Method for evaluating uncertainty of air inlet flow measurement of high-altitude test bed

Abstract

The invention discloses a high-altitude test bed air inlet flow measurement uncertainty evaluation method, which comprises the following steps of: 1, measuring air inlet flow by an orifice plate flowmeter in an engine test process; 2, calculating bypass flow QQ2 according to the test data of the existing bypass sensor measurement unit; 3, MATLBA software is used for solving a verification equation, calibration is carried out according to the air inlet flow measured in the step 1 and the bypass flow QQ2 at the corresponding moment calculated in the step 1, and a calibration model is obtained; step 4, adding uncertainty introduced by the calibration model on the basis of original measurement to obtain an uncertainty evaluation expression; the uncertainty comprises uncertainty introduced by orifice plate flowmeter measurement and uncertainty introduced by a calibration model. The technical problem that the uncertainty of air flow measurement of the air inlet system of the high-altitude test bed cannot be accurately evaluated in the prior art is solved.

Description

Technical Field

[0001] This invention belongs to the technical field of uncertainty assessment of air intake flow measurement on high-altitude test benches, and specifically relates to a method for assessing the uncertainty of air intake flow measurement on high-altitude test benches. Background Technology

[0002] High-altitude simulation test benches, as large-scale aero-engine testing facilities, can reproduce in-flight flight conditions on the ground to conduct high-altitude characteristic tests on aero-engines. These benches are core testing equipment for aero-engine research and development and repair. Intake flow rate, as a core control parameter of the high-altitude test bench, directly affects the accuracy of experimental conditions and the reliability of engine test data. Therefore, the intake system, as a key subsystem of the high-altitude test bench, is responsible for simulating the intake conditions of aero-engines. Intake flow rate parameters are important parameters for verifying engine performance and are key parameters for calculating engine thrust, combustion chamber efficiency, and emissions. Intake flow rate calibration ensures the accuracy of measurement data, thus providing a reliable basis for engine research and development and improvement.

[0003] For the calibration of airflow in intake systems, most current methods involve setting up calibration devices using flow meters and other equipment. There is still a lack of methods for calibration by calculating bypass flow rates, and existing technologies cannot accurately assess the uncertainty of airflow measurement after obtaining the calibration coefficient of the orifice plate flow meter. Airflow measurement uncertainty is a crucial indicator of its reliability and accuracy; excessively high uncertainty can lead to performance evaluation biases. Summary of the Invention

[0004] To overcome the aforementioned shortcomings of existing technologies and to meet the needs of high-altitude test runs of different types of engines, this invention proposes a method for evaluating the uncertainty of airflow measurement on a high-altitude test stand. Addressing the technical problem that existing technologies cannot accurately evaluate the uncertainty of airflow measurement in the airflow system of a high-altitude test stand, this invention provides a method for calibrating the airflow of the airflow system on a high-altitude test stand and evaluating the uncertainty after calibration.

[0005] This invention provides a method for evaluating the uncertainty of intake flow measurement on a high-altitude test bench. The measured flow rate is the main flow rate QQ1, which has two branches: branch one and branch two. Branch one leads to the high-altitude chamber and is controlled by valve QF7. Branch two is an exhaust pipe leading to external air and is controlled by valve QF8. The flow rate of branch two is the bypass flow rate QQ2. The sum of the opening degrees of QF7 and QF8 is 100%. When QF7 is fully closed, the steady-state main flow rate QQ1 is theoretically equal to the bypass flow rate QQ2. The method includes the following steps: Step 1: During engine testing, the intake air flow rate is measured by an orifice plate flow meter; Step 2: Calculate the bypass flow rate QQ2 based on the test data from the existing bypass sensor measurement unit; Step 3: Solve the verification equation using MATLBA software: Perform calibration based on the intake flow rate measured in Step 1 and the bypass flow rate QQ2 calculated in Step 1 at the corresponding time to obtain the calibration model; Step 4: Add the uncertainty introduced by the calibration model to the original measurement to obtain the uncertainty evaluation expression; the uncertainty includes the uncertainty introduced by the orifice plate flowmeter measurement and the uncertainty introduced by the calibration model.

[0006] Furthermore, the sensor measurement unit includes a temperature sensor, a static pressure sensor, and a total pressure sensor.

[0007] Furthermore, in step two, the specific method for calculating the bypass flow QQ2 is as follows: The measured data is the total temperature. static pressure Total pressure Then the static temperature can be calculated. : In formula (1) k For specific heat ratio, k =1.4 based on static temperature Find the Mach number : According to the definition of Mach number... Formula for calculating the speed of sound The flow rate of the bypass gas was calculated. : in The gas constant is... ; According to static pressure Calculate the density of the gas: Calculate the cross-sectional area of ​​the bypass pipe Thus, the bypass flow QQ2 can be calculated: Further, calculate the cross-sectional area of ​​the bypass pipe. The specific method is as follows: Use a micrometer to measure the inner diameter of the pipe, and calculate the cross-sectional area of ​​the bypass pipe according to the area formula. .

[0008] Furthermore, the specific method for obtaining the calibration model in step three is as follows: With regulating valve QF7 closed, under steady-state conditions, the bypass flow rate QQ2 and the main flow rate QQ1 are theoretically equal. Record the inlet flow rate QQ1 measured by the orifice plate flowmeter as data sample A. Calculate the bypass flow rate QQ2 at the corresponding time point according to step two, and use this as data sample B. Import the two data samples into MATLAB software. After aligning the time series of QQ1 and QQ2, construct a linear regression model using the least squares method and solve for the verification slope. Sum of check intercepts : Furthermore, the specific method for obtaining the uncertainty evaluation expression in step four is as follows: The formula for calculating measurement uncertainty is as follows: The inclusion factor k=2 covers approximately 95% of the confidence interval, and the combined standard uncertainty is... The calculation formula is as follows: In equation (8), To calibrate the standard uncertainty for intake flow measurement, This introduces the standard uncertainty when using bypass flow calibration tests.

[0009] Furthermore, the uncertainty of the intake flow rate measurement calibration standard. The following formula is used to calculate: In equation (9), The standard uncertainty introduced when measuring total temperature for bypass flow; according to the calibration certificate of the total temperature sensor, the resulting measurement error is... =±0.3%, following a uniform distribution, and assessed according to Category B, calculated using the following formula: The standard uncertainty introduced when measuring static pressure in the bypass pipeline; according to the calibration certificate of the pressure sensor, the measurement error is... =±0.3%, following a uniform distribution, and assessed according to Category B, calculated using the following formula: The standard uncertainty introduced when measuring the total pressure of the bypass pipeline; according to the calibration certificate of the pressure sensor, the measurement error is... =±0.3%, following a uniform distribution, and assessed according to Category B, calculated using the following formula: The standard uncertainty introduced when measuring the diameter of the bypass pipeline; according to the micrometer calibration certificate, the measurement error is... =±0.01mm, according to Class B assessment, calculated using the following formula: The combined uncertainty introduced when measuring the inlet air flow rate QQ1 using an orifice plate flow meter is calculated using the following formula: According to the Class A assessment, the deviation is calculated using the Bessel formula, and the average measurement value is taken as the measurement result. The following formula is used for calculation: Where: n represents the number of independent repeated measurements. This is the arithmetic mean of the measurement results.

[0010] According to the calibration certificate of the orifice plate flowmeter, the systematic error is... =±1.5%, according to Category B assessment, calculated using the following formula: Furthermore, the standard uncertainty introduced when using bypass flow calibration tests Based on the calibration data measured in n independent field tests, and categorized as Class A, the calculation formula is as follows: The working principle of this invention is: This invention is a bypass flow compensation calibration method for airflow calibration of the intake system of an upper-altitude test station. The method does not require the addition of any calibration equipment such as mass flow meters to the existing architecture of the upper-altitude test station. The bypass flow is calculated by real-time acquisition of monitoring data from the bypass sensor, and dynamic calibration is achieved by constructing a linear regression model between the bypass flow and the main flow using MATLAB. It also has the advantages of simple structure, low implementation cost and high measurement accuracy.

[0011] This invention also addresses the uncertainty assessment method for airflow in the intake system of an aerial test station. This method analyzes the physical architecture and measurement principle of the bypass flow calibration unit and the main flow measurement unit, quantitatively analyzes and models the sources of uncertainty in each key link, and constructs an airflow uncertainty model covering multiple dimensions such as sensor nonlinearity and environmental parameter interference, thereby achieving accurate assessment of airflow measurement uncertainty.

[0012] Compared with the prior art, the beneficial effects of the present invention are: This invention proposes a calibration method based on bypass flow compensation for situations where it is impossible to add a mass flow meter. This method achieves dynamic calibration of the main flow by calculating the bypass flow in real time and obtaining the calibration equation using MATLAB. It obtains the calibration coefficient of the orifice plate flow meter used for measuring the main flow, thus achieving calibration of the main flow. This method differs from conventional calibration methods that add calibration devices such as mass flow meters to the main flow. By fitting the bypass flow to calibrate the main flow, it effectively reduces the calibration cost of the main flow while ensuring accuracy.

[0013] This invention proposes a method for evaluating the measurement uncertainty of the main flow rate after obtaining the calibration coefficient of the main flow rate measured by the orifice plate flowmeter. This method comprehensively quantifies various error sources in air flow measurement and forms a systematic evaluation framework. The method mainly considers the random errors introduced by the calibration device and the calibration test process, analyzes and evaluates the error sources, and integrates them into quantifiable uncertainty evaluation indicators, providing a scientific basis for the reliability of experimental data. Attached Figure Description

[0014] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below.

[0015] Figure 1 This is a schematic diagram of the basic structure of the air intake system of a high-altitude test stand, illustrating the application of an uncertainty assessment method for air intake flow measurement on a high-altitude test stand according to an embodiment of the present invention.

[0016] Figure 2 This is a schematic diagram of a two-dimensional simulation model in a method for evaluating the uncertainty of airflow measurement on a high-altitude test bench according to an embodiment of the present invention. Detailed Implementation

[0017] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0018] like Figure 1 , Figure 2 As shown in the figure, an embodiment of the present invention provides a method for evaluating the uncertainty of airflow measurement on a high-altitude test bench, which applies the following methods: Figure 1The high-altitude test bench's air intake system measures the main flow rate QQ1. The main flow rate has two branches: Branch 1 and Branch 2. Branch 1 leads to the high-altitude chamber, controlled by valve QF7. Branch 2 is the exhaust pipe leading to external air, controlled by valve QF8. The flow rate of Branch 2 is the bypass flow rate QQ2. The sum of the opening degrees of QF7 and QF8 is 100%. Theoretically, with QF7 fully closed, the steady-state main flow rate QQ1 is equal to the bypass flow rate QQ2. The system includes the following steps: Step 1: During engine testing, the intake air flow rate is measured by an orifice plate flow meter; Step 2: Calculate the bypass flow rate QQ2 based on the test data from the existing bypass sensor measurement units; the sensor measurement units include a temperature sensor, a static pressure sensor, and a total pressure sensor. The specific method for calculating the bypass flow rate QQ2 is as follows: The measured data is the total temperature. static pressure Total pressure Then the static temperature can be calculated. : In formula (1) k For specific heat ratio, k =1.4 based on static temperature Find the Mach number : According to the definition of Mach number... Formula for calculating the speed of sound The flow rate of the bypass gas was calculated. : in The gas constant is... ; According to static pressure Calculate the density of the gas: Calculate the cross-sectional area of ​​the bypass pipe Thus, the bypass flow QQ2 can be calculated: Calculate the cross-sectional area of ​​the bypass pipe The specific method is as follows: Use a micrometer to measure the inner diameter of the pipe, and calculate the cross-sectional area of ​​the bypass pipe according to the area formula. .

[0019] Step 3: Solve the verification equation using MATLAB software: Based on the intake flow rate measured in Step 1 and the bypass flow rate QQ2 calculated at the corresponding time in Step 1, perform calibration to obtain the calibration model. Close the regulating valve QF7. Under steady-state conditions, the bypass flow rate QQ2 is theoretically equal to the main flow rate QQ1. Record the value of the intake flow rate QQ1 measured by the orifice plate flowmeter as data sample A. Calculate the bypass flow rate QQ2 at the corresponding time in Step 2 as data sample B. Import the two data samples into MATLAB software. After aligning the time series of QQ1 and QQ2, construct a linear regression model using the least squares method and solve for the verification slope. Sum of check intercepts : Step 4: Add the uncertainty introduced by the calibration model to the original measurement to obtain the uncertainty evaluation expression; the uncertainty includes the uncertainty introduced by the orifice plate flowmeter measurement and the uncertainty introduced by the calibration model.

[0020] The formula for calculating measurement uncertainty is as follows: The inclusion factor k=2 covers approximately 95% of the confidence interval, and the combined standard uncertainty is... The calculation formula is as follows: In equation (8), To calibrate the standard uncertainty for intake flow measurement, This introduces the standard uncertainty when using bypass flow calibration tests.

[0021] Inlet flow rate measurement calibration standard uncertainty The following formula is used to calculate: In equation (9), The standard uncertainty introduced when measuring total temperature for bypass flow; according to the calibration certificate of the total temperature sensor, the resulting measurement error is... =±0.3%, following a uniform distribution, and assessed according to Category B, calculated using the following formula: The standard uncertainty introduced when measuring static pressure in the bypass pipeline; according to the calibration certificate of the pressure sensor, the measurement error is... =±0.3%, following a uniform distribution, and assessed according to Category B, calculated using the following formula: The standard uncertainty introduced when measuring the total pressure of the bypass pipeline; according to the calibration certificate of the pressure sensor, the measurement error is... =±0.3%, following a uniform distribution, and assessed according to Category B, calculated using the following formula: The standard uncertainty introduced when measuring the diameter of the bypass pipeline; according to the micrometer calibration certificate, the measurement error is... =±0.01mm, according to Class B assessment, calculated using the following formula: The combined uncertainty introduced when measuring the inlet air flow rate QQ1 using an orifice plate flow meter is calculated using the following formula: According to the Class A assessment, the deviation is calculated using the Bessel formula, and the average measurement value is taken as the measurement result. The following formula is used for calculation: Where: n represents the number of independent repeated measurements. This is the arithmetic mean of the measurement results.

[0022] According to the calibration certificate of the orifice plate flowmeter, the systematic error is... =±1.5%, according to Category B assessment, calculated using the following formula: Standard uncertainty introduced when using bypass flow calibration test Based on the calibration data measured in n independent field tests, and categorized as Class A, the calculation formula is as follows: The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention 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 the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for evaluating the uncertainty of intake flow measurement on a high-altitude test bench, wherein the measured flow rate is the main flow rate QQ1, and the main flow rate has two branches, namely branch one and branch two. Branch one leads to the high-altitude chamber, and the regulating valve is QF7; branch two is an exhaust pipe leading to the outside air, and the regulating valve is QF8. The flow rate of branch two is the bypass flow rate QQ2, wherein... The sum of the opening degrees of QF7 and QF8 is 100%. When QF7 is fully closed, the steady-state main flow rate QQ1 is theoretically equal to the bypass flow rate QQ2. The system is characterized by the following steps: Step 1: During engine testing, the intake air flow rate is measured by an orifice plate flow meter; Step 2: Calculate the bypass flow rate QQ2 based on the test data from the existing bypass sensor measurement unit; Step 3: Solve the verification equation using MATLBA software: Perform calibration based on the intake flow rate measured in Step 1 and the bypass flow rate QQ2 calculated in Step 1 at the corresponding time to obtain the calibration model; Step 4: Add the uncertainty introduced by the calibration model to the original measurement to obtain the uncertainty evaluation expression; the uncertainty includes the uncertainty introduced by the orifice plate flowmeter measurement and the uncertainty introduced by the calibration model.

2. The method for evaluating the uncertainty of airflow measurement on a high-altitude test stand according to claim 1, characterized in that, The sensor measurement unit includes a temperature sensor, a static pressure sensor, and a total pressure sensor.

3. The method for evaluating the uncertainty of airflow measurement on a high-altitude test bench according to claim 1, characterized in that, In step two, the specific method for calculating the bypass flow QQ2 is as follows: The measured data is the total temperature. static pressure Total pressure Then the static temperature can be calculated. : (1)； In formula (1) k For specific heat ratio, k =1.4 based on static temperature Find the Mach number : (2)； According to the definition of Mach number... Formula for calculating the speed of sound The flow rate of the bypass gas was calculated. : (3)； in The gas constant is... ; According to static pressure Calculate the density of the gas: (4)； Calculate the cross-sectional area of ​​the bypass pipe Thus, the bypass flow QQ2 can be calculated: (5)。 4. The method for evaluating the uncertainty of airflow measurement on a high-altitude test stand according to claim 3, characterized in that, Calculate the cross-sectional area of ​​the bypass pipe The specific method is as follows: Use a micrometer to measure the inner diameter of the pipe, and calculate the cross-sectional area of ​​the bypass pipe according to the area formula. .

5. The method for evaluating the uncertainty of airflow measurement on a high-altitude test stand according to claim 1, characterized in that, The specific method for obtaining the calibration model in step three is as follows: With regulating valve QF7 closed, under steady-state conditions, the bypass flow rate QQ2 and the main flow rate QQ1 are theoretically equal. Record the inlet flow rate QQ1 measured by the orifice plate flowmeter as data sample A. Calculate the bypass flow rate QQ2 at the corresponding time point according to step two, and use this as data sample B. Import the two data samples into MATLAB software. After aligning the time series of QQ1 and QQ2, construct a linear regression model using the least squares method and solve for the verification slope. Sum of check intercepts : (6)。 6. The method for evaluating the uncertainty of airflow measurement on a high-altitude test stand according to claim 1, characterized in that, The specific method for obtaining the uncertainty evaluation expression in step four is as follows: The formula for calculating measurement uncertainty is as follows: (7)； The inclusion factor k=2 covers approximately 95% of the confidence interval, and the combined standard uncertainty is... The calculation formula is as follows: (8)； In equation (8), To calibrate the standard uncertainty for intake flow measurement, This introduces the standard uncertainty when using bypass flow calibration tests.

7. The method for evaluating the uncertainty of airflow measurement on a high-altitude test stand according to claim 6, characterized in that, Intake flow measurement calibration standard uncertainty The following formula is used to calculate: (9)； In equation (9), The standard uncertainty introduced when measuring total temperature for bypass flow; according to the calibration certificate of the total temperature sensor, the resulting measurement error is... =±0.3%, following a uniform distribution, and assessed according to Category B, calculated using the following formula: (10)； The standard uncertainty introduced when measuring static pressure in the bypass pipeline; according to the calibration certificate of the pressure sensor, the measurement error is... =±0.3%, following a uniform distribution, and assessed according to Category B, calculated using the following formula: (11)； The standard uncertainty introduced when measuring the total pressure of the bypass pipeline; according to the calibration certificate of the pressure sensor, the measurement error is... =±0.3%, following a uniform distribution, and assessed according to Category B, calculated using the following formula: (12) ； The standard uncertainty introduced when measuring the diameter of the bypass pipeline; according to the micrometer calibration certificate, the measurement error is... =±0.01mm, according to Class B assessment, calculated using the following formula: (13)； The combined uncertainty introduced when measuring the inlet air flow rate QQ1 using an orifice plate flow meter is calculated using the following formula: (14)； According to the Class A assessment, the deviation is calculated using the Bessel formula, and the average measurement value is taken as the measurement result. The following formula is used for calculation: (15)； Where: n represents the number of independent repeated measurements. This is the arithmetic mean of the measurement results. According to the calibration certificate of the orifice plate flowmeter, the systematic error is... =±1.5%, according to Category B assessment, calculated using the following formula: (16)。 8. The method for evaluating the uncertainty of airflow measurement on a high-altitude test bench according to claim 6, characterized in that, Standard uncertainty introduced when using bypass flow calibration test Based on the calibration data measured in n independent field tests, and categorized as Class A, the calculation formula is as follows: (17)。

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