High-speed dynamic total temperature measurement system and method based on fiber grating combination

Abstract

The application discloses a high-speed dynamic total temperature measuring system and method based on a fiber grating combination, and the system comprises a fiber grating high-frequency response total temperature probe, a fiber grating high-speed demodulation system and an upper computer; the method steps are as follows: 1) high-speed airflow is stagnated at the end of the fiber grating high-frequency response total temperature probe, heat is transferred to fiber gratings I and II, thereby generating fiber grating spectrum signals I and II carrying temperature information; 2) the fiber grating high-speed demodulation system converts the fiber grating spectrum signals I and II carrying temperature information into electrical signals I and II carrying temperature information, and transmits the electrical signals I and II to the upper computer; 3) the upper computer performs temperature calculation on the electrical signals I and II carrying temperature information, and obtains the airflow total temperature. The application provides a dynamic airflow total temperature measuring system, the transmission signal of the system is an optical signal and is not affected by electromagnetic interference, and the stability of the measurement result is better.

Description

Technical Field

[0001] This invention relates to the field of total temperature measurement technology, specifically a high-speed dynamic total temperature measurement system and method based on fiber optic gratings. Background Technology

[0002] In the aerospace field, the study of transient mechanisms is essential. For example, during the start-up, acceleration, and failure processes of aero-engines, especially in the event of sudden turbine shaft failure, the transient time can be on the order of milliseconds. Understanding the transient evolution mechanisms of engines plays a crucial role in the design of advanced engines and ensuring aircraft safety.

[0003] Fluid temperature is a crucial indicator in transient evolution mechanisms. While steady-state testing is relatively mature, transient testing remains a challenge. When the temperature of the measured airflow changes rapidly, a temperature sensor needs to respond quickly to ensure accurate real-time measurement. However, temperature sensors inherently possess thermal inertia and cannot immediately reflect changes in airflow temperature.

[0004] Thermocouples are commonly used temperature sensors in fluid temperature testing, characterized by their simple structure, high accuracy, and strong reliability. While thermocouples provide accurate measurements of steady-state temperatures, their transient temperature measurements lag behind changes in fluid temperature due to thermal inertia. Currently, there are two types of fast-response thermocouples: wire thermocouples and composite thermocouples. Wire thermocouples with a wire diameter of approximately 0.08 mm can achieve response times as fast as tens of milliseconds, but due to their small diameter, they are easily damaged during use. Composite thermocouples, although maintaining mechanical strength to some extent, still suffer from inherent drawbacks such as lower thermoelectric potential and thermoelectric potential rate, lower sensitivity, susceptibility to burnout, and susceptibility to electromagnetic interference.

[0005] Fiber Bragg gratings (FBGs) are increasingly being used for high-speed airflow temperature measurement due to their advantages such as small size, immunity to electromagnetic interference, high sensitivity, and no need for insulation treatment. A common approach is to first fabricate a single FBG into a total temperature probe, then dynamically calibrate the probe's characteristics and perform dynamic compensation during measurement to obtain the true temperature of the measured airflow. However, the size of FBGs cannot be infinitely reduced; otherwise, fabrication would be extremely difficult, and they would still be susceptible to damage under high-speed airflow conditions. Therefore, improving the dynamic temperature measurement response speed while ensuring structural strength is a key issue that needs to be addressed to expand their application in high-speed airflow total temperature testing. Summary of the Invention

[0006] The purpose of this invention is to provide a high-speed dynamic total temperature measurement system based on fiber Bragg grating (FBG) assembly, including a FBG high-frequency response total temperature probe, a FBG high-speed demodulation system, and a host computer.

[0007] The fiber grating high-frequency response total temperature probe includes fiber grating I, fiber grating II, transmission fiber I, and transmission fiber II;

[0008] The fiber grating I and fiber grating II monitor airflow temperature information and transmit the fiber grating spectral signal I and fiber grating spectral signal II carrying temperature information to the fiber grating high-speed demodulation system through transmission fiber I and transmission fiber II, respectively.

[0009] The fiber grating high-frequency response total temperature probe also includes a dual-hole support tube;

[0010] The end of the transmission optical fiber I is engraved with a fiber grating I;

[0011] One end of the transmission optical fiber I, on which the fiber grating I is inscribed, is inserted into one hole of the double-hole support tube.

[0012] The transmission optical fiber I and transmission optical fiber II are made of the same material but have different diameters;

[0013] The end of the transmission optical fiber II is engraved with fiber grating II;

[0014] One end of the transmission optical fiber II, on which the fiber grating II is inscribed, is inserted into the other hole of the double-hole support tube.

[0015] The transmission optical fiber I is placed in one hole of the dual-hole support tube, and the transmission optical fiber II is placed in the other hole.

[0016] The fiber grating high-frequency response total temperature probe also includes a high-temperature adhesive;

[0017] The high-temperature adhesive is filled between the double-hole support tube and transmission optical fiber I and transmission optical fiber II;

[0018] The high-temperature adhesive forms a high-temperature adhesive bead at one end of the double-hole support tube.

[0019] The transmission fiber I and transmission fiber II include single-mode fiber multi-core armored optical cables.

[0020] The fiber Bragg grating high-speed demodulation system converts fiber Bragg grating spectral signal I and fiber Bragg grating spectral signal II carrying temperature information into electrical signal I and electrical signal II carrying temperature information, and transmits them to the host computer.

[0021] The fiber Bragg grating high-speed demodulation system has multiple signal channels, thereby enabling high-speed parallel processing of several fiber Bragg grating spectral signals.

[0022] The host computer performs temperature calculations on electrical signals I and II, which carry temperature information, to obtain the total airflow temperature.

[0023] The host computer (4) is used to control the operation of the fiber optic grating high-speed demodulation system.

[0024] Total airflow temperature Satisfy the following formula:

[0025] (1)

[0026] In the formula, These represent the volumes of fiber grating I and the airflow convection heat transfer section, and the volumes of fiber grating II and the airflow convection heat transfer section, respectively. These represent the areas of fiber grating I and the airflow convection heat transfer section, respectively; For fiber optic gratings in The center wavelength of the reflection spectrum at time; , These represent the rates of change of the center wavelengths of fiber grating I and fiber grating II over time at the measured moments, respectively. , These represent the temperature sensitivity coefficients of fiber Bragg grating I and fiber Bragg grating II, respectively. , These represent the intercepts of the temperature-wavelength curves for fiber Bragg grating I and fiber Bragg grating II, respectively. These represent the diameters of fiber Bragg grating I and fiber Bragg grating II, respectively.

[0027] The fabrication steps of the fiber Bragg grating high-frequency response total temperature probe are as follows:

[0028] 1) Write fiber Bragg grating I at the end of transmission fiber I; write fiber Bragg grating II at the end of transmission fiber II;

[0029] 2) Determine and mark the relative positions of the double-hole support tube, transmission fiber I, and transmission fiber II on the precision displacement stage.

[0030] 3) Apply high-temperature adhesive to the marked areas of transmission fiber I and transmission fiber II;

[0031] 4) Insert one end of the transmission fiber I with fiber grating I engraved on it into one hole of the double-hole support tube, and insert one end of the transmission fiber II with fiber grating II engraved on it into the other hole of the double-hole support tube.

[0032] 5) Curing the high-temperature adhesive in a high-temperature oven to form a high-temperature adhesive bead at one end of the double-hole support tube.

[0033] The method for using a high-speed dynamic total temperature measurement system based on fiber Bragg gratings includes the following steps:

[0034] 1) Insert the fiber Bragg grating high-frequency response total temperature probe into the flow field to be measured, so that fiber Bragg grating I and fiber Bragg grating II are facing the direction of the high-speed airflow;

[0035] 2) The high-speed airflow stops at the end of the fiber grating high-frequency response total temperature probe, and the kinetic energy is converted into internal energy. Through heat transfer, the heat is transferred to fiber grating I and fiber grating II, so that fiber grating I and fiber grating II generate fiber grating spectral signal I and fiber grating spectral signal II carrying temperature information, respectively. The fiber grating spectral signal I and fiber grating spectral signal II carrying temperature information are then transmitted to the fiber grating high-speed demodulation system through transmission fiber I and transmission fiber II, respectively.

[0036] 3) The fiber Bragg grating high-speed demodulation system converts the fiber Bragg grating spectral signal I and fiber Bragg grating spectral signal II carrying temperature information into electrical signal I and electrical signal II carrying temperature information, and transmits them to the host computer;

[0037] The fiber Bragg grating high-speed demodulation system uses edge filtering to demodulate the fiber Bragg grating spectral signal I and fiber Bragg grating spectral signal II, which carry temperature information.

[0038] 4) The host computer performs temperature calculations on electrical signals I and II carrying temperature information to obtain the total airflow temperature. The steps include:

[0039] 4.1) Establish the thermal conductivity differential equation for the fiber grating, namely:

[0040] (2)

[0041] In the formula, denoted as ρ, where c is the density of the fiber Bragg grating material; ρ is the specific heat of the fiber Bragg grating material; V is the volume of the section where the fiber Bragg grating exchanges heat with the airflow; F is the area of ​​the section where the fiber Bragg grating exchanges heat with the airflow; and h is the convective heat transfer coefficient between the fiber Bragg grating and the airflow. This refers to the internal temperature of the fiber grating. The airflow temperature;

[0042] 4.2) The host computer reconstructs the temperature information carried by electrical signals I and II at time τ, obtaining:

[0043] (3)

[0044] (4)

[0045] In the formula, for The actual temperature of the airflow at any given moment; for The temperature information carried by electrical signal I and electrical signal II at any given moment; c1 and c2 are the densities of fiber grating I (101) and fiber grating II (102); c1 and c2 are the specific heats of fiber grating I (101) and fiber grating II (102); h1 and h2 are the convective heat transfer coefficients between fiber grating I (101) and fiber grating II (102) and the airflow; F1 and F2 are the areas of the convective heat transfer portions between fiber grating I (101) and fiber grating II (102) and the airflow; V1 and V2 are the volumes of the convective heat transfer portions between fiber grating I (101) and fiber grating II (102) and the airflow.

[0046] 4.3) Introducing aerodynamic parameters Substituting this into formula (4), we get:

[0047] (5)

[0048] (6)

[0049] In the formula, D is the diameter of the fiber grating;

[0050] 4.4) Ratio formulas (5) and (6) and substitute them into the fiber grating temperature-wavelength formula to obtain the total airflow temperature. ,Right now:

[0051] (7)

[0052] In the formula, These represent the volumes of fiber grating I and the airflow convection heat transfer section, respectively.

[0053] The technical effects of this invention are undeniable. This invention proposes a high-frequency response airflow total temperature probe and its manufacturing method. The probe uses a combined fiber optic grating as the temperature sensing element, transmits signals through optical fiber, and greatly reduces the volume of the total temperature probe. Two fiber optic gratings of the same material but different diameters measure the temperature of the airflow at the same location, and the measurement results can be compensated in real time, thereby improving the response time of the dynamic airflow total temperature probe.

[0054] This invention proposes a dynamic airflow total temperature measurement system based on a combined fiber Bragg grating high-frequency response airflow total temperature probe. The transmission signal of this system is an optical signal, which is not subject to electromagnetic interference, and the measurement results are more stable.

[0055] The system employs a high-speed fiber Bragg grating demodulator combined with a fast and high-precision fiber Bragg grating demodulation algorithm to ensure real-time demodulation of the fiber Bragg grating center wavelength and improve system measurement time.

[0056] This invention proposes a dynamic airflow total temperature measurement method. This method uses two fiber gratings of different diameters to measure the airflow temperature at the same point, which can eliminate the convective heat transfer coefficient characteristics in the fiber grating heat conduction differential equation, and achieve the effect that the system response time is less than the response time of a single fiber grating. Attached Figure Description

[0057] Figure 1 This is a high-speed airflow total temperature measurement system based on a combined fiber Bragg grating;

[0058] Figure 2 This is a structural diagram of a high-frequency response total temperature probe based on a combined fiber Bragg grating.

[0059] Figure 3 Schematic diagram of fiber Bragg grating temperature measurement principle;

[0060] Figure 4 Simulation results for improving system response time by combining fiber Bragg gratings;

[0061] Figure 5 This is a flowchart of the combined fiber optic grating temperature measurement method of the present invention;

[0062] Figure 6 This is a schematic diagram of the combined fiber optic grating high-speed airflow total temperature measurement system of the present invention used for temperature measurement in the internal flow channel of an aero-engine.

[0063] Figure 7 Flowchart for fabricating a high-frequency response total temperature probe based on a combined fiber Bragg grating;

[0064] Figure 8 This is a system structure diagram of the edge-filtered fiber Bragg grating fast demodulation method;

[0065] Figure 9 Schematic diagram of the fast demodulation method for edge-filtered fiber Bragg gratings;

[0066] In the figure: 1. Fiber Bragg grating high-frequency response total temperature probe; 2. Fiber Bragg grating high-speed demodulation system; 3. Host computer; 4. Fiber Bragg grating I101; 5. Fiber Bragg grating II102; 6. Transmission fiber I103; 7. Transmission fiber II104; 8. Dual-hole support tube; 9. High-temperature adhesive; 100. High-temperature adhesive beads. Detailed Implementation

[0067] The present invention will be further described below with reference to embodiments, but it should not be construed that the scope of the present invention is limited to the following embodiments. Various substitutions and modifications made based on ordinary technical knowledge and common practices in the art without departing from the above-described technical concept of the present invention should be included within the scope of protection of the present invention.

[0068] Example 1:

[0069] See Figures 1 to 9A high-speed dynamic total temperature measurement system based on fiber Bragg gratings includes a fiber Bragg grating high-frequency response total temperature probe 1, a fiber Bragg grating high-speed demodulation system 2, and a host computer 3.

[0070] The fiber grating high-frequency response total temperature probe 1 includes fiber grating I101, fiber grating II102, transmission fiber I103, and transmission fiber II104;

[0071] The fiber gratings I101 and II102 monitor airflow temperature information and transmit the fiber grating spectral signal I and fiber grating spectral signal II carrying temperature information to the fiber grating high-speed demodulation system 2 through transmission fiber I103 and transmission fiber II104, respectively.

[0072] The fiber grating high-frequency response total temperature probe 1 also includes a dual-hole support tube 105;

[0073] The end of the transmission optical fiber I103 is engraved with a fiber grating I101;

[0074] One end of the transmission optical fiber I103, on which the fiber grating I101 is engraved, is inserted into one hole of the double-hole support tube 105.

[0075] The transmission optical fiber I103 and the transmission optical fiber II104 are made of the same material but have different diameters;

[0076] The end of the transmission optical fiber II104 is engraved with a fiber grating II102;

[0077] One end of the transmission optical fiber II104, on which the fiber grating II102 is inscribed, is inserted into the other hole of the double-hole support tube 105.

[0078] The dual-hole support tube 105 has a transmission optical fiber I103 placed in one hole and a transmission optical fiber II104 placed in the other hole.

[0079] The fiber grating high-frequency response total temperature probe 1 also includes high-temperature adhesive 106;

[0080] The high-temperature adhesive 106 is filled between the double-hole support tube 105 and the transmission optical fiber I103 and transmission optical fiber II104.

[0081] The high-temperature adhesive forms a high-temperature adhesive bead 107 at one end of the double-hole support tube 105.

[0082] The transmission optical fiber I103 and transmission optical fiber II104 include single-mode fiber multi-core armored optical cables.

[0083] The fiber Bragg grating high-speed demodulation system 2 converts the fiber Bragg grating spectral signal I and fiber Bragg grating spectral signal II carrying temperature information into electrical signal I and electrical signal II carrying temperature information, and transmits them to the host computer 3.

[0084] The fiber Bragg grating high-speed demodulation system has multiple signal channels, thereby enabling high-speed parallel processing of several fiber Bragg grating spectral signals.

[0085] The host computer 3 performs temperature calculations on electrical signals I and II carrying temperature information to obtain the total airflow temperature.

[0086] The host computer 3 is used to control the operation of the fiber Bragg grating high-speed demodulation system 2.

[0087] Total airflow temperature Satisfy the following formula:

[0088] (1)

[0089] In the formula, These represent the volumes of fiber grating I101 and the airflow convection heat transfer section, and the volumes of fiber grating II102 and the airflow convection heat transfer section, respectively. These represent the areas of fiber grating I101 and the airflow convection heat transfer section, and the areas of fiber grating II102 and the airflow convection heat transfer section, respectively. For fiber optic gratings in The center wavelength of the reflection spectrum at time; , These represent the rates of change of the center wavelengths of fiber gratings I101 and II102 over time at the measured moments, respectively. , These represent the temperature sensitivity coefficients of fiber grating I101 and fiber grating II102, respectively. , These represent the intercepts of the temperature-wavelength curves for fiber gratings I101 and II102, respectively. The diameters of fiber grating I101 and fiber grating II102 are given.

[0090] The fabrication steps of the fiber Bragg grating high-frequency response total temperature probe 1 are as follows:

[0091] 1) Write fiber Bragg grating I101 at the end of transmission fiber I103; write fiber Bragg grating II102 at the end of transmission fiber II104;

[0092] 2) Determine and mark the relative positions of the double-hole support tube 105, transmission fiber I103 and transmission fiber II104 on the precision displacement stage.

[0093] 3) Apply high-temperature adhesive to the marked areas on transmission optical fibers I103 and II104;

[0094] 4) Insert one end of the fiber grating I101 on the transmission fiber I103 into one hole of the double-hole support tube, and insert one end of the fiber grating II102 on the transmission fiber II104 into the other hole of the double-hole support tube.

[0095] 5) Curing the high-temperature adhesive in a high-temperature oven to form a high-temperature adhesive bead 107 at one end of the double-hole support tube 105.

[0096] The method for using a high-speed dynamic total temperature measurement system based on fiber Bragg gratings includes the following steps:

[0097] 1) Insert the fiber grating high-frequency response total temperature probe 1 into the flow field to be measured, so that fiber grating I101 and fiber grating II102 are facing the direction of the high-speed airflow.

[0098] 2) The high-speed airflow stops at the end of the fiber grating high-frequency response total temperature probe 1, and the kinetic energy is converted into internal energy. Through heat transfer, the heat is transferred to fiber grating I101 and fiber grating II102, so that fiber grating I101 and fiber grating II102 generate fiber grating spectral signal I and fiber grating spectral signal II carrying temperature information, respectively. The fiber grating spectral signal I and fiber grating spectral signal II carrying temperature information are transmitted to fiber grating high-speed demodulation system 2 through transmission fiber I103 and transmission fiber II104, respectively.

[0099] 3) The fiber Bragg grating high-speed demodulation system 2 converts the fiber Bragg grating spectral signal I and fiber Bragg grating spectral signal II carrying temperature information into electrical signal I and electrical signal II carrying temperature information, and transmits them to the host computer 3;

[0100] The fiber grating high-speed demodulation system 2 uses edge filtering to demodulate the fiber grating spectral signal I and fiber grating spectral signal II carrying temperature information.

[0101] 4) The host computer 3 performs temperature calculations on electrical signals I and II carrying temperature information to obtain the total airflow temperature. The steps include:

[0102] 4.1) Establish the thermal conductivity differential equation for the fiber grating, namely:

[0103] (2)

[0104] In the formula, denoted as ρ, where c is the density of the fiber Bragg grating material; ρ is the specific heat of the fiber Bragg grating material; V is the volume of the section where the fiber Bragg grating exchanges heat with the airflow; F is the area of ​​the section where the fiber Bragg grating exchanges heat with the airflow; and h is the convective heat transfer coefficient between the fiber Bragg grating and the airflow. This refers to the internal temperature of the fiber grating. The airflow temperature;

[0105] 4.2) The host computer reconstructs the temperature information carried by electrical signals I and II at time τ, obtaining:

[0106] (3)

[0107] (4)

[0108] In the formula, for The actual temperature of the airflow at any given moment; for The temperature information carried by electrical signal I and electrical signal II at any given moment;

[0109] 4.3) Introducing aerodynamic parameters Substituting these values ​​into formulas (3)-(4), we obtain:

[0110] (5)

[0111] (6)

[0112] 4.4) Ratio formulas (5) and (6) and substitute them into the fiber grating temperature-wavelength formula to obtain the total airflow temperature. ,Right now:

[0113] (7)

[0114] In the formula, These represent the volumes of fiber grating I101 and the airflow convection heat transfer section, and the volumes of fiber grating II102 and the airflow convection heat transfer section, respectively.

[0115] Example 2:

[0116] A high-speed airflow total temperature measurement system based on a combined fiber Bragg grating includes a combined fiber Bragg grating high-frequency response total temperature probe, a transmission optical fiber, a fiber Bragg grating high-speed demodulation system, and a host computer.

[0117] The combined fiber Bragg grating high-frequency response total temperature probe mainly consists of a dual-hole support tube, transmission optical fibers, and fiber Bragg gratings. Each hole in the dual-hole support tube contains a transmission optical fiber, and the two transmission optical fibers are made of the same material but have different diameters. At the end of each transmission optical fiber is a fiber Bragg grating of about 2 mm in length, which is the temperature sensing element of the probe. Placing the fiber Bragg grating at the top of the fiber allows for the fastest temperature sensing. Using a short-pitch grating can reduce errors caused by uneven temperature distribution of the grating. High-temperature adhesive is filled between the dual-hole support tube and the transmission optical fibers. The high-temperature adhesive forms a high-temperature adhesive bead at one end of the dual-hole support tube. The dual-hole support tube can be a dual-hole ceramic tube.

[0118] The transmission fiber is a single-mode fiber multi-core armored optical cable.

[0119] The fiber Bragg grating high-speed demodulation system has multiple channels, enabling high-speed parallel processing of two fiber Bragg grating spectral signals.

[0120] The host computer is a computer with a demodulation system control program and a fiber Bragg grating fast and high-precision demodulation program.

[0121] The high-speed airflow total temperature measurement method based on combined fiber gratings involves measuring the center wavelength of the airflow at the same moment and the center wavelength offset rate at that moment using two fiber gratings with different diameters whose temperature-center wavelength curves are known. This allows the actual temperature of the airflow to be inferred by measuring the center wavelength of the airflow at the same moment and the center wavelength offset rate at that moment. This achieves the effect that the response time of the entire system is much smaller than that of a single fiber grating total temperature measurement system.

[0122] The high-speed dynamic total temperature measurement system and method based on fiber Bragg grating combinations includes, but is not limited to, the above-mentioned measurement system and method based on dual fiber Bragg gratings. Other dynamic total temperature measurement systems based on multiple fiber Bragg gratings are within the scope of this invention.

[0123] The function of each component in the system:

[0124] The combined fiber grating high-frequency response total temperature probe is the temperature sensing part of the entire system. It comes into direct contact with the airflow and converts temperature information into fiber grating reflection spectrum information.

[0125] In a combined fiber Bragg grating total temperature probe, the two fiber Bragg gratings are made of the same material but have different diameters, and therefore have different time constants. When measuring the temperature at the same location, the two fiber Bragg gratings indicate different temperatures at the same time. By measuring the temperature response curves of the two fiber Bragg gratings, the system can be compensated in real time.

[0126] The optical fiber is used to transmit fiber optic spectral signals that carry temperature information.

[0127] The fiber Bragg grating high-speed demodulation system is mainly responsible for acquiring the fiber Bragg grating spectrum, converting the optical signal into an electrical signal, and then transmitting it to the host computer for temperature calculation.

[0128] The host computer controls the demodulation system, performs fast and high-precision demodulation of spectral signals, and calculates, displays, and stores airflow temperature in real time.

[0129] Example 3:

[0130] Fabrication method of combined fiber optic grating total temperature probe

[0131] 1) Prepare materials (including two optical fibers of different diameters, a double-hole support tube, and high-temperature adhesive).

[0132] 2) Write a fiber optic grating about 2 mm long at the ends of each of the two transmission optical fibers.

[0133] 3) Determine and mark the relative positions of the double-hole support tube and the transmission optical fiber on the precision displacement stage.

[0134] 4) Apply high-temperature adhesive to the marked area of ​​the transmission fiber.

[0135] 5) Insert one end of the two transmission optical fibers with the fiber grating engraved on them into the two holes of the double-hole support tube respectively.

[0136] 6) Cur the high-temperature adhesive in a high-temperature oven.

[0137] 7) Apply high-temperature adhesive to the tail end of the double-hole support tube and cure it in a high-temperature oven to form high-temperature adhesive beads.

[0138] Example 4:

[0139] The principle of a high-speed airflow total temperature measurement method based on combined fiber Bragg gratings:

[0140] Fiber Bragg grating temperature measurement principle:

[0141] like Figure 3 A fiber grating is essentially a section of optical fiber with a periodically changing core refractive index. When a broadband beam of light (the incident spectrum in the figure) passes through a fiber grating, light that meets the phase-matching condition of the fiber grating is strongly reflected; light that does not meet the condition is reflected back only by a very weak portion due to phase mismatch. The monochromatic light reflected back by the grating (the reflected spectrum in the figure) acts like a narrow-band mirror.

[0142] The center wavelength of the reflected light With the period of refractive index change of the grating and the effective refractive index of the fiber core The following relationship exists:

[0143] (1)

[0144] In the formula, The wavelength reflected by the FBG. It is the grating period. It is the effective refractive index of the fiber Bragg grating.

[0145] When the temperature around a fiber Bragg grating changes, it causes variations in the grating period and the effective refractive index of the fiber core, thus altering the reflected wavelength. The change in the Bragg wavelength of the fiber Bragg grating is linearly related to the change in ambient temperature. By detecting the Bragg wavelength of the fiber Bragg grating, the corresponding temperature can be measured.

[0146] (2)

[0147] In the formula, This represents the temperature sensitivity coefficient of the fiber Bragg grating.

[0148] Principle of dynamic airflow temperature measurement using a dual fiber optic total temperature probe:

[0149] Dual fiber Bragg gratings measure the temperature at the same point in space using two fiber Bragg gratings made of the same material (i.e., with the same density, specific heat capacity, thermal conductivity, etc.) but with different diameters. By establishing a zero-dimensional heat transfer model and based on the lumped parameter method, dynamic temperature measurement can be achieved.

[0150] Based on the lumped parameter method, the thermal conductivity differential equation of the fiber grating is:

[0151] (3)

[0152] In the formula, —Density of fiber optic grating materials ;

[0153] c—Specific heat of fiber grating material ;

[0154] V—Volume of the fiber optic grating and the airflow convection heat transfer section. ;

[0155] F—The area of ​​the fiber optic grating and the airflow convection heat transfer section. ;

[0156] h—the convective heat transfer coefficient between the fiber grating and the airflow. ;

[0157] — Internal temperature of the fiber grating, K;

[0158] —Airflow temperature, K;

[0159] At time τ, the airflow temperature measured at the same point using a dual fiber grating is:

[0160] (4)

[0161] (5)

[0162] In the formula, — The actual temperature of the airflow at any given time, in K;

[0163] — The measured temperature, in K, of the two fiber Bragg gratings at any given time;

[0164] The two fiber gratings are close in position and have a small temperature gradient, so aerodynamic parameters are introduced. , Fiber gratings of the same material but different diameters are identical under the same conditions. Substituting into equations (4) and (5), we get...

[0165] (6)

[0166] (7)

[0167] Comparing equations (6) and (7) and substituting them into the fiber grating temperature-wavelength formula, we obtain:

[0168] (8)

[0169] In equation (8), All are known; For fiber optic gratings in The center wavelength of the reflection spectrum at time; , The rate of change of the center wavelength of the fiber grating at the measured moment with time can be obtained by the finite difference method. , The temperature sensitivity coefficient of the fiber Bragg grating. , The intercept of the fiber grating temperature-wavelength curve can be obtained through fiber grating calibration experiments; the corrected actual airflow temperature value can be obtained through equation (8).

[0170] The measurement results of airflow at 200℃ were simulated using two fiber gratings with a length of 2mm and diameters of 50um and 125um, respectively. The results were then substituted into equation (8) to obtain the corrected airflow temperature. The results are as follows: Figure 4 As can be seen, the time constant of the corrected curve is significantly smaller than the time constant of the fiber grating used.

[0171] Example 5:

[0172] A method for measuring the total temperature of high-speed airflow based on a combined fiber grating is described in Example 1. In order to achieve rapid acquisition of the center wavelength of the fiber grating, an intensity method can be used to demodulate it. A typical intensity demodulation method is the edge filtering method.

[0173] The demodulation principle of edge filtering is based on the functional relationship between the output light intensity and wavelength. See the basic structure below. Figure 8 For demodulation principles, please refer to [link / reference]. Figure 9 By utilizing the linear (or near-linear) filtering characteristics of filters within a certain wavelength range, the change in the center wavelength of the reflected signal from the fiber Bragg grating sensor is converted into a change in optical power, thereby achieving intensity demodulation of the fiber Bragg grating sensor.

[0174] The light emitted from the light source is reflected by the fiber Bragg grating sensor and then split into two paths by the coupler. One path is directly received by the photodetector D1 and used as a reference to compensate for intensity fluctuations. The other path passes through a volumetric optical linear filter, which filters the light according to the wavelength ratio. This filter has a wavelength-dependent transmittance, and the linearized model of the filtering function can be expressed as:

[0175] (9)

[0176] Where A is the filter slope. exist The value is equal to zero.

[0177] Assume the reflected light from the FBG has a spectral width Δλ and a center wavelength λ. B If the Gaussian function is used, then the output intensity of the filtered light and the reference beam can be expressed as:

[0178] (10)

[0179] (11)

[0180] The intensity of light incident on the Bragg grating. The reflectivity of the grating is given. The output of the reference arm remains constant as the input wavelength changes. The ratio of the two outputs is:

[0181] (12)

[0182] As can be seen from equation (12), the output will vary with the input wavelength. It changes linearly with the offset. That is... and direct measurement value I F / I R The relationship is linear, from which we can deduce value.

[0183] Example 6:

[0184] See Figure 6 The process of applying a high-frequency response total temperature probe based on a combined fiber grating to measure the high-speed dynamic temperature inside an aero-engine is as follows:

[0185] First, a high-frequency response total temperature probe based on a combined fiber Bragg grating is installed on a bracket. Then, the bracket is inserted into the internal cavity of the aero-engine, so that the fiber Bragg grating faces the direction of the high-speed airflow. The armored transmission fiber is connected to the high-speed demodulator, and the demodulator is connected to the computer via a network cable.

[0186] The high-speed airflow stagnates at the tip of the total temperature probe, converting kinetic energy into internal energy. Through heat transfer, the heat is transferred to the temperature-sensing fiber optic grating. The broadband light provided by the demodulator is transmitted to the fiber optic grating via the transmission fiber. The fiber optic grating senses the temperature change and reflects narrowband light containing temperature information. The demodulator reads the spectral information of the reflected light and transmits it to the computer via a network cable.

[0187] The computer reads a certain number of measurements from two fiber Bragg gratings and fits these measurements. The fitted curve, obtained after smoothing the measurements from the two fiber Bragg gratings, is then input into the dual fiber Bragg grating reverse calculation module for output.

[0188] Example 7:

[0189] The high-speed dynamic total temperature measurement system based on fiber Bragg gratings includes a fiber Bragg grating high-frequency response total temperature probe 1, a fiber Bragg grating high-speed demodulation system 2, and a host computer 3.

[0190] The fiber grating high-frequency response total temperature probe 1 includes fiber grating I101, fiber grating II102, transmission fiber I103, and transmission fiber II104;

[0191] The fiber gratings I101 and II102 monitor airflow temperature information and transmit the fiber grating spectral signal I and fiber grating spectral signal II carrying temperature information to the fiber grating high-speed demodulation system 2 through transmission fiber I103 and transmission fiber II104, respectively.

[0192] The fiber Bragg grating high-speed demodulation system 2 converts the fiber Bragg grating spectral signal I and fiber Bragg grating spectral signal II carrying temperature information into electrical signal I and electrical signal II carrying temperature information, and transmits them to the host computer 3.

[0193] The host computer 3 performs temperature calculations on electrical signals I and II carrying temperature information to obtain the total airflow temperature.

[0194] Example 8:

[0195] The high-speed dynamic total temperature measurement system based on fiber Bragg grating combination is described in Example 7. The fiber Bragg grating high-frequency response total temperature probe 1 also includes a double-hole support tube 105.

[0196] The end of the transmission optical fiber I103 is engraved with a fiber grating I101;

[0197] One end of the transmission optical fiber I103, on which the fiber grating I101 is engraved, is inserted into one hole of the double-hole support tube 105.

[0198] The transmission optical fiber I103 and the transmission optical fiber II104 are made of the same material but have different diameters;

[0199] The end of the transmission optical fiber II104 is engraved with a fiber grating II102;

[0200] One end of the transmission optical fiber II104, on which the fiber grating II102 is inscribed, is inserted into the other hole of the double-hole support tube 105.

[0201] The dual-hole support tube 105 has a transmission optical fiber I103 placed in one hole and a transmission optical fiber II104 placed in the other hole.

[0202] Example 9:

[0203] The high-speed dynamic total temperature measurement system based on fiber Bragg grating combination is described in Example 7. The fiber Bragg grating high-frequency response total temperature probe 1 also includes high-temperature adhesive 106.

[0204] The high-temperature adhesive 106 is filled between the double-hole support tube 105 and the transmission optical fiber I103 and transmission optical fiber II104.

[0205] The high-temperature adhesive forms a high-temperature adhesive bead 107 at one end of the double-hole support tube 105.

[0206] Example 10:

[0207] The high-speed dynamic total temperature measurement system based on fiber Bragg grating combination is described in Example 7. The transmission fiber I103 and transmission fiber II104 include, but are not limited to, single-mode fiber.

[0208] Example 11:

[0209] The high-speed dynamic total temperature measurement system based on fiber Bragg gratings is described in Example 7. The high-speed demodulation system of the fiber Bragg gratings has multiple signal channels, thereby realizing high-speed parallel processing of several fiber Bragg grating spectral signals.

[0210] Example 12:

[0211] The high-speed dynamic total temperature measurement system based on fiber Bragg grating combination is described in Example 7. The host computer 3 is used to control the operation of the fiber Bragg grating high-speed demodulation system 2.

[0212] Example 13:

[0213] The high-speed dynamic total temperature measurement system based on fiber Bragg gratings is described in Example 7. The fabrication steps of the fiber Bragg grating high-frequency response total temperature probe 1 are as follows:

[0214] 1. Write fiber Bragg grating I101 at the end of transmission fiber I103; write fiber Bragg grating II102 at the end of transmission fiber II104;

[0215] 2. Determine and mark the relative positions of the double-hole support tube 105, transmission optical fiber I103 and transmission optical fiber II104 on the precision displacement stage.

[0216] 3. Apply high-temperature adhesive to the marked areas on transmission optical fibers I103 and II104;

[0217] 4. Insert one end of the fiber grating I101 on the transmission fiber I103 into one hole of the double-hole support tube, and insert one end of the fiber grating II102 on the transmission fiber II104 into the other hole of the double-hole support tube.

[0218] 5. Cure the high-temperature adhesive in a high-temperature oven to form a high-temperature adhesive bead 107 at one end of the double-hole support tube 105.

[0219] Example 14:

[0220] The high-speed dynamic total temperature measurement system based on fiber Bragg grating combination is described in Example 7, where the total temperature of the airflow is... Satisfy the following formula:

[0221] (1)

[0222] In the formula, These represent the volumes of fiber grating I101 and the airflow convection heat transfer section, and the volumes of fiber grating II102 and the airflow convection heat transfer section, respectively. These represent the areas of fiber grating I101 and the airflow convection heat transfer section, and the areas of fiber grating II102 and the airflow convection heat transfer section, respectively. For fiber optic gratings in The center wavelength of the reflection spectrum at time; , These represent the rates of change of the center wavelengths of fiber gratings I101 and II102 over time at the measured moments, respectively. , These represent the temperature sensitivity coefficients of fiber grating I101 and fiber grating II102, respectively. , These represent the intercepts of the temperature-wavelength curves for fiber gratings I101 and II102, respectively. The diameters of fiber grating I101 and fiber grating II102 are given.

[0223] Example 15:

[0224] The method for using a high-speed dynamic total temperature measurement system based on fiber Bragg gratings includes the following steps:

[0225] 1. Insert the fiber grating high-frequency response total temperature probe 1 into the flow field to be measured, so that fiber grating I101 and fiber grating II102 are facing the direction of the high-speed airflow.

[0226] 2. The high-speed airflow stops at the end of the fiber grating high-frequency response total temperature probe 1, and the kinetic energy is converted into internal energy. Through heat transfer, the heat is transferred to fiber grating I101 and fiber grating II102, so that fiber grating I101 and fiber grating II102 generate fiber grating spectral signal I and fiber grating spectral signal II carrying temperature information, respectively. The fiber grating spectral signal I and fiber grating spectral signal II carrying temperature information are then transmitted to the fiber grating high-speed demodulation system 2 through transmission fiber I103 and transmission fiber II104, respectively.

[0227] The fiber Bragg grating high-speed demodulation system 2 described above converts the fiber Bragg grating spectral signal I and fiber Bragg grating spectral signal II carrying temperature information into electrical signal I and electrical signal II carrying temperature information, and transmits them to the host computer 3.

[0228] 4. The host computer 3 performs temperature calculation on electrical signals I and II carrying temperature information to obtain the total airflow temperature. The steps include:

[0229] 4.1) Establish the thermal conductivity differential equation for the fiber grating, namely:

[0230] (2)

[0231] In the formula, denoted as ρ, where c is the density of the fiber Bragg grating material; ρ is the specific heat of the fiber Bragg grating material; V is the volume of the section where the fiber Bragg grating exchanges heat with the airflow; F is the area of ​​the section where the fiber Bragg grating exchanges heat with the airflow; and h is the convective heat transfer coefficient between the fiber Bragg grating and the airflow. This refers to the internal temperature of the fiber grating. The airflow temperature;

[0232] 4.2) The host computer reconstructs the temperature information carried by electrical signals I and II at time τ, obtaining:

[0233] (3)

[0234] (4)

[0235] In the formula, for The actual temperature of the airflow at any given moment; for The temperature information carried by electrical signal I and electrical signal II at any given moment; denoted as c1 and c2, respectively; denoted as c1 and c2, respectively; denoted as h1 and h2, respectively; denoted as h1 and h2, respectively; denoted as F1 and F2, respectively; denoted as F1 and F2, respectively; denoted as V1 and V2, respectively; denoted as V1 and V2, respectively; denoted as V1 and V2, respectively; denoted as V1 and V2, respectively; denoted as c1 and c2, respectively; denoted as c1 and c2, respectively; denoted as c1 and c2, respectively; denoted as c1 and c2, respectively; denoted as c1 and c2, respectively; denoted as c1 and c2, respectively; denoted as h1 and h ...

[0236] 4.3) Introducing aerodynamic parameters Substituting these values ​​into formulas (3)-(4), we obtain:

[0237] (5)

[0238] (6)

[0239] In the formula, D is the diameter of the fiber grating;

[0240] 4.4) Ratio formulas (5) and (6) and substitute them into the fiber grating temperature-wavelength formula to obtain the total airflow temperature. ,Right now:

[0241] (7)

[0242] In the formula, These represent the volumes of fiber grating I101 and the airflow convection heat transfer section, and the volumes of fiber grating II102 and the airflow convection heat transfer section, respectively.

[0243] Example 16:

[0244] The main contents of the high-speed dynamic total temperature measurement system based on fiber Bragg grating combination are described in Example 15. In this example, the high-speed demodulation system 2 of fiber Bragg grating uses the edge filtering method to demodulate the fiber Bragg grating spectral signal I and the fiber Bragg grating spectral signal II carrying temperature information.

Claims

1. A high-speed dynamic total temperature measurement system based on fiber grating combination, characterized in that: It comprises a fiber grating high-frequency response total temperature probe (1), a fiber grating high-speed demodulation system (2) and a host computer (3). The fiber grating high-frequency response total temperature probe (1) comprises a fiber grating I (101), a fiber grating II (102), a transmission fiber I (103) and a transmission fiber II (104). The fiber grating I (101) and the fiber grating II (102) monitor airflow temperature information and transmit fiber grating spectrum signals I and II carrying temperature information to the fiber grating high-speed demodulation system (2) through the transmission fiber I (103) and the transmission fiber II (104) respectively. The fiber grating high-speed demodulation system (2) converts the fiber grating spectrum signals I and II carrying temperature information into electrical signals I and II carrying temperature information and transmits them to the host computer (3). The host computer (3) calculates the temperature of the electrical signals I and II carrying temperature information to obtain the total temperature of the airflow. The fiber grating high-frequency response total temperature probe (1) further comprises a double-hole support tube (105). The end of the transmission fiber I (103) is inscribed with the fiber grating I (101). The end of the transmission fiber I (103) inscribed with the fiber grating I (101) is inserted into one hole of the double-hole support tube (105). The transmission fiber I (103) and the transmission fiber II (104) are made of the same material but have different diameters. The end of the transmission fiber II (104) is inscribed with the fiber grating II (102). The end of the transmission fiber II (104) inscribed with the fiber grating II (102) is inserted into the other hole of the double-hole support tube (105). The double-hole support tube (105) has the transmission fiber I (103) placed in one hole and the transmission fiber II (104) placed in the other hole.

2. The high-speed dynamic total temperature measurement system based on fiber grating combination according to claim 1, characterized in that, The fiber grating high-frequency response total temperature probe (1) further comprises high-temperature glue (106). The high-temperature glue (106) is filled between the double-hole support tube (105) and the transmission fiber I (103) and the transmission fiber II (104). The high-temperature glue forms a high-temperature glue bead (107) at one end of the double-hole support tube (105).

3. The high-speed dynamic total temperature measurement system based on fiber grating combination according to claim 1, characterized in that, The transmission fiber I (103) and the transmission fiber II (104) include but are not limited to single-mode optical fibers.

4. The high-speed dynamic total temperature measurement system based on fiber grating combination according to claim 1, characterized in that, The fiber grating high-speed demodulation system has multiple signal channels, thereby realizing high-speed parallel processing of several fiber grating spectrum signals.

5. The high-speed dynamic total temperature measurement system based on fiber grating combination according to claim 1, characterized in that, The host computer (3) is used to control the operation of the fiber grating high-speed demodulation system (2).

6. The high speed dynamic total temperature measurement system based on fiber grating combination according to claim 1, characterized in that, The manufacturing steps of the fiber grating high-frequency response total temperature probe (1) are as follows: Step 1) inscribe the fiber grating I (101) at the end of the transmission fiber I (103) and inscribe the fiber grating II (102) at the end of the transmission fiber II (104); Step 2) determine the relative positions of the double-hole support tube (105), the transmission fiber I (103) and the transmission fiber II (104) on a precision displacement table and mark them; Step 3) apply high-temperature glue at the marked positions of the transmission fiber I (103) and the transmission fiber II (104). Step 4) one end of the transmission fiber I (103) on which the fiber grating I (101) is inscribed is inserted into one hole of the double-hole support tube, and one end of the transmission fiber II (104) on which the fiber grating II (102) is inscribed is inserted into the other hole of the double-hole support tube; Step 5) a high-temperature furnace is used to cure the high-temperature glue, so as to form a high-temperature glue bead (107) at one end of the double-hole support tube (105).

7. The high-speed dynamic total temperature measurement system based on fiber grating combination according to claim 1, characterized in that, Total air temperature satisfies the following equation: （1） In the formula, respectively represent the volume of the fiber grating I (101) and the air flow convection heat exchange part, the volume of the fiber grating II (102) and the air flow convection heat exchange part; respectively represent the area of the fiber grating I (101) and the air flow convection heat exchange part, the area of the fiber grating II (102) and the air flow convection heat exchange part; is the reflection spectrum center wavelength of the fiber grating at the moment t; is the reflection spectrum center wavelength of the fiber grating at the moment t; , respectively represent the rate of change of the center wavelength of the fiber grating I (101) and the fiber grating II (102) with time at the measured moment t; , respectively represent the temperature sensitivity coefficient of the fiber grating I (101) and the fiber grating II (102); , respectively represent the temperature-wavelength curve intercept of the fiber grating I (101) and the fiber grating II (102); is the diameter of the fiber grating I (101) and the fiber grating II (102).

8. The method of using a high speed dynamic total temperature measurement system based on fiber grating combination according to any one of claims 1 to 7, characterized in that, The method comprises the following steps: Step 1) the fiber grating high-frequency response total temperature probe (1) is inserted into a flow field to be measured, so that the fiber grating I (101) and the fiber grating II (102) face the direction of the incoming high-speed airflow; Step 2) the high-speed airflow stagnates at the end of the fiber grating high-frequency response total temperature probe (1), and the kinetic energy is converted into internal energy, and the heat is transferred to the fiber grating I (101) and the fiber grating II (102) through heat transfer, so that the fiber grating I (101) and the fiber grating II (102) generate fiber grating spectrum signals I and II carrying temperature information, respectively, and the fiber grating spectrum signals I and II carrying temperature information are transmitted to the fiber grating high-speed demodulation system (2) through the transmission fiber I (103) and the transmission fiber II (104), respectively; Step 3) the fiber grating high-speed demodulation system (2) converts the fiber grating spectrum signals I and II carrying temperature information into electrical signals I and II carrying temperature information, and transmits them to the host computer (3); Step 4) the host computer (3) calculates the temperature of the electrical signals I and II carrying temperature information to obtain the total temperature of the airflow, and the step comprises: Step 4.1) a heat conduction differential equation of the fiber grating is established, that is: （2） In the formula, is the density of the fiber grating material; c is the specific heat of the fiber grating material; V is the volume of the part of the fiber grating that exchanges heat with the airflow by convection; F is the area of the part of the fiber grating that exchanges heat with the airflow by convection; h is the convection heat exchange coefficient of the fiber grating and the airflow; is the temperature inside the fiber grating; is the temperature of the airflow; Step 4.2) the host computer (3) restores the temperature information carried by the electrical signals I and II at time τ to obtain: （3） （4） wherein is the actual temperature of the air flow at the moment; is the temperature information carried by the electrical signal I, electrical signal II at the moment; is the density of the fiber grating I (101), fiber grating II (102); c1, c2 are the specific heat of the fiber grating I (101), fiber grating II (102); h1, h2 are the convective heat transfer coefficients of the fiber grating I (101), fiber grating II (102) and the air flow; F1, F2 are the areas of the convective heat transfer parts of the fiber grating I (101), fiber grating II (102) and the air flow; V1, V2 are the volumes of the convective heat transfer parts of the fiber grating I (101), fiber grating II (102) and the air flow; Step 4.3) Introducing aerodynamic parameters and substituting into equations (3) - (4) gives: （5） （6） In the formula, D is the diameter of the fiber grating; Step 4.4) The formula (5) and formula (6) are compared, and the total temperature of the airflow is obtained by substituting the fiber grating temperature-wavelength formula That is: （7） In the formula, respectively represent the volume of the fiber grating I (101) and the volume of the air flow convection heat exchange part of the fiber grating II (102).

9. The method of using a high speed dynamic total temperature measurement system based on fiber grating combination according to claim 8, characterized in that, The fiber grating high-speed demodulation system (2) demodulates the fiber grating spectrum signals I and II carrying temperature information by using an edge filtering method.

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