Airflow total temperature sensing part measuring head and error decoupling analysis method

Abstract

The invention belongs to the technical field of metering, and particularly relates to an airflow total temperature sensing part measuring head and an error decoupling analysis method, the airflow total temperature sensing part measuring head comprises a stagnation chamber and a thermocouple arranged in the stagnation chamber, and the airflow total temperature sensing part measuring head further comprises a spiral shielding sheet fixedly installed in the stagnation chamber; a spiral airflow channel is formed between the spiral piece of the spiral shielding piece and the inner surface of the stagnation chamber, and the spiral shielding piece completely shields the visible range between the hot contact of the thermocouple and the external environment.

Description

Technical Field

[0001] This application belongs to the field of metrology technology, and specifically relates to a total airflow temperature sensing probe and an error decoupling analysis method. Background Technology

[0002] The development of aero-engines requires extensive testing of the entire engine and its components. Total airflow temperature is one of the key aerodynamic parameters that needs to be measured during these tests to determine the engine's operating state, evaluate its performance, and assess the compatibility between its components. With increasingly complex flow fields in engines, the requirements for the testing performance and accuracy of the sensing element are gradually increasing, highlighting the growing contradiction of inaccurate measurements and hindering the improvement of engine development capabilities. The main sources of error in the total airflow temperature sensing element include thermocouple static error, radiation error, thermal conduction error, and velocity error. Thermocouple static error is corrected through thermocouple static calibration. Radiation, thermal conduction, and velocity errors (hereinafter referred to as the three major errors) inevitably occur during the heat exchange process between the airflow and the measuring end, resulting from the combined effects of convective heat transfer, thermal radiation, and material thermal conduction. Therefore, to minimize these three major errors, the probe of the total airflow temperature testing sensing element has gradually developed into a ball-and-socket structure, a stagnation chamber structure, and a shielded structure (see...). Figures 7-10 The total error was determined by comparing the hot wind tunnel calibration test with the standard value.

[0003] The disadvantages of existing technologies include:

[0004] 1. Ball-and-socket structure: The thermocouple hot junction has a large visible range, poor shielding effect against the external environment, and the measurement results are easily affected by the radiation heat transfer of the external environment, resulting in large radiation errors. Therefore, this structure has low testing accuracy.

[0005] 2. Stagnation chamber structure: It cannot achieve complete shielding from the external environment. The visible range of the thermocouple hot junctions means that the measurement results are affected by the radiation heat transfer of the external environment, resulting in a large radiation error. Therefore, the test accuracy of this structure is low.

[0006] 3. Shielding structure: Because the air intake direction is perpendicular to the axis of the shielding, this shielding is not suitable for multi-point total temperature sensing parts and cannot realize flow field measurement;

[0007] 4. Since there is a coupling relationship between the three major errors, one approach is to use simulation to quantify the proportion of each error in the total error, but the accuracy of the simulation results lacks effective experimental verification; the other approach is to determine the total error by comparing the hot wind tunnel calibration test with the standard value, but it is impossible to separate the individual error components.

[0008] Note: The visible angle α of the thermocouple hot junction. The sector area covered by the visible angle α is the visible range. See Figure 10 . Summary of the Invention

[0009] To address the aforementioned problems, this application provides an airflow total temperature sensing probe, including a stagnation chamber and a thermocouple disposed therein, and further comprising:

[0010] A spiral shield is fixedly installed inside the stagnation chamber; a spiral airflow channel is formed between the spiral blades of the spiral shield and the inner surface of the stagnation chamber, and the spiral shield completely blocks the visible range between the thermal junction of the thermocouple and the external environment.

[0011] Preferably, the spiral shielding sheet includes a spiral sheet and upper and lower lugs located at its two ends respectively; the inner wall of the stagnation chamber is provided with a strip groove that mates with the upper and / or lower lugs for positioning and installing the spiral shielding sheet, and the upper lug is welded and fixed to the stagnation chamber.

[0012] Preferably, the inlet end of the stagnation chamber is provided with an inlet chamfer for rectifying the incoming airflow.

[0013] Preferably, the bottom of the stagnation chamber is provided with an exhaust port for discharging the airflow that has washed over the thermocouple hot contacts.

[0014] A method for decoupling and analyzing total temperature measurement errors, based on the aforementioned airflow total temperature sensing probe, achieves error decoupling by comparing a set of measuring points with different structural parameters, including the following steps:

[0015] Provide at least one benchmark measurement point and at least one comparison measurement point;

[0016] The total error of the benchmark and comparison measuring points was obtained simultaneously through the experiment.

[0017] Based on the structural differences between the benchmark measuring point and different comparison measuring points, a set of error component equations is established.

[0018] Solve the system of equations to decouple at least one independent error component of the reference measurement point.

[0019] Preferably, the comparison measurement points include:

[0020] The first comparison measuring point has the same structure as the benchmark measuring point, but the thermocouple filament immersed in the gas is longer, making its thermal conductivity error negligible.

[0021] By comparing the total error of the reference measuring point with that of the first comparison measuring point, and assuming that the radiation errors of the two are equal, the thermal conductivity error of the reference measuring point is decoupled.

[0022] Preferably, the comparison measurement points further include:

[0023] The second comparison measuring point has the same structure as the reference measuring point, but adds the spiral shielding sheet, making its radiation error negligible.

[0024] By comparing the total error of the reference measuring point with that of the second comparison measuring point, and assuming that the thermal conductivity errors of the two are equal, the radiation error of the reference measuring point is decoupled.

[0025] Preferably, the comparison measurement points further include:

[0026] The third comparative measuring point has a structure that combines a longer thermocouple wire and the spiral shielding sheet, making its thermal conductivity error and radiation error negligible.

[0027] The accuracy of the decoupling result is verified by comparing the total error between the benchmark measuring point and the third comparison measuring point, the sum of the decoupled thermal conduction error and radiation error, and the sum of the error components decoupled by claims 6 and 7.

[0028] Preferably, the method further includes the step of comparing the experimental results of the decoupled thermal conductivity error and radiation error with the calculation results of the corresponding theoretical calculation formula, so as to correct the coefficients or form of the theoretical calculation formula and improve the accuracy of the theoretical prediction.

[0029] A test system for implementing the total temperature measurement error decoupling analysis method, characterized in that the system comprises:

[0030] A set of total temperature sensing point measurement points includes at least one reference measurement point and multiple comparison measurement points with different structural parameters;

[0031] Multiple auxiliary temperature measuring points are arranged at key locations of the measuring points to monitor the heat sink temperature or cold end wall temperature;

[0032] The data acquisition and processing device is used to acquire temperature data at each measuring point and execute the calculation process of the error decoupling analysis.

[0033] This application addresses the issue that neither spherical socket structures nor stagnation chamber structures can completely shield against the external environment. A special spiral shielding plate is designed to both maintain airflow pathways and block the visible range of thermocouple hot contacts, achieving complete shielding of the hot contacts. In engineering terms, this can be approximated as eliminating radiation errors. Compared to shielded enclosure structures, this structure is suitable for both single-point and multi-point total temperature sensing units, enabling simultaneous measurement of multiple data points and flow field measurements. Based on the excellent radiation error elimination effect of the total temperature sensing unit probe structure with the spiral shielding plate, a decoupling test piece for the "three major errors" and an error decoupling analysis method are designed. Each error component is quantified through experimental means, which can be used to correct theoretical error calculation formulas. Furthermore, targeted designs can be implemented based on the proportion of each error component to reasonably avoid the most influential error components. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the sensor probe;

[0035] Figure 2 This is a schematic diagram of a spiral shielding sheet;

[0036] Figure 3 This is a schematic diagram of a stagnation chamber;

[0037] Figure 4 This is a diagram of the airflow path inside the probe structure;

[0038] Figure 5 This is the installation diagram of the error decoupling test piece for the total temperature sensing probe structure.

[0039] Figure 6 This is a flowchart of error decoupling analysis.

[0040] Figure 7 This is a schematic diagram of a ball-and-socket structure.

[0041] Figure 8 This is a schematic diagram of the stagnation chamber structure.

[0042] Figure 9 Schematic diagram of the shielding cover structure.

[0043] Figure 10 A schematic diagram of the visible angle α of the thermocouple hot junction. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application will be described in more detail below with reference to the accompanying drawings. In the drawings, the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The described embodiments are only some embodiments of this application, not all embodiments. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application. All other embodiments obtained by those skilled in the art based on the embodiments in this application without creative effort are within the scope of protection of this application. The embodiments of this application will be described in detail below with reference to the accompanying drawings. The complete technical solution of the total temperature sensing probe structure with a spiral shield and the error decoupling analysis method is as follows:

[0045] Structural Description

[0046] like Figure 1 As shown, the probe structure mainly consists of a spiral shield 1, a stagnation chamber 2, a thermocouple 3, and a ceramic tube 4.

[0047] like Figure 2The spiral shielding plate 1 features an upper lug 11, a lower lug 13, and a spiral plate 12. The upper lug 11 and lower lug 13 are used for positioning the spiral shielding plate 1 within the stagnation chamber 2. After installation, the upper lug 11 is welded to the stagnation chamber 2 for fixation. The spiral plate 12 forms a spiral airflow channel with the inner surface of the stagnation chamber 2, and can completely block the thermal junction of the thermocouple 3 from the visible range of the external environment. Figure 3 Top view.

[0048] like Figure 3 The stagnation chamber 2 has the features of an inlet chamfer 21, a strip groove 22, an exhaust port 23, and a stepped hole 24. The inlet chamfer 21 is used to rectify the incoming airflow and increase the insensitive angle; the strip groove 22 serves as the positioning structure of the spiral shield 1; the exhaust port 23 is the passage for the internal airflow to be discharged; and the stepped hole 24 is used to fix the ceramic tube 4.

[0049] The airflow path inside the probe structure is shown below. Figure 4 The airflow arrives at the inlet of stagnation chamber 2 from the far end, is rectified by the inlet chamfer 21, passes through the spiral channel formed by the spiral shield 1 and the inner surface of stagnation chamber 2, converges again and washes the hot junction of thermocouple 3, and finally exits through exhaust port 23. Explanation of the principle of error decoupling analysis method.

[0050] The formula for calculating the total temperature sensing element test error is:

[0051] (1)

[0052] In the formula, Total error Thermocouple static error Speed ​​error, Thermal conductivity error Radiation error

[0053] The purpose of error decoupling is to obtain The four error components, among which This can be obtained through static calibration of thermocouples; The total temperature recovery coefficient r can be obtained through wind tunnel calibration tests, and then calculated according to equation (2). Therefore, error decoupling can be simplified to... and Decoupling.

[0054] (2)

[0055] In the formula, r is the total temperature restitution coefficient; k is the adiabatic index; M is the Mach number of the airflow; T * Let K be the total temperature of the airflow.

[0056] The error decoupling test piece based on the total temperature sensing probe structure with a spiral shield is shown below. Figure 5 Among them, A1 to A4 are the main measuring points, and B1 to B4 are the auxiliary measuring points. To facilitate the arrangement of the auxiliary measuring points, the stagnation chambers of the main measuring points all adopt an "embedded" structure. Thermocouple static calibration and wind tunnel calibration tests were conducted on A1 to A4 respectively. and Then according to Figure 6 Error decoupling analysis process obtains respectively and This achieves error decoupling, and the specific principle is as follows.

[0057] Main measuring point setting instructions

[0058] Measurement point A1 serves as the reference measurement point, i.e., the object of test error decoupling;

[0059] Measuring point A2 has an increased length of the filament immersed in the gas compared to the reference measuring point, while other structures remain unchanged.

[0060] Measurement point A3 has an added shielding structure based on the reference measurement point, while other structures remain unchanged.

[0061] Measurement point A4, based on the benchmark measurement point, also features an added shielding structure and an extended length of the filament immersed in the gas.

[0062] Auxiliary measuring point setting instructions

[0063] In order to obtain the temperature of the key parts of the sensing part as the basis for error calculation, armored thermocouples were buried near the root of the measuring point (A1, A2, A4) at different depths to monitor the heat sink temperature of the measuring point (B1, B2, B4) as the basis for calculating the thermal conductivity error.

[0064] Armored thermocouples were buried near the measuring point with the shielded structure (between A3 and A4) to monitor the temperature of the shield (B3) as the basis for calculating the radiation error.

[0065] Principle Explanation

[0066] The total errors of A1 to A4 were obtained through hot air tunnel calibration tests. (n=1~4); Temperatures at auxiliary measuring points B1, B2 and B4 (n=1, 2, 4), i.e., the heat sink temperatures of A1, A2, and A4; the temperature of auxiliary measuring point B3. That is, the cold junction wall temperature of A3 and A4; the static error of A1 to A4 is obtained by static calibration of thermocouples respectively. (n=1~4); After obtaining the total temperature recovery coefficients of A1~A4 through the retemperature coefficient calibration test, the speed error is calculated according to formula (2). (n=1~4).

[0067] 1. Decoupling of thermal conductivity error

[0068] Compare the total error test results of A1 and A2.

[0069] (3)

[0070] (4)

[0071] A1 and A2 are identical in structure except for the length of the protruding filaments; therefore, their radiation deviations can be considered to be the same. The aspect ratio of the filament in A2 immersed in the gas is greater than 10. In engineering, the thermal conductivity error of A2 is considered negligible. Subtracting equations (3) and (4) will decouple the actual thermal conductivity deviation at measuring point A1, i.e.

[0072] (5)

[0073] 2. Radiation error decoupling

[0074] Compare the total error test results of A1 and A3:

[0075] (6)

[0076] Compared to A1, A3 has added shielding, but the rest of the structure is the same. Therefore, their thermal conductivity deviations can be considered to be the same. The A3 employs a total temperature sensing probe structure with a spiral shielding plate. In engineering practice, the radiation error of the A3 is considered negligible. Subtracting equations (3) and (6) will decouple the actual radiation error at measuring point A1, i.e.

[0077] (7)

[0078] Verify the accuracy of decoupling thermal conductivity error and radiation error.

[0079] Compare the total error test results of A1 and A4:

[0080] (8)

[0081] Compared to A1, A4 increases the length of the filament immersed in the gas and adds shielding. , Subtracting equations (3) and (8) yields the sum of the actual thermal conductivity error and radiation error at measuring point A1, i.e.:

[0082] (9)

[0083] By comparing equation (9) with the sum of equations (5) and (7), the accuracy of the thermal conductivity error and radiation error obtained from the decoupling in steps 3 and 4 can be verified.

[0084] Correction error theoretical calculation formula

[0085] The theoretical formula for calculating thermal conductivity error is:

[0086] (10)

[0087] The effective stagnation temperature of the airflow. Where is the heat sink temperature, L is the length of the thermocouple wire immersed in the gas, and α is the convective heat transfer coefficient between the gas and the thermocouple. U is the thermal conductivity of the thermocouple, U is the circumference of the thermocouple wire, and F is the cross-sectional area of ​​the thermocouple wire.

[0088] The theoretical formula for calculating radiation error is:

[0089] (11)

[0090] ε is the emissivity at the measurement end, and c0 is the absolute blackbody radiation coefficient. The temperature of the thermocouple junction. This refers to the cold end wall temperature.

[0091] The theoretical calculation results of equations (10) and (11) are compared with the experimental results of thermal conductivity error and radiation error to verify the accuracy of the theoretical calculation formula. The theoretical calculation formula can be corrected by iterating through multiple sets of experimental data.

[0092] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A total temperature sensing probe for a gas flow, comprising a stagnation chamber (2) and a thermocouple (3) arranged therein, characterized in that, Also comprising: A spiral shielding piece (1) is fixedly installed inside the stagnation chamber (2); the spiral piece (12) of the spiral shielding piece (1) and the inner surface of the stagnation chamber (2) form a spiral air flow channel, and the spiral shielding piece (1) completely shields the visible range between the hot junction of the thermocouple (3) and the external environment.

2. The total temperature sensing probe of claim 1, wherein The spiral shielding piece (1) comprises a spiral piece (12) and upper and lower lugs (11) and (13) at both ends thereof; the inner wall of the stagnation chamber (2) is provided with a strip-shaped groove (22) matched with the upper and / or lower lugs (11) and (13) for positioning and installing the spiral shielding piece (1), and the upper lug (11) is welded and fixed with the stagnation chamber (2).

3. The total temperature sensing probe of claim 1 or 2, wherein The inlet end of the stagnation chamber (2) is provided with an inlet chamfer (21) for flow regulation of the incoming airflow.

4. The total temperature sensing probe of claim 1 or 2, wherein The bottom of the stagnation chamber (2) is provided with an exhaust hole (23) for discharging the airflow washed over the hot junction of the thermocouple (3).

5. A total temperature measurement error decoupling analysis method, characterized in that, The method is based on the total temperature sensing probe of any one of claims 1-4, and error decoupling is achieved by comparing a group of measuring points with different structural parameters, comprising the following steps: providing at least one reference measuring point (A1) and at least one comparison measuring point; synchronously obtaining the total error (Qt) of the reference measuring point (A1) and the comparison measuring point through experiments; based on the structural difference between the reference measuring point (A1) and different comparison measuring points, establishing an error component equation group; solving the equation group to decouple at least one independent error component of the reference measuring point (A1).

6. The total temperature measurement error decoupling analysis method of claim 5, wherein, The comparison measuring point comprises: A first comparison measuring point (A2) has the same structure as the reference measuring point (A1), but the thermocouple is immersed in the gas with a longer wire length, so that the heat conduction error can be ignored; By comparing the total error of the reference measuring point (A1) and the first comparison measuring point (A2), and assuming that the radiation errors of the two are equal, the heat conduction error (Qc1) of the reference measuring point (A1) is decoupled.

7. The total temperature measurement error decoupling analysis method according to claim 5 or 6, characterized in that, The comparison measuring point further comprises: A second comparison measuring point (A3) has the same structure as the reference measuring point (A1), but is provided with the spiral shielding piece (1) of any one of claims 1-4, so that the radiation error can be ignored; By comparing the total error of the reference measuring point (A1) and the second comparison measuring point (A3), and assuming that the heat conduction errors of the two are equal, the radiation error (Qr1) of the reference measuring point (A1) is decoupled.

8. The total temperature measurement error decoupling analysis method of claim 7, wherein, The comparison measuring point further comprises: A third comparison measuring point (A4) has both a longer thermocouple wire and the spiral shielding piece (1), so that the heat conduction error and the radiation error can be ignored; By comparing the total error of the reference measuring point (A1) and the third comparison measuring point (A4), the sum of the heat conduction error and the radiation error is decoupled, and compared with the sum of the error components decoupled by claims 6 and 7 to verify the accuracy of the decoupling result.

9. The total temperature measurement error decoupling analysis method of claim 5, wherein, The method further comprises the steps of: comparing the test results of the decoupled heat conduction error and radiation error with the calculation results of the corresponding theoretical calculation formula, to correct the coefficients or forms of the theoretical calculation formula, and to improve the accuracy of the theoretical prediction.

10. A test system for implementing the total temperature measurement error decoupling analysis method according to any one of claims 5-9, characterized in that, The system comprises: a set of total temperature sensing points, including at least one reference point (A1) and a plurality of contrast points with different structural parameters; a plurality of auxiliary temperature sensing points (B1-B4) arranged at key positions of the sensing points, for monitoring the temperature of the heat sink or the cold end wall; a data acquisition and processing device for acquiring temperature data of each sensing point and executing the calculation process of the error decoupling analysis.

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