Frequency domain interferometric tip clearance and fiber bundle tip timing compound sensing system and method

Abstract

The present application discloses a frequency domain interference blade tip clearance and optical fiber bundle type blade tip timing composite sensing system and method, which belongs to the technical field of aero-engine rotor-stator clearance measurement. The system comprises a single-multimode composite optical fiber sensor for detecting reflected light of the end face of the measured blade; a single-mode optical fiber for emitting wide spectrum light and receiving sensing light reflected by the probe end face of the single-multimode composite optical fiber sensor and the end face of the measured blade, and interference forming reflected wide spectrum light; a multimode optical fiber for receiving sensing light reflected by the end face of the measured blade; a frequency domain interference blade tip clearance measurement module for measuring the blade tip clearance; an optical fiber bundle blade tip timing measurement module for measuring the blade tip timing; and a main control module for calculating the position of the measurement point on the measured blade. The method can realize simultaneous measurement of the blade tip clearance and blade vibration, take into account the measurement accuracy of the blade tip clearance and blade tip timing, and also realize accurate positioning of the blade tip clearance measurement result.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of rotor-stator clearance measurement of an aero-engine, and particularly to a frequency domain interference blade tip clearance and a fiber bundle type blade tip timing composite sensing system and method. BACKGROUND

[0002] The moving blade is a core working element of a large rotating machine such as an aero-engine or a gas turbine, and the vibration state and the change of the operation parameter such as the blade tip clearance of the moving blade affect the normal operation and the working efficiency of the whole system.

[0003] The blade tip clearance refers to the distance between the blade tip and the inner wall of the casing, and is closely related to the fuel efficiency, thrust and service life of the engine. The high-precision measurement of the blade tip clearance is of great significance to the blade design, flow field analysis and active clearance control. The blade tip timing, as a non-contact moving blade vibration measurement method, is widely used in the measurement of blade vibration parameters. The basic principle is to install a sensor on the casing to obtain a blade tip sensing signal, measure the time when the blade tip reaches the sensor, and when the blade vibrates, the blade tip reaching time will be advanced or delayed. Combined with the blade speed and the radius of rotation, the blade amplitude can be obtained, and then through various blade tip timing processing algorithms, the blade vibration parameter information can be obtained.

[0004] Real-time monitoring of blade tip clearance and blade vibration is crucial for maintaining equipment operational safety and improving performance. Since both blade tip clearance and blade vibration parameter measurements based on tip timing require non-contact acquisition of blade tip sensing signals, simultaneous measurement is possible. Developing a monitoring method capable of simultaneously measuring tip timing and blade vibration can provide more comprehensive equipment status information while reducing measurement hardware costs and complexity, representing a development trend in blade condition monitoring. Currently, composite sensing methods for blade tip clearance and tip timing can be divided into electrical and optical methods. Electrical methods can be further divided into capacitance methods, eddy current methods, and microwave methods. However, the capacitance and eddy current methods in Chinese patent CN114838671A, "A System and Method for Simultaneous Measurement of Blade Tip Clearance and Blade Tip Arrival Time," suffer from drawbacks such as large sensor size, susceptibility to electromagnetic interference, and measurement results influenced by blade material. Furthermore, these methods can only obtain one clearance value for a single blade, resulting in an equivalent average blade clearance measurement, and cannot measure the clearance at a local or specified point on the blade tip. The microwave method in Chinese patent CN107101600A, "A Microwave-Based Fusion Measurement Device for Blade Tip Clearance and Vibration Parameters," simultaneously measures blade tip clearance and timing by measuring the phase and intensity of microwaves. However, this method is also susceptible to electromagnetic interference, and due to the large divergence angle of the microwave beam, its accuracy and resolution are inferior to the optical method. The optical method in Chinese patent CN113358205A, "A Measurement Device and Method for Synchronously Detecting Blade Vibration and Blade Tip Clearance," uses an optical fiber collimator to transmit and receive laser light, and sinusoidally modulates the laser intensity. It obtains the clearance value using the phase information of the laser light reflected from the blade tip, and then uses the light intensity for blade tip timing. This method uses the same beam of reflected light from the leaf tip to obtain the leaf tip gap and leaf tip timing, which cannot simultaneously ensure the measurement accuracy of both leaf tip gap and leaf tip timing. If single-mode fiber is used to transmit the laser, due to the small core diameter of single-mode fiber, it is impossible to guarantee that there is detectable backlight intensity when the entire leaf tip sweeps across the sensor. The reflected light intensity signal has characteristics of inconsistent width, multiple pulses and strong glitches, resulting in low timing accuracy. If multimode fiber is used to transmit the laser, the mode dispersion of multimode fiber will significantly reduce the measurement accuracy of leaf tip gap.

[0005] Therefore, a composite sensing system and method of frequency domain interferometry blade tip gap and fiber bundle blade tip timing is needed to balance the measurement accuracy of blade tip gap and blade tip timing, and to achieve accurate positioning of blade tip gap measurement results. Summary of the Invention

[0006] The purpose of this invention is to propose a composite sensing system and method for frequency domain interference blade tip gap and fiber bundle blade tip timing.

[0007] A frequency-domain interferometric blade tip gap and fiber bundle blade tip timing composite sensing system includes:

[0008] A single-mode / multimode composite fiber optic sensor is used to detect reflected light from the end face of the blade being tested.

[0009] Single-mode optical fiber is used to emit broadband light and receive the sensing light reflected from the probe end face of the single-mode multimode composite optical fiber sensor and the end face of the blade under test, and the interference forms reflected broadband light.

[0010] Multimode optical fiber is used to receive sensing light reflected from the end face of the blade being tested.

[0011] Frequency domain interferometric blade tip gap measurement module, used to measure blade tip gap based on reflected broadband light in single-mode optical fiber;

[0012] The fiber bundle leaf tip timing measurement module is used to perform leaf tip timing measurement based on the light intensity of the sensing light in the multimode fiber.

[0013] The main control module is used to calculate the position of the measurement point on the blade under test and extract the tip gap of the region of interest based on the measurement results of the frequency domain interferometric tip gap measurement module and the fiber bundle tip timing measurement module.

[0014] Furthermore, the probe structure of the single-mode / multimode composite fiber optic sensor uses a single-mode fiber at its center, and is surrounded by at least one multimode fiber.

[0015] A composite sensing method for frequency-domain interferometric blade tip gap and fiber bundle blade tip timing includes:

[0016] The single-mode fiber emits broadband light and receives the sensing light reflected from the probe end face of the single-mode multimode composite fiber sensor and the end face of the blade under test. The interference forms a reflected broadband light, and the multimode fiber receives the sensing light reflected from the end face of the blade under test.

[0017] Leaf tip gap measurement based on reflected broadband light in single-mode optical fiber;

[0018] Leaf tip timing measurement is performed based on the light intensity of the sensing light in the multimode optical fiber.

[0019] Based on the measurement results, the position of the measurement point on the measured blade is calculated, and the tip gap of the region of interest is extracted.

[0020] Furthermore, the formula for calculating the position of the measurement point on the blade being measured is:

[0021] pos = (ti k -ti r ) / (ti f -ti r );

[0022] Where pos is the position of the measurement point on the blade being measured, and ti k ti represents the measurement time of the k-th gap measurement result on the i-th blade. r For the i-th blade rising edge time, tif is the falling edge time of the i-th blade.

[0023] The present application has the advantages of:

[0024] 1. The present application adopts a single-multimode optical fiber combined sensing probe, which can realize simultaneous measurement of blade tip clearance and blade vibration in a single opening and narrow cabinet environment.

[0025] 2. The present application uses the high-speed and point measurement characteristics of the frequency domain interference clearance measurement module to measure the blade tip clearance of multiple points on a single blade with high precision; the blade tip timing module receives the blade tip timing sensing light through the multimode optical fiber, and since the multimode optical fiber has a large core diameter and a large numerical aperture, the reflected light of the blade can be obtained during the entire blade scanning period, and high-precision measurement of the blade tip timing can be realized, that is, the measurement precision of the blade tip clearance and the blade tip timing can be considered.

[0026] 3. The present application proposes a blade tip clearance point positioning method, which can also realize accurate positioning of the blade tip clearance measurement results for blades with complex blade end shapes, so as to extract the region of interest for analysis. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 is a schematic diagram of the present application frequency domain interference blade tip clearance and fiber bundle type blade tip timing composite sensing system;

[0028] Figure 2 is a radial section view of a single-multimode composite optical fiber sensor fiber bundle;

[0029] Figure 3 is an axial section view of a single-multimode composite optical fiber sensor probe including a single-multimode converter;

[0030] Figure 4 is an axial section view of a single-multimode composite optical fiber sensor probe including an optical lens and a beam splitter;

[0031] Figure 5 is a measured composite sensor multimode fiber bundle and single-mode fiber receiving light intensity and blade tip clearance scatter plot using a single-multimode composite optical fiber sensor probe;

[0032] Figure 6 is a schematic diagram of the algorithm in the main control module. DETAILED DESCRIPTION

[0033] The present application proposes a frequency domain interference blade tip clearance and fiber bundle type blade tip timing composite sensing system and method, which will be further described below in conjunction with the drawings and specific embodiments.

[0034] Figure 1This is a schematic diagram of the composition of the frequency-domain interferometric leaf tip gap and fiber bundle leaf tip timing composite sensing system of the present invention. It includes a main control module, a frequency-domain interferometric leaf tip gap measurement module, a fiber bundle leaf tip timing measurement module, a single-mode fiber, a multi-mode fiber, and a single-mode / multi-mode composite fiber sensor. The single-mode / multi-mode composite fiber sensor is connected to the frequency-domain interferometric leaf tip gap measurement module via a single-mode fiber, and to the fiber bundle leaf tip timing measurement module via a multi-mode fiber. Both the frequency-domain interferometric leaf tip gap measurement module and the fiber bundle leaf tip timing measurement module are connected to the main control module.

[0035] A single-mode / multimode composite fiber optic sensor detects the reflected light from the end face of the blade under test. The single-mode fiber emits broadband light and receives the sensing light reflected from the probe end face of the single-mode / multimode composite fiber optic sensor and the end face of the blade under test, interfering to form reflected broadband light. The multimode fiber receives the sensing light reflected from the end face of the blade under test. The frequency domain interferometric leaf tip gap measurement module measures the leaf tip gap based on the broadband light in the single-mode fiber and the sensing light. The fiber bundle leaf tip timing measurement module measures the leaf tip gap based on the light intensity of the sensing light in the multimode fiber. The main control module calculates the position of the measurement point on the blade under test based on the measurement results of the frequency domain interferometric leaf tip gap measurement module and the fiber bundle leaf tip timing measurement module, and extracts the leaf tip gap of the region of interest.

[0036] Figure 2 This is a radial cross-sectional view of the fiber bundle in a single-mode / multimode composite fiber optic sensor. The sensor consists of one single-mode fiber and N (N≥1) multimode fibers. The fiber arrangement on the cable is such that the single-mode fiber is in the center, with the multimode fibers closely arranged around it. The single-mode fiber emits broadband light and simultaneously receives sensing light reflected from the sensor probe end face and the blade end face; the multimode fiber bundle receives sensing light reflected from the blade end face.

[0037] Figure 3 This is an axial cross-sectional view of a single-mode / multimode composite fiber optic sensor probe, including a single-mode / multimode converter, where the single-mode fiber and the multimode fiber are connected through the single-mode / multimode converter.

[0038] Figure 4 This is an axial cross-sectional view of a single-mode / multimode composite fiber optic sensor probe, including an optical lens and a beam splitter. The optical lens and beam splitter are arranged sequentially from the inside to the outside on the probe end face.

[0039] Tip clearance measurement utilizes sensing light reflected from the sensor probe end face and the blade end face via single-mode optical fiber. The two beams interfere with each other, and the intensity of the interference light can be expressed as:

[0040]

[0041] In the formula Indicates the intensity of the interfering light. Indicates the frequency of the emitted light The original strength at that location, , These are the reflectivities of the sensor and the blade tip, respectively; c represents the speed of light; n represents the refractive index of the medium; and d represents the tip clearance. Interference term. Make the received It appears as periodic oscillating stripes.

[0042] right Perform a Fourier transform (FFT) to obtain the spectrum, and locate the frequency corresponding to the spectral peak, denoted as f. 条纹 ,satisfy:

[0043]

[0044] Therefore, the blade tip clearance measurement result based on the frequency domain interferometry principle is as follows:

[0045]

[0046] Figure 5 To measure the received light intensity and leaf tip gap scatter plot of the multimode fiber bundle and single-mode fiber of the composite fiber sensor probe, a sparse plot was obtained. The received light intensity of the single-mode fiber exhibited characteristics of inconsistent width, multiple pulses, and strong glitches, making it unsuitable for accurate leaf tip timing. In contrast, the light intensity signal received by the multimode fiber bundle was more regular, and the threshold method of the leaf tip timing algorithm could be used to obtain the rising edge time ti of the i-th (i>0 and i is an integer) leaf tip. r and falling edge time ti f The figure also shows a scatter plot of the blade tip gap. Because the frequency domain interferometry method has a high measurement speed for blade tip gap, multiple gap measurement results can be obtained for a single blade.

[0047] Figure 6 This is a schematic diagram of the algorithm within the main control module. Let ti be the measurement time of the k-th gap measurement result on the i-th blade. k The position of the measurement point on the blade can be calculated using the following formula:

[0048] pos = (ti k -ti r ) / (ti f -ti r );

[0049] When pos = 0.5, the tip gap measurement point is located in the middle of the blade; when pos is close to 0 or 1, the tip gap measurement point is located at the edge of the blade. Based on the value of pos, the tip gap of the region of interest can be extracted.

[0050] In summary, the method of the present application adopts a single multimode optical fiber combined sensing probe, which can realize simultaneous measurement of blade tip clearance and blade vibration in a single opening and narrow cabinet environment. The tip clearance sensing light accesses the frequency domain interference clearance measurement module, which utilizes the high speed and point measurement characteristics of the frequency domain interference clearance to perform high precision measurement of multiple points of the blade tip clearance on a single blade. The tip timing sensing light received by the multimode optical fiber accesses the tip timing module, which can obtain blade reflected light during the entire blade scanning period due to the large core diameter and large numerical aperture of the multimode optical fiber, and can realize high precision measurement of the blade tip timing, i.e. the measurement precision of the blade tip clearance and the blade tip timing can be considered. The present application proposes a blade tip clearance point positioning method, which can also realize accurate positioning of the blade tip clearance measurement result for a blade with a complex blade end shape, so as to extract the region of interest for analysis.

Claims

1. A frequency domain interferometric tip clearance and fiber optic bundle tip timing compound sensing system, characterized in that, The application relates to a single-multiple-mode composite optical fiber sensor for detecting reflected light of an end surface of a measured blade, a single-mode optical fiber for emitting wide-spectrum light and receiving reflected sensing light of a probe end surface of the single-multiple-mode composite optical fiber sensor and an end surface of the measured blade, a multiple-mode optical fiber for receiving reflected sensing light of the end surface of the measured blade, a frequency-domain interference blade tip clearance measurement module for measuring a blade tip clearance according to the reflected wide-spectrum light in the single-mode optical fiber, an optical fiber bundle blade tip timing measurement module for measuring a blade tip timing according to light intensity of the sensing light in the multiple-mode optical fiber, and a main control module for calculating a position of a measurement point on the measured blade according to measurement results of the frequency-domain interference blade tip clearance measurement module and the optical fiber bundle blade tip timing measurement module and extracting a blade tip clearance of a point of a region of interest. The probe structure of the single-multiple-mode composite optical fiber sensor is that a single-mode optical fiber is arranged in the center and no less than one multiple-mode optical fiber is arranged around the single-mode optical fiber. The application relates to a single-multiple-mode composite optical fiber sensor for detecting reflected light of an end surface of a measured blade, a single-mode optical fiber for emitting wide-spectrum light and receiving reflected sensing light of a probe end surface of the single-multiple-mode composite optical fiber sensor and an end surface of the measured blade, a multiple-mode optical fiber for receiving reflected sensing light of the end surface of the measured blade, a frequency-domain interference blade tip clearance measurement module for measuring a blade tip clearance according to the reflected wide-spectrum light in the single-mode optical fiber, an optical fiber bundle blade tip timing measurement module for measuring a blade tip timing according to light intensity of the sensing light in the multiple-mode optical fiber, and a main control module for calculating a position of a measurement point on the measured blade according to measurement results of the frequency-domain interference blade tip clearance measurement module and the optical fiber bundle blade tip timing measurement module and extracting a blade tip clearance of a point of a region of interest. The formula for calculating the position of the measurement point on the measured blade is as follows: ​ ​ ​ 2. The frequency-domain interferometric tip clearance and fiber-optic bundle tip timing compound sensing system of claim 1, wherein, ​ 3. The method of frequency domain interferometric tip clearance and fiber-optic bundle tip timing compound sensing, applied to the frequency domain interferometric tip clearance and fiber-optic bundle tip timing compound sensing system according to any one of claims 1-2, characterized in that, ​ ​ ​ ​ ​ 4. The frequency domain interferometric tip clearance and fiber optic bundle tip timing compound sensing method of claim 3, wherein, ​ pos = (ti k -ti r ) / (ti f -ti r ); wherein pos is the position of the measurement point on the measured blade, ti k is the measurement time of the measurement result of the kth gap on the ith blade, r is the rising edge time of the ith blade, f is the falling edge time of the ith blade.

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