An engine tip clearance measuring device based on microwave photon phase discrimination

Abstract

The application discloses an engine tip clearance measuring device based on microwave photon phase discrimination, comprising a mode-locked laser, first and second microwave photon phase discriminators, a voltage-controlled oscillator, a radio frequency power divider, a clearance radio frequency transceiver system and a signal processing unit; the optical pulse signal generated by the mode-locked laser is divided into a reference optical signal and a measuring optical signal; the radio frequency signal output by the voltage-controlled oscillator is divided into two paths, one of which enters the first microwave photon phase discriminator and outputs a first phase error signal for feedback control of the voltage-controlled oscillator, and the other of which enters the clearance radio frequency transceiver system for transmission; the received radio frequency signal enters the second microwave photon phase discriminator, is subjected to phase discrimination processing by using the measuring optical signal, and a clearance measuring signal is obtained; the signal processing unit collects and processes the clearance measuring signal, and obtains a clearance measurement value. The application combines the electrical domain and the optical domain to realize clearance measurement of a microwave signal based on microwave photonics, has small volume, high precision and is not disturbed by an electromagnetic environment.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of engine tip clearance measurement, and particularly relates to an engine tip clearance measurement device based on microwave photon phase discrimination. BACKGROUND

[0002] Tip clearance refers to the gap between the blades of rotating components such as turbines and compressors and their housings or stators. The size of this gap directly affects the aerodynamic performance, efficiency and durability of the engine. Excessive clearance can cause air leakage, reducing engine efficiency; while insufficient clearance can cause the blades to collide with the housing, thereby damaging the blades or housing and affecting the safety and reliability of the engine. With the development of aero-engine technology, especially the emergence of high thrust-to-weight ratio engines, the measurement and optimization of tip clearance have received increasing attention. In the future, more integrated sensor systems and advanced computational models may be used for real-time monitoring and adjustment of tip clearance to achieve optimal engine performance and extend service life.

[0003] In tip clearance measurement, traditional contact measurement is simple and low in cost, but has limited precision and cannot be used for dynamic monitoring; non-contact techniques such as laser and infrared sensors can provide high precision and real-time monitoring, but the equipment is complex and costly; optical measurement has extremely high precision and is suitable for complex geometric analysis, but the equipment is expensive and is greatly affected by environmental interference; magnetic and ultrasonic measurement is suitable for dynamic monitoring, especially in complex environments, but has certain limitations in precision and applicability. SUMMARY

[0004] The purpose of the present application is to provide an engine tip clearance measurement device based on microwave photon phase discrimination, which combines the electrical and optical domains to realize gap measurement of microwave signals based on microwave photonics, has small volume, high precision, and is not affected by electromagnetic environment.

[0005] To achieve the above purpose, the present application provides an engine tip clearance measurement device based on microwave photon phase discrimination, comprising a mode-locked laser, an isolator, a polarization-maintaining beam splitter, a first microwave photon phase discriminator, a second microwave photon phase discriminator, a servo control module, a voltage-controlled oscillator, a radio frequency power divider, a gap radio frequency transceiver system, and a signal acquisition and processing unit.

[0006] The mode-locked laser is used to emit femtosecond laser to generate an optical pulse signal, the isolator is used to protect the mode-locked laser from returning the optical pulse signal to the mode-locked laser, and the polarization-maintaining beam splitter is used to divide the optical pulse signal generated by the mode-locked laser into a reference light signal and a measurement light signal, the reference light signal enters the first microwave photon phase discriminator, and the measurement light signal enters the second microwave photon phase discriminator.

[0007] The voltage-controlled oscillator is used for outputting a radio frequency signal, the radio frequency signal is divided into two paths by a radio frequency power divider, one path enters a first microwave photonic phase discriminator, the first microwave photonic phase discriminator is used for modulating the phase of a reference light signal, and a first phase error signal is outputted, the servo control module is used for feeding back the first phase error signal as a feedback signal to the voltage-controlled oscillator to realize the stability of the output radio frequency signal of the voltage-controlled oscillator, and the other path enters a clearance radio frequency transceiver system, the clearance radio frequency transceiver system is used for transmitting a radio frequency signal and receiving a radio frequency signal reflected by an engine blade tip, the received radio frequency signal enters a second microwave photonic phase discriminator, the second microwave photonic phase discriminator is used for performing phase discrimination processing on the received radio frequency signal by using a measurement light signal, and a second phase error signal is outputted as a clearance measurement signal, and the signal acquisition and processing unit is used for acquiring and processing the clearance measurement signal to obtain a clearance measurement value.

[0008] According to the engine blade tip clearance measurement device based on microwave photonic phase discrimination provided in the embodiment of the present application, the electrical domain and the optical domain are combined to realize the clearance measurement of the microwave signal based on microwave photonics, the device has small volume and high precision, and is not disturbed by the electromagnetic environment. BRIEF DESCRIPTION OF DRAWINGS

[0009] In order to more clearly illustrate the technical solutions of the present application, the drawings used in the description of the embodiments of the present application will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0010] Figure 1 FIG. 1 is a structural schematic diagram of an engine blade tip clearance measurement device based on microwave photonic phase discrimination according to an embodiment of the present application;

[0011] Figure 2 FIG. 2 is a structural schematic diagram of a microwave photonic phase discriminator according to an embodiment of the present application. DETAILED DESCRIPTION

[0012] In order to make the purpose, technical solutions and advantages of the present application more clear, the technical solutions of the present application will be described clearly and completely in combination with the drawings. Obviously, the described embodiments are only some embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the protection scope of the present application.

[0013] An embodiment of the present application provides an engine blade tip clearance measurement device based on microwave photonic phase discrimination, as shown in FIG. 1. Figure 1As shown, the engine tip clearance measurement device of the embodiment of the present application comprises a mode-locked laser 1, an isolator 2, a polarization maintaining beam splitter 3, a delay line 4, a first microwave photonic phase detector 5, a second microwave photonic phase detector 6, a servo control module 7, a voltage-controlled oscillator 8, a radio frequency power divider 9, a clearance radio frequency transceiver system 15, and a signal acquisition and processing unit 14 arranged in sequence on an optical path, wherein the clearance radio frequency transceiver system 15 comprises a radio frequency circulator 10, a radio frequency antenna probe 11, and an automatic gain controller 13. The engine tip clearance measurement device of the embodiment of the present application is used to measure the tip clearance of an aero-engine 12, i.e., the clearance between the tip of the engine and the wall of the engine casing.

[0014] The mode-locked laser 1 emits a femtosecond laser with a wavelength of 1550 nm, which is used to generate an ultra-stable ultra-short pulse laser with a fixed period and a pulse width in the order of femtoseconds. The isolator 2 is used to protect the mode-locked laser 1 from returning the optical signal to the mode-locked laser 1. The polarization maintaining beam splitter 3 divides the optical pulse signal generated by the mode-locked laser 1 into reference light and measurement light.

[0015] The reference light enters the first microwave photonic phase detector 5. The signal of the voltage-controlled oscillator 8 divided by the radio frequency power divider 9 enters the electro-optic phase modulator of the first microwave photonic phase detector 5. At this time, the electro-optic phase modulator controlled by the voltage-controlled oscillator 8 modulates the phase of the reference light signal, and then outputs an error signal using the first microwave photonic phase detector 5. Then, the servo control module 7 phase-locks the error signal to achieve the purpose of stabilizing the radio frequency output signal of the voltage-controlled oscillator 8.

[0016] The measurement light enters the second microwave photonic phase detector 6. The signal of the voltage-controlled oscillator 8 divided by the radio frequency power divider 9 enters the radio frequency circulator 10 of the clearance radio frequency transceiver system 15, and then enters the radio frequency antenna probe 11 through the radio frequency circulator 10 to measure the clearance of the aero-engine 12. Then, the measured clearance signal is input into the automatic gain controller 13 through the radio frequency circulator 10 to control the gain of the radio frequency signal to achieve power stabilization. Finally, the clearance measurement signal is output by the second microwave photonic phase detector 6 by phase modulating the measurement light signal in the electro-optic phase modulator of the second microwave photonic phase detector 6. The clearance measurement value is obtained by collecting and processing the measurement signal through the signal acquisition and processing unit 14.

[0017] The delay line 4 is used to provide time delay for the mode-locked pulse entering the second microwave photonic phase detector 6. During the measurement process, the time delay of the measurement pulse is adjusted so that the measurement of the tip clearance of the aero-engine 12 is in the state of the highest measurement sensitivity.

[0018] The first microwave photonic phase detector 5 and the second microwave photonic phase detector 6 each include a 3×3 coupler, an electro-optic phase modulator, a polarization-maintaining attenuator, and a balanced photodetector. The 3×3 coupler and the electro-optic phase modulator form a Sagnac interference ring, such as... Figure 2 As shown. An electro-optic phase modulator is used to modulate the phase of an optical pulse signal. A 3×3 coupler connects the two output ports of the 3×3 coupler to the optical input and output of the electro-optic phase modulator, forming a stable biased Sagnac interference loop. This enables phase modulation of the periodic optical pulse signal by the microwave radio frequency signal, thereby achieving high-resolution optical microwave frequency phase detection. A polarization-maintaining attenuator is used to balance the power of the optical signal output from the microwave photonic phase detector. A balanced photodetector receives the optical signal output from the microwave photonic phase detector and converts it into an electrical signal.

[0019] The servo control module 7 is used as a feedback signal to control the voltage-controlled oscillator 8 by using the error signal generated by the photoelectric conversion of the signal in the first microwave photonic phase detector 5 as a feedback signal. The voltage-controlled oscillator 8 outputs a radio frequency signal to the radio frequency port of the electro-optic phase modulator to perform phase modulation on the optical signal, and its radio frequency signal frequency is 10 GHz. The radio frequency power divider 9 is used to split the radio frequency signal output by the voltage-controlled oscillator into two paths, one of which is input to the first phase modulator 5, and the other is input to the gap radio frequency transceiver system 15.

[0020] The gap radio frequency transceiver system 15 includes a radio frequency antenna probe 11, a radio frequency looper 10, and an automatic gain controller 13. The radio frequency antenna probe 11 is mounted on the casing wall of the aero-engine and is used to transmit and receive radio frequency signals from the engine blade gap. The radio frequency looper 10 transmits radio frequency signals to the radio frequency antenna probe and receives the radio frequency signals returned by the probe. The automatic gain controller 13 stably inputs the power of the radio frequency signal output from the radio frequency looper 10 into the electro-optic phase modulator of the second microwave photonic phase detector 6. The signal acquisition and processing unit 14 acquires the voltage signal output from the balanced photodetector, calculates and outputs the measured value of the engine blade tip gap.

[0021] The following describes the working principle of the engine blade tip clearance measurement device based on microwave photonic phase detection according to an embodiment of the present invention.

[0022] A mode-locked laser 1 is used as the light source, and a Sagnac interference loop is constructed using a 3×3 coupler and an electro-optic phase modulator. Since the electro-optic phase modulator is a unidirectional phase modulation device, when an optical pulse train is input into the Sagnac loop, the two cyclic pulses experience different phase shifts, which is a function of phase modulation and the intrinsic phase shift of the coupler. Here, the modulation phase... φ Proportional to the phase error Δθ between the position of the optical pulse and the zero-crossing position of the microwave, it can be expressed as:

[0023] (1)

[0024] where V π represents the equivalent voltage amplitude of π phase modulation at the microwave frequency, V RF.amp represents the voltage amplitude of the microwave input.

[0025] The input optical pulse signal can be expressed as

[0026] (2)

[0027] where, is the peak power of the optical pulse, is the duration of the optical pulse, is the period of the optical pulse sequence, and n represents an integer.

[0028] If the microwave signal driving the phase modulator is expressed as

[0029] (3)

[0030] where, is the amplitude of the microwave signal, is the angular frequency of the microwave signal, is the phase difference between the microwave signal and the optical pulse.

[0031] can be expressed as

[0032] (4)

[0033] Then, the output of the Sagnac fiber loop can be expressed as

[0034] (5)

[0035] (6)

[0036] (7)

[0037] where, , , is the output signal of the 3x3 coupler in the Sagnac fiber loop. When the frequency of the microwave source used is an integer multiple of the repetition frequency of the optical pulse sequence (i.e. , M is an integer), and the optical pulse only appears at time, in order to protect the light source from back-reflected light, an optical isolator is inserted at the input port. Therefore , , can be expressed as

[0038] (8)

[0039] (9)

[0040] (10)

[0041] Loss factor α n The constants α and P of an ideal 3×3 coupler are... avg The average power of the optical pulse sequence input to the Sagnac fiber loop satisfies Here, the total optical power (P1+P5+P6) of the interference output is always constant.

[0042] By applying the two outputs of the Sagnac loop to a balanced photodetector (BPD), the error signal Vd can be obtained. The output voltage signal of the BPD can be expressed as follows:

[0043] (11)

[0044] in, and These represent the transconductance gain and responsivity of the BPD, respectively. When the zero-crossing point of the microwave signal is aligned with the optical pulse, the phase difference between them is 0, i.e. At this time, the output voltage of the BPD is 0. When the output of BPD is... The relationship is approximately linear, therefore the expression for Vd can be derived as follows:

[0045] (12)

[0046] Where G is the transimpedance gain, and R is the responsivity of the photodiode in the balanced photodetector. Therefore, the phase detection sensitivity (Kd, [V / rad]) can be expressed as:

[0047] (13)

[0048] From the above formula, it can be seen that the sensitivity of the microwave photonic phase detector is related to the average power of the input optical pulse sequence and the modulation depth of the microwave signal. The phase detection sensitivity is proportional to the input power of the optical pulse sequence and the power of the microwave signal. Therefore, the phase detection sensitivity can be improved by increasing the input power of the optical pulse sequence and the power of the microwave signal. When the phase difference between the microwave signal and the optical pulse is not zero, the output of the BDP is linearly related to the phase difference. When the power of the input optical pulse sequence changes and other factors remain unchanged, it can be seen from formula (13) that the sensitivity is proportional to the average power of the optical pulse.

[0049] Based on the phase detection sensitivity Kd, the radio frequency signal frequency fFor 10GHz, the gap detection sensitivity KL can be obtained as:

[0050] (14)

[0051] Further, the relationship between the error signal (Vd) and the tip clearance (L) is obtained

[0052] (15)

[0053] According to formula (15), the voltage error signal (Vd) output by the BPD can obtain the tip clearance measurement value.

[0054] In the present application, there are four variables, input optical pulse power, sensitivity, BPD output voltage signal and distance, the sensitivity is obtained by measuring the input optical power, and the distance is obtained according to the value of the BPD output voltage.

[0055] The working process of the engine tip clearance measurement device based on microwave photon phase detection in the embodiment of the present application is as follows:

[0056] Step S1: install the radio frequency antenna probe 11 in the mounting hole of the aircraft engine case wall and fix it;

[0057] Step S2: the mode-locked laser 1 outputs a pulse signal with a repetition frequency of f, and the polarization-maintaining beam splitter 3 divides the femtosecond laser into two beams, which enter the first microwave photon phase detector 5 and the second microwave photon phase detector 6 respectively;

[0058] Step S3: the voltage-controlled oscillator 8 with a repetition frequency of n times of the mode-locked laser 1 in step S2 is divided into two paths by the radio frequency power divider 9, one path enters the electro-optic phase modulator in the first microwave photon phase detector 5 to realize phase modulation of the optical signal, outputs a phase error signal, and then the phase error signal enters the balanced photodetector for photoelectric conversion, the converted electrical signal is input into the servo control module 7, and the balance state of the phase error signal is achieved by adjusting the feedback control parameters in the servo control module 7. The other path enters the gap radio frequency transceiver system 15, and the radio frequency loop device 10 in the gap radio frequency transceiver system 15 outputs a radio frequency signal into the second microwave photon phase detector 6 to output a gap measurement signal, and the gap measurement signal is input into the balanced photodetector for photoelectric conversion, and then the electrical signal is input into the signal acquisition and processing unit 14 to obtain the gap measurement value.

[0059] The engine tip clearance measurement device based on microwave photon phase discrimination of the embodiment of the application realizes the optical domain interference of two radio frequency signals through the electro-optic phase modulator in the microwave photon phase discriminator, significantly improves the measurement resolution, uses the gap radio frequency transceiver system to collect the distance information of each turbine blade tip clearance to obtain the measurement value, and the highest measurement accuracy can reach the sub-nanometer level, the application combines the electrical domain and the optical domain to realize the gap measurement of the microwave signal based on the microwave photonics, and has important value for the engine tip clearance measurement application.

[0060] The foregoing merely describes some exemplary embodiments of the present application by way of illustration, and it is needless to say that the described embodiments can be modified in various ways without departing from the spirit and scope of the present application for those skilled in the art. Therefore, the above drawings and descriptions are illustrative in nature and should not be understood as limiting the scope of protection of the claims of the present application.

Claims

1. A device for measuring engine blade tip clearance based on microwave photonic phase detection, characterized in that, It includes a mode-locked laser, isolator, polarization-maintaining beam splitter, first microwave photonic phase detector, second microwave photonic phase detector, servo control module, voltage-controlled oscillator, radio frequency power divider, gap radio frequency transceiver system, and signal acquisition and processing unit. The mode-locked laser is used to emit femtosecond lasers to generate optical pulse signals. The isolator is used to protect the mode-locked laser and prevent the optical pulse signals from returning to the mode-locked laser. The polarization-maintaining beam splitter is used to divide the optical pulse signals generated by the mode-locked laser into a reference optical signal and a measurement optical signal. The reference optical signal enters the first microwave photonic phase detector, and the measurement optical signal enters the second microwave photonic phase detector. The voltage-controlled oscillator (VCO) outputs a radio frequency (RF) signal, which is split into two paths by an RF power divider. One path enters a first microwave photonic phase detector, which modulates the phase of a reference optical signal and outputs a first phase error signal. The servo control module uses the first phase error signal as a feedback signal to control the VCO, thereby stabilizing the output RF signal. The other path enters a gap RF transceiver system, which transmits RF signals and receives RF signals reflected from the engine blade tip. The received RF signal enters a second microwave photonic phase detector, which uses a measurement optical signal to perform phase discrimination on the received RF signal and outputs a second phase error signal as a gap measurement signal. The signal acquisition and processing unit acquires and processes the gap measurement signal to obtain the gap measurement value.

2. The engine blade tip clearance measurement device based on microwave photonic phase detection according to claim 1, characterized in that, The first and second microwave photonic phase detectors each include a coupler, an electro-optic phase modulator, a polarization-maintaining attenuator, and a balanced photodetector. The coupler and the electro-optic phase modulator form a Sagnac interference loop to achieve phase modulation of the periodic optical pulse signal by the microwave radio frequency signal. The polarization-maintaining attenuator is used to adjust the power of the optical signal output from the Sagnac interference loop to a balanced state. The balanced photodetector is used to convert the optical signal output from the polarization-maintaining attenuator into an electrical signal.

3. The engine blade tip clearance measurement device based on microwave photonic phase detection according to claim 2, characterized in that, The electro-optic phase modulator is used to modulate the phase of the optical pulse signal; the coupler is a 3×3 coupler, and the two output ports of the 3×3 coupler are respectively connected to the optical input and output of the electro-optic phase modulator to form a stable biased Sagnac interference loop.

4. The engine blade tip clearance measurement device based on microwave photonic phase detection according to any one of claims 1-3, characterized in that, The gap radio frequency transceiver system includes a radio frequency antenna probe, a radio frequency looper, and an automatic gain controller. The radio frequency antenna probe is mounted on the engine casing wall and is used to send radio frequency signals to the engine blade tip and receive radio frequency signals reflected from the engine blade tip. The radio frequency looper is used to send radio frequency signals to the radio frequency antenna probe and receive radio frequency signals returned by the radio frequency antenna probe. The automatic gain controller is used to input the radio frequency signal output by the radio frequency looper into the second microwave photonic phase detector.

5. The engine blade tip clearance measurement device based on microwave photonic phase detection according to any one of claims 1-3, characterized in that, It also includes a delay line disposed between the polarization-maintaining beam splitter and the second microwave photonic phase detector, the delay line being used to provide a time delay for the measurement optical signal entering the second microwave photonic phase detector.

6. The engine blade tip clearance measurement device based on microwave photonic phase detection according to any one of claims 1-3, characterized in that, The output radio frequency signal frequency of the voltage-controlled oscillator is 10 GHz.

7. The engine blade tip clearance measurement device based on microwave photonic phase detection according to any one of claims 1-3, characterized in that, The mode-locked laser emits a femtosecond laser with a wavelength of 1550nm, generating an ultrastable, ultrashort pulse laser with a fixed period and a pulse width on the femtosecond scale.

8. The engine blade tip clearance measurement device based on microwave photonic phase detection according to claim 3, characterized in that, The signal acquisition and processing unit obtains the clearance measurement value based on the following relationship between the second phase error signal Vd and the tip clearance L: ， ， Kd represents the phase detection sensitivity. f denoted as , where is the frequency of the radio frequency signal, and c is the speed of light.

9. The engine blade tip clearance measurement device based on microwave photonic phase detection according to claim 8, characterized in that, Phase detection sensitivity is expressed as: ， Where α is the loss factor of the 3×3 coupler. and These represent the transconductance gain and responsivity of the balanced photodetector, respectively. Pavg is the average power of the optical pulse sequence input to the Sagnac interference loop. Vπ represents the equivalent voltage amplitude of the π-phase modulation at the applied microwave frequency. VRF.amp represents the voltage amplitude at the microwave input terminal.

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