Equivalent nozzle detection method for precision detection of air flow measurement system

Abstract

The invention aims to provide an equivalent nozzle detection method for precision detection of an air flow measurement system, and belongs to the field of gas turbine detection. According to the method, a gas nozzle standard condition mass flow design value is taken as a reference, and in a high-precision mass flow test system, an air mass flow equivalent nozzle meeting the metering requirement is screened out through a mass flow conversion formula. And in the detected air mass flow testing system, the air at the inlet of the equivalent nozzle reaches the preset pressure, the steady-state air flow is kept, the real-time air mass flow is converted into the standard condition mass flow, the converted mass flow is compared with the standard flow value of the equivalent nozzle, and the relative error of the detected air mass flow testing system is analyzed. The method is good in standard flow repeatability, the precision reaches + / -0.5% or above, and the method is suitable for precision detection analysis of an air mass flow testing system.

Description

Technical Field

[0001] The present invention relates to a detection method, in particular to a gas turbine detection method. Background Art

[0002] During the development process or overhaul phase of the gas fuel gas turbine combustion chamber, it is necessary to test the performance of the gas nozzle through the gas nozzle flow test. Accurately testing the nozzle air flow data helps to better understand the nozzle flow characteristics and reduce the differences between the gas nozzles of the whole machine. The flow accuracy of the air flow test system has a great influence on the test results of the gas nozzle flow. Before the gas nozzle flow test, flow accuracy detection and analysis is required to understand the accuracy of the entire air flow test system.

[0003] There are three main measuring instruments in the gas nozzle air flow test system: temperature, pressure and flow meter. The range and accuracy have a greater impact on the accuracy of flow test. Temperature sensor parameters: including accuracy level, range and measurement point location; pressure sensor parameters: including accuracy level, range and measurement point location; flow meter parameters: flow accuracy level and range.

[0004] The air flowing through the flow meter is low-velocity air (Mach number is less than 0.2). Generally, a Coriolis mass flow meter that meets the accuracy requirements is selected based on the design flow of the gas nozzle.

[0005] The air flowing through the flow meter is high velocity air (Mach number is 1), and generally a critical Venturi nozzle flow meter that meets the accuracy requirements is selected based on the design flow of the gas nozzle.

[0006] It is understood that there is currently a Venturi nozzle flow calibrator for the purpose of flow calibration of the entire air flow test system. Patent document CN 109211372B (application number 201811340744.2) discloses a low-pressure critical flow Venturi nozzle calibration device, but the cost is high, the calibrator needs to be connected in series to the air pipeline, and the operation is complicated.

[0007] It is not convenient to use the gas nozzle to test the flow test system to analyze the flow accuracy status. Patent document CN109724789A (application number 201910060539.9) discloses an aero-derivative gas turbine fuel nozzle flow test system and method, which uses a new fuel nozzle as a benchmark to compare the fuel nozzle to be tested. Testing in this way is prone to cause fuel path blockage and can no longer be used as a standard flow part.

[0008] The state of the gas medium changes with the environmental conditions (atmospheric pressure, temperature and pressure). For the same gas nozzle in different seasons and different test locations, the test data often has a large relative deviation. Patent document CN113029547 B (application number 202110358682.3) discloses a portable gas fuel nozzle flow test device and a method of use. The conversion formula does not take into account the large difference in environmental conditions between standard conditions and low atmospheric pressure conditions, and there is a large conversion error. In fact, the influence of environmental factors on air flow testing has not been eliminated.

[0009] Currently, there is no universal and convenient high-precision flow standard, nor is there a universal method to analyze and detect the flow accuracy of air flow test benches. It is urgent to develop a technical solution that can quickly, accurately, and easily operate flow accuracy analysis and detection on existing air flow test benches without adding additional equipment. Summary of the invention

[0010] The purpose of the present invention is to provide an equivalent nozzle detection method for precision detection of an air flow measurement system which can solve the technical problems that the flow meter needs to be dismantled and is time-consuming in the past.

[0011] The object of the present invention is achieved in that:

[0012] The invention discloses an equivalent nozzle detection method for air flow measurement system accuracy detection, which is characterized by comprising the following steps:

[0013] (1) In a calibrated high-precision flow test system, screen equivalent nozzles that meet the accuracy and repeatability indicators;

[0014] (2) Select a reduced flow rate formula with a relatively small error to eliminate the influence of ambient atmospheric pressure and air flow temperature conditions on the reduced flow rate;

[0015] (3) Screen out equivalent nozzles whose converted standard flow rate is consistent with the designed flow rate of the gas nozzle and number them; record the test conditions, flow data and test time of the equivalent nozzles, thereby forming the standard flow data of the equivalent nozzles;

[0016] (4) Combine various typical environmental conditions, such as low pressure, low temperature, and air pressure close to standard conditions, to correct the standard flow data of the equivalent nozzle;

[0017] (5) Connect the equivalent nozzle to the air flow test system to be tested, adjust the test pressure condition to the design value, and perform the air flow test;

[0018] (6) The real-time air flow rate of the equivalent nozzle under the test condition is converted into the air flow rate under standard conditions, and compared with the standard flow data under standard conditions to analyze the flow accuracy of the air flow test system.

[0019] The present invention may also include:

[0020] 1. In step (1), the flow accuracy level of the high-precision flow test system is not less than 0.3, and the flow repeatability is ≤0.10%.

[0021] 2. The conversion flow rate formula in step (2) is determined based on the engineering fluid mechanics formula combined with test data, and the working fluid is dry air that does not require humidity correction;

[0022] The standard mass flow conversion formula is:

[0023] G s =G c α

[0024]

[0025] P1=△P+P0, P2=△P+101.325;

[0026] Where α is the mass flow conversion coefficient;

[0027] △P is the gauge pressure of the air inlet of the equivalent nozzle; P0 is the ambient atmospheric pressure; P1 is the absolute pressure of the inlet of the equivalent nozzle; P2 is the absolute pressure of the inlet of the equivalent nozzle under standard conditions; T1 is the temperature of the airflow flowing through the equivalent nozzle; T2 is the temperature of the airflow flowing through the equivalent nozzle under standard conditions; G c is the real-time mass flow rate of the equivalent nozzle; G S It is the standard mass flow rate after conversion of the equivalent nozzle.

[0028] The advantages of the present invention are: the present invention uses the value transfer principle of equivalent nozzle flow to quickly complete the air flow test bench accuracy (relative error) detection, which helps to grasp the accuracy of the air flow test bench. On this basis, the use of high-precision flow test equipment improves the air flow test accuracy of the gas nozzle and improves the interchangeability, which has high technical benefits. At the same time, it provides a basis for the accuracy status of the air flow test bench, provides powerful data for improving the air flow measurement accuracy, and reduces the dependence on imported flow meters and other test and measurement equipment. It has high economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is a flow chart of the present invention;

[0030] Figure 2a is a schematic diagram of an equivalent nozzle, Figure 2b It is the cross-sectional view of the equivalent nozzle of the example;

[0031] Figure 3 Schematic diagram of the test system;

[0032] Figure 4 Schematic diagram of air flow accuracy detection method. DETAILED DESCRIPTION

[0033] The present invention is described in more detail below with reference to the accompanying drawings:

[0034] Combination Figure 1-4 , design the equivalent nozzle structure according to the gas nozzle interface size and fuel channel size. Test in a calibrated higher precision flow test system to determine the basic size of the equivalent nozzle, and use materials with less deformation due to temperature changes to process the equivalent nozzle. After this high-precision air flow test, the accuracy and repeatability of the equivalent nozzle are assessed according to the requirements of the national metrology standard table (flow meter), and it is used as a flow standard to test the flow accuracy of the air flow test system that needs to be tested.

[0035] The present invention mainly comprises the following steps:

[0036] 1. In the calibrated higher precision flow test system, select equivalent nozzles that meet the accuracy and repeatability indicators according to the performance requirements specified in the national metrology technical specification "JJG 643-2024 Standard Table Method Flow Standard Device".

[0037] 2. Select a conversion flow formula with a small relative error to eliminate the influence of ambient atmospheric pressure and air flow temperature conditions on the conversion flow as much as possible.

[0038] 3. Select equivalent nozzles that meet the flow requirements (the converted standard flow is consistent with the designed flow of the gas nozzle) and number them. Record the test conditions, flow data and test time of the equivalent nozzle to form the standard flow data of the equivalent nozzle.

[0039] 4. Combined with various typical environmental conditions, low pressure, low temperature, and air pressure environmental conditions close to standard conditions, correct the standard flow data of the equivalent nozzle.

[0040] 5. Connect the equivalent nozzle to the air flow test system that needs to be tested, adjust the test pressure condition to the design value, and conduct an air flow test.

[0041] 6. Convert the real-time air flow of the equivalent nozzle under the test condition into the air flow under standard conditions, compare it with the standard flow data under standard conditions, and analyze the flow accuracy of the air flow test system.

[0042] Combination Figure 1 , according to Figure 2, the equivalent nozzle is processed, and no reverse platform is allowed in the channel along the airflow direction. On the high-precision air flow table, when the equivalent nozzle inlet position reaches the specified pressure, the real-time mass flow and test environmental conditions of each working condition are recorded.

[0043] Combination Figure 1The airflow at the designated inlet position is converted between two working conditions with large differences under specified pressure, and the applicability of the conversion formula is calculated through relative deviation calculation.

[0044] Combination Figure 3 , the high-precision air flow test system measures the real-time flow rate under equivalent nozzle working conditions and converts the real-time flow rate into the standard condition flow rate:

[0045] Combination Figure 1 , Figure 3 Screen the equivalent nozzle, the pressure (gauge pressure) at the specified inlet position is △P, the air flow temperature is T2, and its real-time mass flow rate is tested at high and low atmospheric pressures. Through correction, the standard flow data of the equivalent nozzle under standard conditions with higher accuracy is obtained.

[0046] The conversion formula for the standard mass flow rate of dry air is:

[0047] G s =G c α

[0048]

[0049] P1=△P+P0, P2=△P+101.325;

[0050] Where α is the air mass flow conversion coefficient;

[0051] △P is the equivalent nozzle inlet air pressure (gauge pressure), kPa;

[0052] P0 is the ambient atmospheric pressure, kPa;

[0053] P1 is the equivalent nozzle inlet absolute pressure, kPa;

[0054] P2 is the inlet absolute pressure of the equivalent nozzle under standard conditions, kPa;

[0055] T1 is the temperature of the airflow passing through the equivalent nozzle, K;

[0056] T2 is the temperature of the airflow flowing through the equivalent nozzle under standard conditions, K;

[0057] G c is the real-time mass flow rate of the equivalent nozzle, kg / h;

[0058] G S is the standard mass flow rate after conversion of the equivalent nozzle, kg / h.

[0059] Combined with the actual situation of the air flow system, the mass flow accuracy (accuracy) level of the high-precision flow test system should not be less than 0.3. In order to comply with the metrological performance requirements of the national metrology standard specification for closed pipe measurement value transfer "JJG 643-2024 Standard Meter Method Flow Standard Device", the repeatability of the screened equivalent nozzle flow should be ≤0.10%.

[0060] In order to make the standard flow data of the equivalent nozzle more accurate, the pressure measurement point is strictly controlled to be close to the inlet position of the equivalent nozzle, and the air flow temperature is required to be stable. The temperature accuracy is not less than level 1, and the accuracy of the equivalent nozzle inlet pressure (gauge pressure) and atmospheric pressure (absolute pressure) is not less than level 0.1: the air flow temperature is accurate to within 0.5℃, and the pressure is accurate to within 0.5kPa. After the equivalent nozzle inlet pressure is stable, the equivalent nozzle whose flow repeatability meets the above standards is screened to obtain the equivalent nozzle standard flow G S标准 data.

[0061] Combination Figure 4 , the real-time flow rate of the equivalent nozzle working condition is tested on the air flow test system, and the real-time flow rate is converted into the standard condition flow rate.

[0062] Combination Figure 1 The air flow test system tested tests the real-time flow of the equivalent nozzle, and calculates the relative error between the converted standard condition flow and the equivalent nozzle standard flow.

[0063] The inlet diameter of the equivalent nozzle is allowed to be appropriately increased according to the size of the gas nozzle. The size of the throttle hole is calculated according to the converted standard flow rate. The length of the downstream channel of the throttle hole can be appropriately shortened compared with the gas nozzle, and the channel diameter can be appropriately increased. Along the airflow direction, the airflow channel is not allowed to have a reverse platform, and the surface roughness of the airflow channel is not lower than the requirements of the corresponding channel of the gas nozzle. The linear expansion coefficient of the equivalent nozzle material is extremely small, and the size of the throttle hole is minimally affected by the change of airflow temperature.

[0064] When the local atmospheric pressure of the test bench is low, the equivalent nozzle inlet absolute pressure P1 is low. The pressure value is adjusted according to the upper limit of the designed inlet pressure (gauge pressure) to make the difference between the equivalent nozzle inlet absolute pressure P1 and the equivalent nozzle inlet absolute pressure P2 under standard conditions smaller, thereby reducing the influence of atmospheric pressure on the standard condition converted flow rate.

[0065] Example 1

[0066] Combination Figure 1 , Figure 2, determine the equivalent nozzle structure size and process the equivalent nozzle.

[0067] Combination Figure 3The process of measuring and screening the equivalent nozzle standard flow data is carried out in a high-precision air flow test system. The flow standard used for the flow table calibration has obtained a calibration certificate issued by the China Institute of Metrology, certificate number RGll2024-07541. The mass flow accuracy of the air measurement system is better than ±0.3%. The temperature sensor accuracy in the test system is ±0.1℃, and the pressure (gauge pressure) and atmospheric pressure (absolute pressure) accuracy are 0.02%.

[0068] Combination Figure 1 , Figure 3 According to the above air mass flow conversion formula, the equivalent nozzle converts the flow rate from working condition 1 (air flow temperature 306.20K, inlet pressure (gauge pressure) 100.50kPa, atmospheric pressure 95.72kPa) to working condition 2 (air flow temperature 284.45K, equivalent nozzle inlet pressure (gauge pressure) 98kPa, atmospheric pressure 98.02kPa). The converted flow rate is 12.70kg / h, while the real-time flow rate of working condition 2 is 12.69kg / h. The relative error between the two is 0.07%. The conversion formula meets the applicability requirements.

[0069] Combination Figure 1 Figure 2 Figure 3 , the standard flow data of the screened equivalent nozzles: the converted standard air mass flow G S标准 It is 12.85kg / h, and the mass flow repeatability is 0.036%.

[0070] Combination Figure 1 Figure 2 Figure 3 At the air flow temperature T2, according to the absolute pressure before the equivalent nozzle P2 = △P + 101.325, the equivalent nozzle standard flow G selected is corrected according to the real-time flow (theoretical value) S标准 It is 12.86kg / h.

[0071] Combination Figure 4 The mass flow meter range of the air flow test bench being tested is 20kg / h, and the air mass flow accuracy level is 0.5; the temperature sensor range is 0-100℃, and the accuracy level is 0.5; the pressure gauge range is 0-0.16MPa, and the accuracy level is 0.075.

[0072] Combination Figure 4 , compressed air is introduced into the air flow system to be tested, equivalent nozzle inlet pressure (gauge pressure)

[0073] Adjust △P to within the design pressure range and check the air tightness of the pipeline. No leakage is allowed.

[0074] Combination Figure 4When the pressure at the inlet of the equivalent nozzle is stable, keep the pressure for at least 3 minutes. After the flow value is stable, record the test data: air flow temperature 300.35K, ambient atmospheric pressure 98.3kPa, three times average real-time flow 12.45kg / h. Average converted standard flow G S In this embodiment, the equivalent nozzle standard flow rate G S标准 The mass flow rate accuracy (relative error) of the test system is 12.86 kg / h. S -G S标准 ∣ / G S标准 It is 0.30%.

[0075] Example 2

[0076] Example 2 is a variation of Example 1

[0077] Combination Figure 1 , Figure 2 and Figure 3 , the standard flow data of the screened equivalent nozzles: the corrected standard flow G S标准 It is 12.86kg / h, and the mass flow repeatability is 0.036%.

[0078] Combination Figure 4 The mass flow meter range of the air flow test bench being tested is 100kg / h, and the flow accuracy level is 0.5; the temperature sensor range is 0-100℃, and the accuracy level is 0.5; the pressure sensor range is 0-0.40MPa, and the accuracy level is 0.1.

[0079] Combination Figure 4 , the air flow system to be tested is introduced with compressed air, and the equivalent nozzle inlet pressure (gauge pressure) △P is adjusted to the upper limit of the design pressure, so that the difference between the equivalent nozzle inlet absolute pressure P1 and the equivalent nozzle inlet absolute pressure P2 under the standard condition is reduced. And check the air tightness of the pipeline, and no leakage is allowed.

[0080] Combination Figure 4 When the pressure at the inlet of the equivalent nozzle is stable, keep the pressure for at least 3 minutes. After the real-time flow value is stable, record the test data. The air flow temperature is 298.75K, the ambient atmospheric pressure is 93.63kPa, and the average real-time flow rate for three times is 12.12kg / h. Average converted standard flow rate G S In this embodiment, the equivalent nozzle standard flow rate G S标准 The mass flow rate accuracy (relative error) of the test system is 12.86 kg / h. S -G S标准 ∣ / G S标准 It is 0.23%.

[0081] Studies have shown that low temperature has a certain impact on the airflow outflow coefficient. In order to eliminate the temperature effect, the air flow test system should generally ensure that the air flow temperature is not lower than 283.15K during testing.

[0082] Judging from the actual situation of each air flow test bench, high-precision and repeatable measuring instruments are often selected, and effective flow stabilization measures are adopted to ensure the accuracy and stability of the air flow test system.

Claims

1. An equivalent nozzle detection method for air flow measurement system accuracy detection, characterized by: The steps include: (1) In a calibrated high-precision flow test system, screen equivalent nozzles that meet the accuracy and repeatability indicators; (2) Select a reduced flow rate formula with a relatively small error to eliminate the influence of ambient atmospheric pressure and air flow temperature conditions on the reduced flow rate; (3) Screen out equivalent nozzles whose converted standard flow rate is consistent with the designed flow rate of the gas nozzle and number them; record the test conditions, flow data and test time of the equivalent nozzles, thereby forming the standard flow data of the equivalent nozzles; (4) Combine various typical environmental conditions, such as low pressure, low temperature, and air pressure close to standard conditions, to correct the standard flow data of the equivalent nozzle; (5) Connect the equivalent nozzle to the air flow test system to be tested, adjust the test pressure condition to the design value, and perform the air flow test; (6) The real-time air flow rate of the equivalent nozzle under the test condition is converted into the air flow rate under standard conditions, and compared with the standard flow data under standard conditions to analyze the flow accuracy of the air flow test system.

2. The equivalent nozzle detection method for air flow measurement system accuracy detection according to claim 1 is characterized in that: In step (1), the flow accuracy level of the high-precision flow test system is not less than 0.3, and the flow repeatability is ≤0.10%.

3. The equivalent nozzle detection method for air flow measurement system accuracy detection according to claim 1 is characterized in that: The conversion flow rate formula in step (2) is determined based on the engineering fluid mechanics formula combined with test data, and the working fluid is dry air that does not require humidity correction; The standard mass flow conversion formula is: G S =G c ·a P1=△P+P0, P2=△P+101.325; Where α is the mass flow conversion coefficient; △P is the gauge pressure of the air inlet of the equivalent nozzle; P0 is the ambient atmospheric pressure; P1 is the absolute pressure of the inlet of the equivalent nozzle; P2 is the absolute pressure of the inlet of the equivalent nozzle under standard conditions; T1 is the temperature of the airflow flowing through the equivalent nozzle; T2 is the temperature of the airflow flowing through the equivalent nozzle under standard conditions; G c is the real-time mass flow rate of the equivalent nozzle; G S It is the standard mass flow rate after conversion of the equivalent nozzle.

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