structure shown in FIG. 1 as an example. Figure 1 The laser light source used in the figure is a 1550nm continuous laser, which is connected to the input port of the 1×2 optical fiber beam splitter 2, and the splitting ratio is 90:10; the output port of the 1×2 optical fiber beam splitter 2 is connected with the first port 31 of the optical fiber ring 3, the second port 32 of the optical fiber ring 3 is connected with the transmission optical fiber 4, the transmission optical fiber 4 is connected with the temperature-resistant optical fiber probe 5, and the temperature-resistant optical fiber probe 5 is arranged on the engine case 11 at an angle θ of 3° with the normal line.

[0106] The engine blade 12 operates at a maximum of 8000 revolutions per minute. The third port 33 of the optical fiber circulator 3 is connected with the input port of the optical fiber amplifier 6, the reflected signal light is amplified to 20 mW, and then is connected with the input port of the 2x1 optical fiber combiner 7. The other output port of the 1x2 optical fiber splitter 2 is connected with the input port of the 2x1 optical fiber combiner, the output port of the 2x1 optical fiber combiner 7 is connected with the optical input port of the photoelectric converter 8 with a bandwidth of 1 GHz, the electrical output port of the photoelectric converter 8 is connected with the acquisition card 9, the acquisition card 9 completes real-time acquisition and then carries out short-time Fourier transform processing, the blade tip arrival time is obtained through high-frequency signal appearance time judgment, and is uploaded to a computer, and the blade vibration amplitude is obtained through calculation.

[0107] As shown in FIG. 2 (a) and FIG. 2 (b). This is the final effect presentation, the blade time measurement is calculated through the same algorithm after the blade vibration amplitude, and then comparison can be seen, the method can realize clear identification of 6 to 13 times frequency vibration, and the commercial technology can only measure 6 to 10 times frequency vibration, and the improvement of the discrimination ability is caused by the improvement of the blade timing accuracy.

[0108] The heterodyne interference type blade tip timing method based on the laser Doppler effect provided by the application, compared with the traditional light intensity reflection type method, since the blade tip timing accuracy is greatly improved, the amplitude resolution obtained by calculation is obviously enhanced, the problem that the timing accuracy of the traditional optical fiber blade tip timing technology is greatly affected by factors such as light intensity of the blade tip, blade tip-casing gap change and the like is solved, and a new technical method is provided for effective measurement of micro blade vibration amplitude and high-order vibration mode.

[0109] Although the content of the application has been described in detail through the above preferred embodiments, it should be recognized that the above description should not be considered as limitation of the application. After reading the above content, various modifications and substitutions of the application will be obvious to those skilled in the art. Therefore, the protection scope of the application should be limited by the appended claims.

Claims

1. A blade tip timing method based on the laser Doppler effect, used to achieve fiber blade tip timing; characterized in that: The method comprises: Step S1, emitting laser light, passing through an optical fiber beam splitter and splitting the laser light into a first beam and a second beam; Step S2: irradiate the first light beam onto the blade tip through a temperature-resistant optical fiber probe, receive the laser reflected by the blade tip, form a signal light participating in interference, and send it to the optical fiber combiner; Step S3, sending the second light beam to the fiber combiner to form a reference light participating in interference; Step S4: The signal light and the reference light interfere with each other to form an interference light field, and the electrical signal of the interference light field is obtained. ; Step S5: According to the electrical signal Get the tip time ti.

2. The blade tip timing method based on the laser Doppler effect according to claim 1, characterized in that: In step S1, the emitted laser is divided into two beams by a fiber optic beam splitter. The light field form of the first beam is With the second beam light field form They are: k=2π / λ f0=c / λ in, is the amplitude of the laser; k is the laser wave vector; λ is the wavelength of the laser; r0 is the initial propagation path of the laser; f0 is the frequency of the laser; c is the speed of light; t is the time; η is a constant determined by the fractional ratio of the optical fiber splitter.

3. The blade tip timing method based on the laser Doppler effect according to claim 2, characterized in that: The step S2 comprises: Step S21: irradiate the first light beam onto the blade tip through a heat-resistant fiber optic probe. The expression of the light field of the first light beam emitted by the heat-resistant fiber optic probe is: for, Wherein, α is the collection efficiency of the temperature-resistant optical fiber probe; ρ is the light field reflectivity of the blade tip; η1 is the amplitude attenuation factor of the first light beam when it reaches the temperature-resistant optical fiber probe link; r 10 is the laser propagation path from the optical fiber beam splitter to the temperature-resistant optical fiber probe; f1 is the laser with Doppler frequency shift reflected from the blade tip and received by the temperature-resistant optical fiber probe; In step S22, the heat-resistant optical fiber probe receives the laser reflected from the blade tip, transmits it to the optical fiber combiner after passing through the optical fiber amplifier, and forms the signal light participating in the interference. The expression of the signal light field participating in the interference is: for: Wherein, η2 is the amplitude attenuation factor of the connection port between the temperature-resistant optical fiber probe and the optical fiber amplifier; K is the amplitude amplification factor of the optical fiber amplifier; r 20 This is the laser propagation path from the temperature-resistant fiber optic probe to the fiber optic combiner.

4. The blade tip timing method based on the laser Doppler effect according to claim 3, characterized in that: In step S22, f1 is: Where ω is the rotational speed of the engine to which the blade belongs; R is the radius of the blade; and θ is the angle between the central axis of the temperature-resistant optical fiber probe and the normal of the blade rotor.

5. The blade tip timing method based on the laser Doppler effect according to claim 4, characterized in that: In step S3, the expression of the reference light field participating in the interference is for: Among them, r 30 is the laser propagation path of the second light beam from the optical fiber splitter to the optical fiber combiner; is the amplitude attenuation factor of the second light beam in the laser propagation path from the fiber splitter to the fiber combiner.

6. The blade tip timing method based on the laser Doppler effect according to claim 5, characterized in that: The step S4 comprises: Step S41: The signal light interferes with the reference light to obtain an interference light field. The light intensity of the interference light field is for: = r 30 - r 10 - r 20 Where A is the amplitude of the signal light; B is the amplitude of the reference light; It is the phase difference caused by the signal light and reference light participating in the interference after they have gone through different paths; Step S42, according to the light intensity after interference , obtain electrical signals through photodetectors ; Where k is the sensitivity of the photodetector.

7. The blade tip timing method based on the laser Doppler effect according to claim 6, characterized in that: The step S5 comprises: Step S51: Detect the electrical signal at time point T , whether it meets the electrical signal The high frequency component of ; Step S52: If satisfied, output the current time as the blade tip time ti; if not satisfied, set T=T+T and return to step S51.

8. A blade tip timing device based on the laser Doppler effect, characterized in that: The device is used to implement a blade tip timing method based on the laser Doppler effect as described in any one of claims 1 to 7; The tip time of the blade tip of an engine blade (12) in an engine casing (11) is measured; the device comprises: A fiber laser (1) emitting laser light having a wavelength of λ; A fiber beam splitter (2) is connected to the fiber laser (1) and divides the input laser into a first light beam and a second light beam in equal proportion for output; An optical fiber circulator (3), the optical fiber circulator (3) comprising: a first port (31), a second port (32), and a third port (33); wherein a light beam passes from the first port (31) to the second port (32) in one direction, and a light beam passes from the second port (32) to the third port (33) in one direction; the first port (31) is connected to a fiber optic beam splitter (2); A transmission optical fiber (4), connected to the second port (32), for transmitting the first light beam to a location to be tested; A heat-resistant optical fiber probe (5) is fixedly arranged outside the engine casing (11), and the heat-resistant optical fiber probe (5) is installed on the engine casing (11); an optical fiber amplifier (6) connected to the third port (33) for amplifying the power of the reflected light reflected from the engine blade tip; The optical fiber combiner (7) is connected to the optical fiber amplifier (6) and the optical fiber splitter (2), receives the second light beam as reference light, and interferes the reference light with the signal light to form an interference light field; The acquisition module is connected to the optical fiber combiner (7) to analyze the interference light field and obtain the blade tip time.

9. The blade tip timing device based on the laser Doppler effect according to claim 8, characterized in that: The acquisition module includes: A photoelectric converter (8) is connected to the optical fiber combiner (7) to convert the light intensity of the interference light field into an electrical signal; An acquisition card (9) is connected to the photoelectric converter (8) to acquire the electrical signal in real time, and to perform time-frequency analysis to extract information on the time when the characteristic frequency occurs; The computer (10) is connected to the acquisition card (9) and analyzes and stores the characteristic frequency occurrence time information output by the acquisition card (9).

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