A dynamic calibration device for a frequency-adjustable variable cross-section gas flow meter

Abstract

This invention discloses a dynamic calibration device for a frequency-adjustable variable cross-section gas flow meter, belonging to the field of gas flow metering technology. The device includes a variable frequency motor, a rotary valve, a fan, a rectifier, a stabilizing section, a contraction section, a development section, and a testing section connected in sequence. The rotary valve consists of a stator and a rotor; the rotor rotation causes the flow cross-sectional area to change sinusoidally, generating a standard sinusoidal flow signal. The variable frequency motor is used to adjust the rotor speed, achieving precise control of the signal frequency. The fan provides suction power. The rectifier, stabilizing, contraction, and development sections are used to ensure the airflow reaches a fully developed laminar flow state. The testing section measures the pressure gradient using a dynamic pressure sensor. This invention also provides a method for obtaining a standard volumetric flow signal by solving the analytical solution of the Navier-Stokes equations based on the pressure gradient. This device solves the problems of difficulty in controlling the generation of dynamic flow signals and the difficulty in directly tracing the source of standard flow, achieving high-precision calibration of the dynamic characteristics of the gas flow meter.

Description

Technical Field

[0001] This invention belongs to the field of gas flow meter calibration technology, specifically relating to a dynamic calibration device for a frequency-adjustable variable cross-section gas flow meter. Background Technology

[0002] Gas flow metering is a key foundational technology in energy trade, industrial production, environmental monitoring, and high-end manufacturing. With the increasing demands for process control accuracy and transient response from advanced industries such as semiconductor manufacturing, biomedicine, and fine chemicals, stringent requirements are being placed on the measurement performance of gas flow meters in dynamic and periodically changing flow fields. Accordingly, dynamic calibration—that is, establishing an accurate response relationship under varying flow rates—has become a core problem urgently needing to be solved in the field of flow metering.

[0003] Currently, gas flow calibration technology can be divided into two categories: steady-state calibration and dynamic calibration. For steady-state calibration, the technology is quite mature, with a complete system and national standards represented by bell-type, sonic nozzle, and standard meter methods. These devices can provide high-precision constant flow rates, but they cannot evaluate the dynamic characteristics of the flow meter.

[0004] For dynamic calibration, existing technical solutions have significant limitations and cannot meet the requirements of high precision, wide bandwidth, and standardization: Dynamic flow signals are difficult to generate and of poor quality: Existing solutions are mostly based on the periodic opening and closing of mechanical valves (such as solenoid valves and butterfly valves) or the modulation of fan speed. The former produces flow waveforms that are square waves or trapezoidal waves, containing a large number of high-order harmonics, and are not ideal single-frequency sinusoidal excitations, making them unsuitable for accurate analysis of frequency response characteristics; the latter, due to the large inertia of the fan and drive system, has a slow response and makes it difficult to generate high-frequency (usually below 1Hz) and pure periodic signals.

[0005] Standard dynamic flow rate values ​​are difficult to trace and obtain: The compressibility of gases and the nonlinear characteristics of flow make it extremely difficult to directly and accurately measure instantaneous flow rates in pulsating flow. Traditional methods often connect a steady-state calibration device (such as a sonic nozzle) in series with a dynamic flow generator, attempting to use the steady-state value as a reference. However, establishing a dynamic flow field changes the operating conditions of the upstream steady-state device, introducing systematic errors that are difficult to quantify, leading to increased uncertainty in the "standard" flow rate value itself, and making true dynamic traceability impossible.

[0006] The contradiction between device complexity and controllability: Some devices designed to generate high-quality pulsating flow (such as volumetric sources based on piston actuators) are complex in structure, expensive, and difficult to independently adjust in terms of frequency and amplitude, making them difficult to integrate into practical calibration systems.

[0007] In summary, the core bottleneck of current dynamic calibration technology for gas flow meters lies in the lack of a device capable of generating a dynamic flow signal with adjustable frequency and a standard (sine) waveform, and simultaneously and with high precision acquiring this dynamic standard flow value. This directly restricts the evaluation and improvement of the dynamic performance of high-end gas flow meters. Summary of the Invention

[0008] The technical problem to be solved: To overcome the shortcomings of existing technologies, this invention provides a dynamic calibration device for a frequency-adjustable variable cross-section gas flow meter. It generates a periodic sinusoidal flow signal by periodically changing the pipe cross-sectional area; adjusts the flow signal frequency by regulating the motor speed; and obtains a standard flow signal by measuring the pressure gradient and solving the Navier-Stokes equations under periodic pulsating pressure conditions within the pipe. From signal generation, rectification, stabilization, and development to testing, a complete dynamic calibration system is formed. This solves the problems of difficulty in controlling the generation of periodic dynamic flow signals, low generation frequency, and difficulty in obtaining standard flow signals in existing technologies.

[0009] The technical solution of this invention is: a dynamic calibration device for a frequency-adjustable variable cross-section gas flow meter, comprising: A periodic variable cross-section flow signal generation unit is used to generate flow signals in a flow channel in which the flow rate, velocity, and pressure change periodically over time. A flow field conditioning unit, connected downstream of the signal generating unit, is used to rectify, stabilize, and accelerate the flow from the signal generating unit, and to develop the airflow into a fully developed laminar flow state before entering the test area. A standard signal acquisition unit is set in the test area where the airflow is fully developed in the flow field adjustment unit, and is used to measure the dynamic pressure gradient of the flow field; The flow signal frequency is adjusted by regulating the periodic variation frequency of the periodic variable cross-section flow signal generating unit; the standard volumetric flow signal, which serves as the calibration reference, is obtained by combining the dynamic pressure gradient measured by the standard signal acquisition unit with the pulsating flow theory model.

[0010] A further technical solution of the present invention is: the periodic variable cross-section flow signal generating unit includes a variable frequency motor 1 and a rotary valve 2; The rotary valve is composed of a stator 21 and a rotor 22 arranged coaxially. The rotor 22 rotates relative to the stator 21 under the drive of the variable frequency motor 1. The stator 21 and rotor 22 are provided with mutually cooperating flow windows. When the rotor 22 rotates, the overlapping flow area of ​​the flow windows changes periodically, thereby generating a periodically changing flow signal.

[0011] A further technical solution of the present invention is: in the rotary valve 2, the stator 21 and the rotor 22 adopt a coaxial sleeve-type fitting structure; The stator 21 is a fixed outer sleeve, and a stator flow window is provided on its end face; the stator flow window is composed of four fan-shaped holes arranged in a circumferential array, with the small radius of the fan ring being r1, the large radius being r2, and the central angle being 2θ; The rotor 22 is a rotating inner sleeve placed inside the stator 21, and a rotor flow window is provided on its end face; the rotor flow window is composed of four circular holes arranged in a circumferential array with a radius of r; The structural design of the stator 21 and rotor 22 satisfies , , This causes the overlapping circulation area to change sinusoidally over time; among which, L denoted as , which is the distance between any circular hole on the rotor and the center of the rotor.

[0012] A further technical solution of the present invention is: the flow field adjustment unit comprises, in sequence along the airflow direction: Fan 3 is used to provide suction power for the device; The rectifier 4 is located downstream of the fan 3 and has a honeycomb structure inside to reduce the turbulence of the airflow. The stabilizing section 5 is connected downstream of the rectifier 4, providing a stable and uniform flow path for the airflow. The contraction section 6, connected downstream of the stabilization section 5, is used to accelerate the airflow; Development section 7, connected downstream of contraction section 6, is long enough to allow the airflow to develop into a fully developed laminar flow before reaching the downstream test area.

[0013] A further technical solution of the present invention is: the honeycomb structure of the rectifier 4 has a hexagonal cross section, and the ratio of the honeycomb length L to the honeycomb aperture diameter M is 5; the length of the stabilizing section 5 is 5 times its diameter; the contraction curve of the contraction section 6 is defined by the Vickers curve, and the ratio of its inlet cross-sectional area to its outlet cross-sectional area is 18. A further technical solution of the present invention is: the standard signal acquisition unit is a test section 8 located downstream of the development section 7; a plurality of pressure measuring holes 81 are provided on the pipe wall of the test section 8 along the axial direction at a predetermined interval for installing dynamic pressure sensors to measure the pressure gradient along the pipe.

[0014] A further technical solution of the present invention is that the installation method of the pressure measuring hole 81 ensures that the plane where the sensor air guide hole is located is tangent to the inner wall of the pipe.

[0015] A further technical solution of the present invention is as follows: the rotor 22 has a short shaft at its center and a bearing is installed thereon; the stator 21 has a circular hole at its center that mates with the bearing, so as to constrain the radial movement of the rotor 22; the radius of the rotor 22 is slightly smaller than the radius of the stator 21, and there is an operating clearance between them; the components of the signal generation unit and the flow field adjustment unit are ensured to be coaxially installed. A method for acquiring a dynamic gas flow rate standard signal based on the aforementioned device includes the following steps: Step 1: Start the device to generate a periodic flow signal through the periodic variable cross-section flow signal generating unit; Step 2: After passing through the flow field conditioning unit, the airflow forms a fully developed laminar pulsating flow in the test area; Step 3: The axial pressure gradient of the pulsating flow is measured using the standard signal acquisition unit, and its expression is:

[0016] in, air density, The steady-state component amplitude of the pressure. The amplitude of the sinusoidal pressure pulsation. The frequency of the sinusoidal signal; Step 4: Based on the theoretical model of fully developed laminar flow pulsation in a circular pipe, the pressure gradient is correlated with the standard volumetric flow rate, and the standard volumetric flow rate signal is calculated using the following formula:

[0017] in, P M The steady-state component amplitude of the pressure. P A The amplitude of the sinusoidal pressure pulsation. f The frequency of the sinusoidal signal. R For the pipe radius, v The viscosity is the kinematic viscosity of air.

[0018] A further technical solution of the present invention is: in step 4, the function Defined as:

[0019] in, , For the pipe radius, The viscosity of air motion. i The imaginary unit, J 0 represents a Bessel function of the first kind of order 0. J 1 represents a first-order Bessel function of the first kind.

[0020] Beneficial effects The beneficial effects of this invention are as follows: This invention achieves stable and controllable generation of periodic sinusoidal flow signals by periodically changing the pipe cross-sectional area; it adjusts the flow signal frequency by regulating the motor speed; and it obtains a standard flow signal by measuring the pressure gradient and solving the Navier-Stokes equations under periodic pulsating pressure conditions within the pipe. This solves the problems of difficulty in controlling the generation of periodic dynamic flow signals, low generation frequency, and difficulty in obtaining standard flow signals in existing technologies. Specific effects are as follows: 1. This invention, through a "rotary valve" design, enables the flow cross-sectional area to continuously change according to a precise sinusoidal law, generating theoretically pure, high-quality single-frequency sinusoidal flow and pressure signals from the source. This completely overcomes the problems of impure square waves, trapezoidal waves, or slow-responding signals with high harmonic content generated by traditional methods such as solenoid valves or adjusting fan speed, providing an ideal excitation source for the accurate calibration of the flow meter's frequency response characteristics and other dynamic performance.

[0021] 2. This invention employs a variable frequency motor to directly drive the rotary valve, allowing for linear and continuous adjustment of the frequency of the sinusoidal flow signal by changing the motor speed. This method offers fast response and high control precision, achieving a wider frequency adjustment range than traditional methods that adjust fan speed or piston actuators. Furthermore, the frequency adjustment is independent of the flow amplitude, making operation flexible and convenient.

[0022] 3. This invention abandons the traditional approach of tracing dynamic flow to steady-state standards indirectly and with large errors. It innovatively employs dynamic pressure gradient measurement combined with analytical solutions to the Navier-Stokes equations to directly obtain the time-domain signal of the standard volumetric flow rate as a calibration benchmark. This method is theoretically rigorous, does not rely on any external steady-state flow standard device, and achieves direct, theoretical tracing of dynamic quantities, fundamentally solving the core bottleneck of "difficulty in obtaining and unreliability" of dynamic standard flow rates.

[0023] 4. This invention, by systematically integrating a flow field regulation unit consisting of a "rectifier—stabilization section—contraction section—long development section," ensures that the airflow reaches a fully developed laminar flow state before entering the test section. This highly uniform and stable flow field condition is a prerequisite for the strict validity of the analytical solution of the aforementioned Navier-Stokes equations, thus guaranteeing the theoretical accuracy and practical reliability of the calculation from pressure gradient to standard flow rate, which cannot be provided by ordinary wind tunnels or simple pipes. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the overall structure of the frequency-adjustable variable cross-section gas flow meter dynamic calibration device in an embodiment of the present invention. Figure 2 This is a schematic diagram of the rotary valve geometry in an embodiment of the present invention; Figure 3 This is a schematic diagram of the rectifier device structure in an embodiment of the present invention; Figure 4 This is a schematic diagram of the stable section structure in an embodiment of the present invention; Figure 5 This is a schematic diagram of the contraction section structure in an embodiment of the present invention; Figure 6 This is a schematic diagram of the development segment structure in an embodiment of the present invention; Figure 7 This is a schematic diagram of the test segment structure in an embodiment of the present invention; Figure 8 The image shown is a physical representation of an embodiment of the present invention. Figure 9 This is a diagram showing the experimental results with a signal frequency of 7Hz in an embodiment of the present invention; Figure 10 This is a diagram showing the experimental results with a signal frequency of 42Hz in an embodiment of the present invention. Figure 9 and Figure 10 The black line represents the measured pressure gradient, and the red line represents the flow rate calculated from the pressure gradient using theoretical formulas.

[0025] Explanation of reference numerals in the attached drawings: 1. Motor; 2. Rotary valve; 21. Stator; 22. Rotor; 3. Fan; 4. Rectifier; 5. Stabilizing section; 6. Contraction section; 7. Development section; 8. Testing section; 81. Pressure testing hole; 9. Coupling. Detailed Implementation

[0026] The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the invention, and should not be construed as limiting the invention.

[0027] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0028] Flow measurement, as an important component of thermal metering, plays a vital role in the development of human civilization. With the continuous development of society, the theory of flow measurement has been initially perfected and has been applied to all aspects of industrial production and people's daily lives. Flow measurement is indispensable in ubiquitous household appliances such as electricity meters, water meters, and gas meters, as well as in national natural gas metering, international oil trade, and the testing of various devices in aerospace.

[0029] In recent years, the semiconductor manufacturing, fine chemical, and biomedicine industries have developed rapidly. These fields have increasingly stringent requirements for measurement accuracy and transient response, making the need for dynamic gas flow measurement increasingly urgent. Gas flow meters are instruments that measure directly in the field, and their measurement accuracy is closely related to scientific research and metrological benefits. However, gas flow meters need to be calibrated before use to establish the relationship between the measured value and the standard value. Therefore, the research on gas flow meter calibration devices is extremely necessary.

[0030] For steady-state devices, a great deal of work has been done, and a complete theoretical system has been formed. For dynamic devices, due to the strong compressibility and high nonlinearity of gases, a complete theoretical system has not yet been formed at home and abroad, and they face problems such as difficulty in controllable generation, low generation frequency, and difficulty in obtaining standard flow signals.

[0031] To address the aforementioned problems, this invention proposes a dynamic calibration device for a frequency-adjustable variable cross-section gas flow meter, comprising: A periodic variable cross-section flow signal generation unit is used to generate flow signals in a flow channel in which the flow rate, velocity, and pressure change periodically over time. A flow field conditioning unit, connected downstream of the signal generating unit, is used to rectify, stabilize, and accelerate the flow from the signal generating unit, and to develop the airflow into a fully developed laminar flow state before entering the test area. A standard signal acquisition unit is set in the test area where the airflow is fully developed in the flow field adjustment unit, and is used to measure the dynamic pressure gradient of the flow field; The flow signal frequency is adjusted by regulating the periodic variation frequency of the periodic variable cross-section flow signal generating unit; the standard volumetric flow signal, which serves as the calibration reference, is obtained by combining the dynamic pressure gradient measured by the standard signal acquisition unit with the pulsating flow theory model.

[0032] The above technical solution will be further analyzed below with examples and accompanying figures: Example 1: Specific implementation of the device structure.

[0033] Reference Figure 1 As shown in the figure, this embodiment proposes a dynamic calibration device for a frequency-adjustable variable cross-section gas flow meter. The device, along the airflow direction, includes, in sequence: a periodic variable cross-section flow signal generation unit (mainly composed of a variable frequency motor 1 and a rotary valve 2), a fan 3, a rectifier 4, a stabilizing section 5, a contraction section 6, a development section 7, and a testing section 8. The rotor 2 in the rotary valve 2 is connected to the motor 1 via a coupling 9. All components are connected by flanges to ensure strict coaxiality, and rubber gaskets are installed at the connections to ensure a seal.

[0034] Reference Figure 2As shown, the rotary valve 2 comprises a stator 21 and a rotor 22, both mounted coaxially. The stator 21 is fixed and has a central hole for mounting a bearing. The rotor 22 rotates under the drive of the variable frequency motor 1 and has a short shaft at its center, which engages with the central hole of the stator 21 via a bearing. This design effectively constrains the radial runout of the rotor 22 and reduces rotational vibration. To avoid friction, the outer radius of the rotor 22 is slightly smaller than the inner radius of the stator 21, with a uniform gap of approximately 0.2 mm between them.

[0035] The stator and rotor structural dimensions satisfy the following geometric relationships: , , .

[0036] Reference Figure 3 As shown, the rectifier 4 is a circular cross-section pipe filled with hexagonal cross-section honeycomb cells. The ratio of the honeycomb length L to the honeycomb aperture diameter M is 5.

[0037] Reference Figure 4 As shown, the stabilizing section 5 is a straight circular pipe of equal diameter located between the rectifier 4 and the contraction section 6. The stabilizing section serves to rectify the airflow, ensuring sufficient time for airflow stabilization, and should also have high sealing performance. In this embodiment, the length Ls of the stabilizing section 5 is five times its diameter Ds (Ls=5Ds) to ensure sufficient airflow stabilization.

[0038] Reference Figure 5 As shown, the contraction section 6 has a circular cross-section, and the ratio of the inlet cross-sectional area to the outlet cross-sectional area (contraction ratio) is 18. The contraction curve is defined by the Vickers curve.

[0039]

[0040] In the formula, The radius of the inlet section of the contraction segment. The radius of the exit section of the contraction section. The axial distance is The radius of the cross section at that location, This is the length of the contraction segment.

[0041] Reference Figure 6 As shown, the length of development segment 7 is estimated using the following formula:

[0042] In the formula: .

[0043] This means that the length of the development section needs to be greater than 100 times the diameter of the development section's circular tube.

[0044] Reference Figure 7As shown, test section 8 is a straight circular pipe with the same diameter as development section 7, serving as a continuation of its airflow. Five pressure measurement holes are opened on it at 10cm intervals for installing dynamic pressure sensors to measure the pressure gradient. During installation, the plane of the air guide hole must be tangent to the inner wall of the pipe.

[0045] Figure 8 A physical diagram of the calibration device is provided. During operation, the fan creates a low-pressure zone through its high-speed rotating blades. Ambient air is drawn into the calibration device after passing through a rotary valve. After rectification by the rectifier, vortex attenuation occurs, and the airflow becomes more uniform. After passing through the stable section, the turbulence intensity further decreases. After acceleration in the contraction section, the airflow enters the development section, allowing it to fully develop. Finally, the pressure gradient is measured by a pressure sensor in the test section. The standard volumetric flow rate signal is obtained by solving the Navier-Stokes equations under periodic pulsating pressure conditions within the pipe. The steady-state flow rate is adjusted by regulating the fan power, and the frequency of the periodic sinusoidal flow rate signal is changed by altering the rotor speed.

[0046] Example 2: Specific implementation of the standard flow signal acquisition method.

[0047] This example provides a method for obtaining the periodic sinusoidal standard volumetric flow rate of a fluid under fully developed laminar flow conditions. The standard volumetric flow rate signal can be obtained by calculating the pressure gradient measured by the aforementioned device. The specific method is as follows: Step 1: Start the device to generate a periodic flow signal through the periodic variable cross-section flow signal generating unit; Step 2: After passing through the flow field conditioning unit, the airflow forms a fully developed laminar pulsating flow in the test area; Step 3: The axial pressure gradient of the pulsating flow is measured using the standard signal acquisition unit, and its expression is:

[0048] in, air density, The steady-state component amplitude of the pressure. The amplitude of the sinusoidal pressure pulsation. The frequency of the sinusoidal signal; Step 4: Based on the theoretical model of fully developed laminar flow pulsation in a circular pipe, the pressure gradient is correlated with the standard volumetric flow rate.

[0049] Define with respect to dimensionless frequency function The formula is:

[0050] In the formula, , For the pipe radius, The viscosity of air motion. i The imaginary unit, J 0 represents a Bessel function of the first kind of order 0. J 1 represents a first-order Bessel function of the first kind.

[0051] The standard volumetric flow rate signal can then be expressed in the following form, using the formula:

[0052] and According to Solve using the formula:

[0053] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention without departing from the principles and spirit of the present invention.

Claims

1. A dynamic calibration device for a frequency-adjustable variable cross-section gas flow meter, characterized in that, include: A periodic variable cross-section flow signal generation unit is used to generate flow signals in a flow channel in which the flow rate, velocity, and pressure change periodically over time. A flow field conditioning unit, connected downstream of the signal generating unit, is used to rectify, stabilize, and accelerate the flow from the signal generating unit, and to develop the airflow into a fully developed laminar flow state before entering the test area. A standard signal acquisition unit is set in the test area where the airflow is fully developed in the flow field adjustment unit, and is used to measure the dynamic pressure gradient of the flow field; The flow signal frequency is adjusted by regulating the periodic variation frequency of the periodic variable cross-section flow signal generating unit; the standard volumetric flow signal, which serves as the calibration reference, is obtained by combining the dynamic pressure gradient measured by the standard signal acquisition unit with the pulsating flow theory model.

2. The frequency-adjustable variable cross-section gas flow meter dynamic calibration device according to claim 1, characterized in that: The periodic variable cross-section flow signal generating unit includes a variable frequency motor (1) and a rotary valve (2); The rotary valve is composed of a stator (21) and a rotor (22) arranged coaxially. The rotor (22) rotates relative to the stator (21) under the drive of the variable frequency motor (1). The stator (21) and rotor (22) are provided with mutually cooperating flow windows. When the rotor (22) rotates, the overlapping flow area of ​​the flow windows changes periodically, thereby generating a periodically changing flow signal.

3. The frequency-adjustable variable cross-section gas flow meter dynamic calibration device according to claim 2, characterized in that: In the rotary valve (2), the stator (21) and the rotor (22) adopt a coaxial sleeve-type fitting structure; The stator (21) is a fixed outer sleeve, and a stator flow window is provided on its end face; the stator flow window is composed of 4 fan-shaped holes arranged in a circumferential array, with the small radius of the fan ring being r1, the large radius being r2, and the central angle being 2θ; The rotor (22) is a rotating inner sleeve placed inside the stator (21), and a rotor flow window is provided on its end face; the rotor flow window is composed of 4 circular holes arranged in a circumferential array with a radius of r; The structural design of the stator (21) and rotor (22) satisfies , , This causes the overlapping circulation area to change sinusoidally over time; among which, L denoted as , which is the distance between any circular hole on the rotor and the center of the rotor.

4. The frequency-adjustable variable cross-section gas flow meter dynamic calibration device according to claim 3, characterized in that: The rotor (22) has a short shaft at its center and a bearing is installed thereon. The stator (21) has a circular hole at its center that mates with the bearing to constrain the radial movement of the rotor (22). The radius of the rotor (22) is slightly smaller than the radius of the stator (21), and there is a running gap between them. The components of the signal generation unit and the flow field adjustment unit are coaxially installed.

5. The frequency-adjustable variable cross-section gas flow meter dynamic calibration device according to claim 1, characterized in that: The flow field adjustment unit comprises, in sequence along the airflow direction: The fan (3) is used to provide suction power for the device; A rectifier (4) is located downstream of the fan (3) and has a honeycomb structure inside to reduce the turbulence of the airflow. The stabilization section (5) is connected downstream of the rectifier (4) to provide a stable and uniform flow path for the airflow. The contraction section (6) is connected downstream of the stabilization section (5) and is used to accelerate the airflow; The development section (7), connected downstream of the contraction section (6), is long enough to allow the airflow to develop into a fully developed laminar flow before reaching the downstream test area.

6. The frequency-adjustable variable cross-section gas flow meter dynamic calibration device according to claim 5, characterized in that: The rectifier (4) has a hexagonal cross-section in its honeycomb structure, and the ratio of the honeycomb length L to the honeycomb aperture diameter M is 5; the length of the stabilizing section (5) is 5 times its diameter; the contraction curve of the contraction section (6) is defined by the Vickers curve, and the ratio of its inlet cross-sectional area to its outlet cross-sectional area is 18.

7. The frequency-adjustable variable cross-section gas flow meter dynamic calibration device according to claim 1, characterized in that: The standard signal acquisition unit is a test section (8) located downstream of the development section (7); multiple pressure measuring holes (81) are provided on the pipe wall of the test section (8) at preset intervals along the axial direction, for installing dynamic pressure sensors to measure the pressure gradient along the pipe.

8. The frequency-adjustable variable cross-section gas flow meter dynamic calibration device according to claim 7, characterized in that: The installation method of the pressure measuring hole (81) ensures that the plane where the sensor air guide hole is located is tangent to the inner wall of the pipe.

9. A method for acquiring a dynamic gas flow rate standard signal based on the device according to any one of claims 1-8, characterized in that, Includes the following steps: Step 1: Start the device to generate a periodic flow signal through the periodic variable cross-section flow signal generating unit; Step 2: After passing through the flow field conditioning unit, the airflow forms a fully developed laminar pulsating flow in the test area; Step 3: The axial pressure gradient of the pulsating flow is measured using the standard signal acquisition unit, and its expression is: in, air density, The steady-state component amplitude of the pressure. The amplitude of the sinusoidal pressure pulsation. The frequency of the sinusoidal signal; Step 4: Based on the theoretical model of fully developed laminar flow pulsation in a circular pipe, the pressure gradient is correlated with the standard volumetric flow rate, and the standard volumetric flow rate signal is calculated using the following formula: in, P M The steady-state component amplitude of the pressure. P A The amplitude of the sinusoidal pressure pulsation. f The frequency of the sinusoidal signal. R For the pipe radius, v The viscosity is the kinematic viscosity of air.

10. The method for acquiring the dynamic gas flow standard signal according to claim 9, characterized in that: In step 4, the function Defined as: in, , For the pipe radius, The viscosity of air motion. i The imaginary unit, J 0 represents a Bessel function of the first kind of order 0. J 1 represents a first-order Bessel function of the first kind.

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