Intake passage wall surface pressure measuring device and surge determination method based thereon

Abstract

The application discloses an air inlet channel wall surface pressure measuring device. The device comprises a pressure sensor array arranged in the air inlet channel; the pressure sensor array comprises a group of blind holes arranged on the inner wall of the air inlet channel and arranged along the axial direction of the air inlet channel; the blind holes are divided into an upper space with a larger radial dimension and a lower space with a smaller radial dimension by a step structure arranged on the inner wall of the blind hole; the lower space is sealed by an elastic diaphragm arranged at the bottom of the upper space and an air cavity with a standard atmospheric pressure is formed in the lower space; an optical fiber grating is arranged on the upper surface of the elastic diaphragm; the remaining space in the upper space is filled with the same material as the elastic diaphragm; the optical fiber gratings in the blind holes are sequentially connected through a connecting optical fiber embedded in the inner wall of the air inlet channel and then connected to a demodulation module through the tail of the air inlet channel. The application further discloses a surge determination method based on the air inlet channel wall surface pressure measuring device. The application can realize dynamic high-precision measurement of the flow field of a supersonic air inlet channel.

Description

Technical Field

[0001] This invention relates to the field of aero-engine technology, and in particular to an inlet wall pressure measuring device. Background Technology

[0002] The air intake is a key aerodynamic component of a jet propulsion system. Monitoring the flow field within the air intake ensures its operational stability and provides a reference for design optimization. However, with the rapid development of supersonic flight technology, higher demands are placed on the measurement of the flow field characteristics of supersonic air intakes. Currently, achieving distributed monitoring of changes in the flow field within the air intake without affecting the flow field itself is a pressing technical challenge. The pressure on the air intake wall is a crucial parameter of the flow field. Traditional piezoresistive Kulite and piezoelectric PCB sensors require openings within the air intake to draw out airflow, resulting in some loss of flow field data. Furthermore, their large area limits high spatial resolution pressure detection. In addition, electrical sensors require expensive shielding cables.

[0003] To address the shortcomings of traditional electrical sensors, researchers have proposed using fiber optic grating sensors for dynamic pressure measurement of the inlet flow field. However, existing techniques for measuring flow fields using fiber optic gratings suffer from limitations in their packaging, resulting in low range and sensitivity of the sensors, making it difficult to capture real-time flow field changes. Furthermore, their protection mechanisms can cause shear stress in the sensor, compromising operational stability. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide an air intake wall pressure measuring device, which is based on a distributed fiber optic grating sensor with a special packaging method, and can realize dynamic high-precision measurement of the supersonic air intake flow field, and has the advantages of high temperature resistance, electromagnetic interference resistance, and no flow field interference.

[0005] The present invention specifically adopts the following technical solutions to solve the above-mentioned technical problems: An air intake duct wall pressure measuring device includes a pressure sensor array disposed in the air intake duct and a demodulation module disposed outside the air intake duct. The pressure sensor array includes a set of blind holes disposed on the inner wall of the air intake duct and arranged along the axial direction of the air intake duct. The blind holes are divided into an upper space with a larger radial dimension and a lower space with a smaller radial dimension by a stepped structure disposed on the inner wall of the blind holes. The lower space is sealed by an elastic diaphragm installed at the bottom of the upper space, forming an air cavity with a standard atmospheric pressure therein. A fiber optic grating is laid on the upper surface of the elastic diaphragm. The remaining space in the upper space is filled with the same material as the elastic diaphragm. The fiber optic gratings in each blind hole are sequentially connected by connecting optical fibers embedded in the inner wall of the air intake duct and then connected to the demodulation module through the tail of the air intake duct.

[0006] Preferably, the connecting optical fibers are the same continuous optical fiber, and the fiber grating is fabricated on the continuous optical fiber.

[0007] Furthermore, a fixing ring adapted to the stepped structure is also installed in the blind hole for fixing the elastic diaphragm.

[0008] Preferably, the surfaces of the fiber grating and the connecting optical fiber are coated with a polyimide protective layer.

[0009] Preferably, the fiber grating is laid at the center of the upper surface of the elastic diaphragm.

[0010] Preferably, the elastic diaphragm is made of silicone.

[0011] Furthermore, the intake duct wall pressure measuring device also includes an optical fiber protection structure disposed at the tail of the intake duct. The optical fiber protection structure includes a groove formed on the intake duct wall from the first position at the tail of the intake duct to the intake duct outlet. A silicone transition surface is laid inside the groove between the first position at the tail of the intake duct and the second position at the tail of the intake duct. A semi-circular plastic sleeve is disposed in the groove between the second position at the tail of the intake duct and the intake duct outlet. The distance from the first position at the tail of the intake duct to the intake duct outlet is greater than the distance from the second position at the tail of the intake duct to the intake duct outlet.

[0012] Preferably, the outer surface of the filling material in the upper space of the blind hole is polished to a smooth surface flush with the inner wall surface of the air intake.

[0013] The surge determination method based on the intake wall pressure measuring device described in any of the above technical solutions includes the following steps: Step 1: Determine whether there is a jump in the pressure signal collected by each fiber Bragg grating. If so, determine that the shock wave is located in the air intake and the air intake is not in a surge state; otherwise, proceed to step 2. Step 2: Take the pressure signal collected by any fiber Bragg grating and determine whether its amplitude is in an upward state. If so, proceed to step 3; otherwise, determine that the air intake is not in a surge state. Step 3: Analyze the spectrum of the pressure signal collected by any fiber optic grating. If the slope of the line connecting at least two maxima of the spectrum amplitude to 0 exceeds the preset value, it is determined that the air intake is in a surge state; otherwise, it is determined that the air intake is not in a surge state.

[0014] Preferably, the fiber grating selected in step 2 and / or step 3 is the fiber grating closest to the air intake outlet.

[0015] Compared with the prior art, the technical solution of the present invention has the following beneficial effects: This invention addresses the challenge of dynamic flow field measurement in air intakes by innovatively improving the packaging method of distributed fiber Bragg grating sensors. A set of blind holes with a stepped structure are opened on the inner wall of the air intake. The fiber Bragg grating is laid on the upper surface of an elastic diaphragm that forms an air cavity marked with atmospheric pressure. The blind holes are filled with the same material as the elastic diaphragm. Under the combined action of the elastic diaphragm, the air cavity, and the airflow inside the air intake, the pressure measurement accuracy and range of the fiber Bragg grating are greatly improved, which is sufficient to meet the requirements of dynamic flow field measurement in hypersonic air intakes, and will not cause distortion of the air intake flow field. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of a specific embodiment of the intake duct wall pressure measuring device of the present invention; Figure 2 This is an exploded view of the fiber Bragg grating packaging structure in a specific embodiment; Figure 3 This is a flowchart illustrating the surge determination method of the present invention; Figure 4 This is a comparison chart of the measurement results of the fiber optic pressure sensor of this invention and a traditional pressure sensor; Figure 5 This is a pressure distribution diagram obtained by the intake wall pressure measuring device of the present invention under different throttling ratios; Figure 6 This is a schematic diagram showing the amplitude variation of a single pressure sensor signal. Figure 7 This is a spectrum of a single pressure sensor signal under different throttling ratios.

[0017] Figure 1 and Figure 2 The following figure labels are included: 1. Air intake duct, 2. Fiber Bragg grating pressure sensor, 3. Fiber optic protection structure, 4. Nylon sleeve, 5. Fiber Bragg grating string, 6. Filler, 7. Fixing ring, 8. Fiber Bragg grating, 9. Elastic diaphragm, 10. Blind hole. Detailed Implementation

[0018] To address the challenge of dynamic measurement of the airflow field in the intake, this invention proposes an improved packaging method for the distributed fiber Bragg grating sensor. A set of blind holes with a stepped structure are created on the inner wall of the intake. The fiber Bragg grating is then laid on the upper surface of an elastic diaphragm forming a standard atmospheric pressure air cavity. The blind holes are filled with the same material as the elastic diaphragm. Through the combined action of the elastic diaphragm, the air cavity, and the airflow inside the intake, the pressure measurement accuracy and range of the fiber Bragg grating are significantly improved, sufficient to meet the dynamic measurement requirements of the hypersonic intake flow field without causing distortion of the intake flow field.

[0019] The intake duct wall pressure measuring device proposed in this invention includes a pressure sensor array disposed in the intake duct and a demodulation module disposed outside the intake duct. The pressure sensor array includes a set of blind holes disposed on the inner wall of the intake duct and arranged along the intake duct axis. The blind holes are divided into an upper space with a larger radial dimension and a lower space with a smaller radial dimension by a stepped structure disposed on the inner wall of the blind holes. The lower space is sealed by an elastic diaphragm installed at the bottom of the upper space, forming an air cavity with a standard atmospheric pressure. A fiber optic grating is laid on the upper surface of the elastic diaphragm. The remaining space in the upper space is filled with the same material as the elastic diaphragm. The fiber optic gratings in each blind hole are sequentially connected by connecting optical fibers embedded in the inner wall of the intake duct and then connected to the demodulation module through the tail of the intake duct.

[0020] Preferably, the connecting optical fibers are the same continuous optical fiber, and the fiber grating is fabricated on the continuous optical fiber.

[0021] Furthermore, a fixing ring adapted to the stepped structure is also installed in the blind hole for fixing the elastic diaphragm.

[0022] Preferably, the surfaces of the fiber grating and the connecting optical fiber are coated with a polyimide protective layer.

[0023] Preferably, the fiber grating is laid at the center of the upper surface of the elastic diaphragm.

[0024] Preferably, the elastic diaphragm is made of silicone.

[0025] Furthermore, the intake duct wall pressure measuring device also includes an optical fiber protection structure disposed at the tail of the intake duct. The optical fiber protection structure includes a groove formed on the intake duct wall from the first position at the tail of the intake duct to the intake duct outlet. A silicone transition surface is laid inside the groove between the first position at the tail of the intake duct and the second position at the tail of the intake duct. A semi-circular plastic sleeve is disposed in the groove between the second position at the tail of the intake duct and the intake duct outlet. The distance from the first position at the tail of the intake duct to the intake duct outlet is greater than the distance from the second position at the tail of the intake duct to the intake duct outlet.

[0026] Preferably, the outer surface of the filling material in the upper space of the blind hole is polished to a smooth surface flush with the inner wall surface of the air intake.

[0027] To facilitate public understanding, the technical solution of the present invention will be described in detail below through a specific embodiment and in conjunction with the accompanying drawings: The intake duct wall pressure measuring device in this embodiment is as follows: Figure 1As shown, a set of fiber Bragg grating pressure sensors 2 are sequentially embedded along the axial direction of the air intake duct 1 on the lower inner wall. Each fiber Bragg grating pressure sensor 2 is connected sequentially to form a fiber Bragg grating string 5 via connecting optical fibers embedded in the inner wall of the air intake duct. This string is then connected to a demodulation module (not shown in the figure) at the tail end of the air intake duct 1. To prevent the fiber Bragg grating string 5 from being affected by shear stress, an optical fiber protection structure 3 is provided at the tail end of the air intake duct 1, such as... Figure 1 As shown, the fiber optic protection structure 3 includes a groove formed on the wall of the air intake duct 1 from the first position at the tail end of the air intake duct (10cm from the air intake outlet in this embodiment) to the air intake outlet. A silicone transition surface is laid inside the groove between the first position at the tail end of the air intake duct (10cm from the air intake outlet in this embodiment) and the second position at the tail end of the air intake duct (5cm from the air intake outlet in this embodiment). A semi-circular plastic sleeve is provided in the groove between the second position at the tail end of the air intake duct (5cm from the air intake outlet in this embodiment) and the air intake outlet. To further improve the protection of the tail fiber, in this embodiment, the fiber optic cables after the second position at the tail end of the air intake duct (5cm from the air intake outlet in this embodiment) are all inserted into the nylon sleeve 4. Through the multiple protections of the fiber optic protection structure 3 and the nylon sleeve 4, the tail fiber of the fiber optic grating string 5 can avoid damage caused by shear stress, which would lead to a decrease in measurement performance. The connecting optical fibers between each fiber Bragg grating are embedded in grooves pre-drilled on the inner wall surface of the air intake, and epoxy resin is used to fill the grooves into which the connecting optical fibers are embedded.

[0028] To further improve system stability and reduce the number of required leads and the impact of electromagnetic interference, the fiber grating string 5 in this embodiment uses the same optical fiber to process the fiber gratings at various locations using a femtosecond laser and then coats them with a polyimide protective layer. Its mechanical strength is higher than that of ordinary solutions, and its operating temperature range is -200℃ to 300℃, making it more suitable for extreme working environments such as the air intake.

[0029] The structure of the fiber optic pressure sensor 2 in this embodiment is as follows: Figure 2As shown, the device includes a blind hole 10 disposed on the inner wall of the air intake duct. The blind hole 10 is divided into an upper space with a larger radial dimension and a lower space with a smaller radial dimension by a stepped structure disposed on the inner wall of the blind hole. In this embodiment, the height of the stepped structure from the bottom of the blind hole is 5 mm, and the lateral width of the stepped structure is 1 mm. The blind hole 10 is divided into upper and lower parts by the stepped structure. The upper space is a circular hole with a diameter of 10 mm and a depth of 1 mm, and the lower space is a concentric blind hole with a diameter of 8 mm and a depth of 5 mm. An elastic diaphragm 9 with a diameter of 10 mm and a thickness of 0.3 mm is fixed on the stepped structure, and the elastic diaphragm 9 seals the lower space. An air cavity with a standard atmospheric pressure is formed within it; then, a fiber optic grating 8 is laid on the upper surface of the elastic diaphragm; to prevent the fiber optic grating 8 from shifting during installation, in this embodiment, the elastic diaphragm 9 and the fiber optic grating 8 are fixed by a fixing ring 7 with a thickness of 0.7 mm, an outer diameter of 10 mm, and an inner diameter of 8 mm, and then the remaining space of the blind hole 10 is filled with a filler 6 of the same material as the elastic diaphragm 9; to prevent unevenness after filling, which would cause distortion of the airflow field in the intake duct, the outer surface of the filler 6 is also polished in this embodiment to form a smooth surface flush with the inner wall surface of the intake duct. In order to maximize the pressure sensitivity of the sensor, according to the principle of small deflection, the pressure influence on the diaphragm is greatest at the center of the elastic diaphragm (i.e., the center of the blind hole), therefore, in this embodiment, the fiber optic grating 8 is laid at this location.

[0030] In this embodiment, a silicone material with a low Young's modulus is selected to make the elastic diaphragm 9 and the filler 6.

[0031] When the air pressure in the intake duct changes, the pressure difference between it and the air cavity below the blind hole 10 changes accordingly, causing the elastic diaphragm 9 to deform. This, in turn, causes a corresponding drift in the center wavelength of the fiber Bragg grating 8. The demodulation module demodulates the wavelength drift signal to obtain the intake duct wall pressure at the corresponding location. Wavelength demodulation of the fiber Bragg grating sensor is a mature existing technology, and will not be elaborated here for the sake of brevity.

[0032] Because the fiber Bragg grating pressure sensor adopts the above-mentioned special packaging structure and protection measures, its pressure measurement accuracy, range and reliability are significantly better than those of existing fiber Bragg grating sensors.

[0033] Due to the high precision and large range of the intake duct wall pressure measuring device of this invention, the intake duct surge condition can be quickly and easily determined directly based on the obtained measurement signals. The surge determination method is as follows: Figure 3 As shown, the specific steps include: Step 1: Determine whether there is a jump in the pressure signal collected by each fiber Bragg grating. If so, determine that the shock wave is located in the air intake and the air intake is not in a surge state; otherwise, proceed to step 2. Step 2: Take the pressure signal collected by any fiber Bragg grating and determine whether its amplitude is in an upward state. If so, proceed to step 3; otherwise, determine that the air intake is not in a surge state. Step 3: Analyze the spectrum of the pressure signal collected by any fiber optic grating. If the slope of the line connecting at least two maxima of the spectrum amplitude to 0 exceeds the preset value, it is determined that the air intake is in a surge state; otherwise, it is determined that the air intake is not in a surge state.

[0034] In step 2 and / or step 3, the fiber Bragg grating selected can be any one of them. Considering that the pressure signal collected by the fiber Bragg grating closest to the air intake outlet has the largest change amplitude, it is preferred to use the pressure signal collected by this fiber Bragg grating for the judgment in step 2 and / or step 3.

[0035] To verify the effectiveness of the technical solution of this invention, the following verification experiments were conducted: A binary external pressure supersonic inlet was selected as the benchmark inlet model for the experiment, and a supersonic wind tunnel test at Mach 2 was conducted. Based on the model's measurement requirements, a ten-point fiber Bragg grating string with a polyimide coating, etched by a femtosecond laser, was chosen. Each sensing grating on this fiber Bragg grating string is spaced 10 mm apart. The fiber Bragg gratings were encapsulated using the aforementioned encapsulation scheme according to their positions, and the fiber Bragg grating string was protected using the aforementioned protective measures. Finally, the optical fiber was led out of the wind tunnel and connected to the demodulator and the host computer.

[0036] When the wind tunnel is turned on, supersonic airflow enters the inlet, causing changes in wall pressure and creating a pressure difference between the airflow and the air cavity below the blind hole. This results in a corresponding drift in the center wavelength of the fiber optic grating. The wavelength signal is transmitted to a demodulator, which converts the optical signal into an electrical signal and inputs it to a host computer. The host computer then converts this electrical signal into a pressure signal, thus enabling pressure measurement. A comparison of the pressure measured by this invention with the signal measured by a traditional dynamic pressure sensor is provided. Figure 4 As shown, the signal trend measured by the measurement system of the present invention is very similar to that of the traditional dynamic pressure sensor, and it is also less affected by noise interference, which verifies the system's ability to measure the pressure on the intake wall.

[0037] After the pressure signal is measured, further analysis is performed to determine whether the air intake is in a surge state. First, the pressures measured by the measurement system under various clogging conditions (simulating different flight states of an aircraft) are compared. Figure 5The figures show the pressure measured by the measurement system at different locations when the throttling ratio is 0%, 10%, 30%, 45%, 60%, 70%, and 80%. At a throttling ratio of 0%, with the wind tunnel not yet open, the pressure measured by all sensors is approximately 4 kPa. After opening the wind tunnel and increasing the throttling ratio to 10%, the pressures of all sensors generally increase. However, adjacent sensors do not show a significant pressure difference, indicating that at this throttling ratio, the shock wave has not yet reached the measurement area. When the throttling ratio reaches 30%, the pressure measured by the gratings at positions P09 and P10 is significantly higher than when the throttling ratio is 20%, indicating that the shock wave is between P08 and P09, affecting the sensors at positions P09 and P10. When the throttling ratio reaches 45%, the impact of the end-of-line impact on the inlet intensifies, and the shock wave is between P02 and P03, leading to an increase in the pressure measured by the sensors at positions P03 to P10. Once the throttling ratio exceeds 60%, all sensors will be affected, indicating that the shock wave is outside the intake and may cause surge.

[0038] Once it is determined that the shock wave is outside the air intake, its signal needs further analysis. The signal is sampled in chronological order, with a total of three samplings, each with 1000 sampling points, for amplitude analysis. First, all the maxima and minima of the sampled signal are taken, and the difference between the average of the maxima and the average of the minima is calculated and used as the signal amplitude. Figure 6 The three sets of signals were sampled sequentially over time. The amplitude of the first sampled signal was approximately 1.2, the amplitude of the subsequent sampled signal was approximately 2.5, and the amplitude of the last sampled signal was approximately 6.1. The amplitude showed a gradual upward trend over time, indicating that surge may be occurring, and we proceed to the next step of the assessment.

[0039] The frequency spectrum of the above three sampled signals after time-frequency transformation is obtained by applying Fourier transform to the above sampled signals, as shown below. Figure 7 As shown. Find the two maxima of the spectral amplitude in these sampled signals and calculate the slope of the line connecting these two points to the zero point. If the slope of the line connecting the two maxima of the first sampled signal to the zero point is less than 0.001, then the air intake is not in a surge state. If the slope of the line connecting the two maxima of the next two sampled signals to the zero point is greater than 0.001, then the air intake is determined to be in a surge state.

Claims

1. An intake duct wall pressure measuring device, comprising a pressure sensor array disposed in the intake duct, and a demodulation module disposed outside the intake duct; characterized in that, The pressure sensor array includes a set of blind holes disposed on the inner wall of the air intake and arranged along the axial direction of the air intake. The blind holes are divided into an upper space with a larger radial dimension and a lower space with a smaller radial dimension by a stepped structure disposed on the inner wall of the blind holes. The lower space is sealed by an elastic diaphragm installed at the bottom of the upper space, forming an air cavity with a standard atmospheric pressure. A fiber grating is laid on the upper surface of the elastic diaphragm. The remaining space in the upper space is filled with the same material as the elastic diaphragm. The fiber gratings in each blind hole are connected sequentially by connecting optical fibers embedded in the inner wall of the air intake and then connected to the demodulation module through the tail of the air intake.

2. The intake duct wall pressure measuring device as described in claim 1, characterized in that, The connecting optical fibers are the same continuous optical fibers, and the fiber grating is fabricated on this continuous optical fiber.

3. The intake duct wall pressure measuring device as described in claim 1, characterized in that, A fixing ring adapted to the stepped structure is also installed in the blind hole for fixing the elastic diaphragm.

4. The intake duct wall pressure measuring device as described in claim 1, characterized in that, The surfaces of the fiber grating and the connecting optical fibers are coated with a polyimide protective layer.

5. The intake duct wall pressure measuring device as described in claim 1, characterized in that, The fiber grating is laid at the center of the upper surface of the elastic diaphragm.

6. The intake duct wall pressure measuring device as described in claim 1, characterized in that, The elastic diaphragm is made of silicone.

7. The intake duct wall pressure measuring device as described in claim 1, characterized in that, It also includes a fiber optic protection structure disposed at the tail of the air intake duct. The fiber optic protection structure includes a groove formed on the air intake duct wall from a first position at the tail of the air intake duct to the air intake duct outlet. A silicone transition surface is laid inside the groove between the first position at the tail of the air intake duct and a second position at the tail of the air intake duct. A semi-circular plastic sleeve is disposed in the groove between the second position at the tail of the air intake duct and the air intake outlet. The distance from the first position at the tail of the air intake duct to the air intake outlet is greater than the distance from the second position at the tail of the air intake duct to the air intake outlet.

8. The intake duct wall pressure measuring device as described in claim 1, characterized in that, The outer surface of the filling material in the upper space of the blind hole is polished to a smooth surface flush with the inner wall surface of the air intake.

9. A surge determination method based on the intake duct wall pressure measuring device as described in any one of claims 1 to 8, characterized in that, Includes the following steps: Step 1: Determine whether there is a jump in the pressure signal collected by each fiber Bragg grating. If so, determine that the shock wave is located in the air intake and the air intake is not in a surge state; otherwise, proceed to step 2. Step 2: Take the pressure signal collected by any fiber Bragg grating and determine whether its amplitude is in an upward state. If so, proceed to step 3; otherwise, determine that the air intake is not in a surge state. Step 3: Analyze the spectrum of the pressure signal collected by any fiber optic grating. If the slope of the line connecting at least two maxima of the spectrum amplitude to 0 exceeds the preset value, it is determined that the air intake is in a surge state. Otherwise, it is determined that the air intake is not in a surge state.

10. The surge determination method as described in claim 9, characterized in that, The fiber Bragg grating selected in step 2 and / or step 3 is the fiber Bragg grating closest to the air intake outlet.

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