A flow calculation method suitable for multi-channel ultrasonic flowmeter

Abstract

The present invention discloses a flow calculation method applicable to a multi-channel ultrasonic flowmeter, which includes the following steps: calculating the span interval of the flow field Reynolds number R e ; equally dividing the span interval of R e on a logarithmic coordinate axis; building a system model measured by the ultrasonic flowmeter and setting boundary conditions for numerical simulation calculation; performing numerical calculations for each operating point, and obtaining flow field data after the calculation converges; determining the channel positions and weighting values of the multi-channel ultrasonic flowmeter, and calculating the axial average flow velocity; calculating the average sound velocity along the channel line; obtaining the average sound velocity of the multi-channel ultrasonic flowmeter on each channel line; and obtaining the measured axial average flow velocity under each operating condition; obtaining the actual axial average flow velocity of each operating condition; calculating the deviation between the measured average axial flow velocity and the actual average axial flow velocity under each operating condition, and averaging to obtain the average measurement deviation; performing velocity profile correction on the measured value in the multi-channel ultrasonic flowmeter; and obtaining the average axial flow velocity.

Description

Technical Field

[0001] The invention belongs to the technical field of flow measurement, and in particular relates to a flow calculation method suitable for a multi-channel ultrasonic flowmeter. Background Art

[0002] The time difference ultrasonic flow meter is a mainstream flow measurement device on the market. It calculates the flow rate of the fluid by measuring the time difference between the ultrasonic wave propagating in the downstream and upstream processes. Figure 1 As shown, the average flow velocity in the tube is V, the inner diameter of the tube is D, the angle between the center line of the two transducers and the flow direction is φ, and the length of the sound channel is L (the sound channel refers to the actual path for the ultrasonic signal to propagate between the paired ultrasonic transducers).

[0003] The actual propagation speed of sound waves in the fluid is determined by the propagation speed of sound waves in the static state of the medium c f and the component of the average axial velocity V of the fluid in the direction of sound wave propagation. The propagation time of sound waves in the downstream and upstream can be expressed as:

[0004]

[0005]

[0006] Where, t d is the time for the ultrasonic wave to propagate downstream in the fluid; t u It is the time for the ultrasonic wave to propagate in the countercurrent of the fluid.

[0007] By solving the above two equations together, we can get the expression of the average axial velocity of the fluid in the tube:

[0008]

[0009] The relationship between the average axial velocity of the fluid in the tube and the average axial velocity of the measured sound channel is established through ideal flow field conditions, and then multiplied by the cross-sectional area of ​​the fluid, the fluid volume flow rate can be obtained, as shown in the following formula:

[0010] q v =VA

[0011] In the formula, q v is the volume flow rate; A is the fluid cross-sectional area.

[0012] The above is the measurement principle of a single-channel ultrasonic flowmeter. A single-channel flowmeter has only one channel velocity and is more sensitive to changes in flow conditions. In order to improve the measurement accuracy of the ultrasonic flowmeter, multiple channels are arranged in parallel on the section to be measured. The channel velocity obtained can represent the average velocity in the corresponding parallel strips on the section to be measured. For circular pipe sections, the Gauss-Legendre integration method is used to calculate the flow in a circular pipe, such as Figure 2As shown, the following formula is the volume flow calculation formula.

[0013]

[0014] Where n is the number of channels; W i is the weighting coefficient on channel i; x i For r i / R;V i is the average axial velocity on channel i.

[0015] When the number of channels n is determined, there is an optimal set of W i 、x i Value makes q v The calculation accuracy is maximized.

[0016] The above is the measurement principle of the current mainstream multi-channel time-difference ultrasonic flowmeter.

[0017] For multi-channel ultrasonic flowmeters, the numerical integration method is used to solve the flow rate, and the volume flow rate is solved by using the weighted summation method of a finite number of channels. This method is a universal calculation method and does not consider the impact of the change in the velocity profile of the fluid in the pipe on the calculation results. Figure 3 As shown in the figure, when the flow field conditions (such as Reynolds number) vary within a large range, the velocity profile of the fluid in the pipe will be deformed, or the conditions of the upstream pipe section of the measurement position are poor, the straight pipe section conditions are insufficient, and the velocity profile is asymmetrically arranged, all of which will affect the measurement accuracy. Summary of the invention

[0018] In view of this, in order to overcome the defects of the prior art, an object of the present invention is to provide a flow calculation method suitable for a multi-channel ultrasonic flowmeter.

[0019] In order to achieve the above object, the present invention adopts the following technical solutions:

[0020] A flow calculation method applicable to a multi-channel ultrasonic flowmeter comprises the following steps:

[0021] 1) According to the use requirements and equipment parameters of the multi-channel ultrasonic flowmeter, confirm the layout of the upstream and downstream pipe sections at the measurement location, including the length of the straight pipe, the number of elbows, the elbow structure, whether there are valves, whether there are diameter changes, etc.; confirm the pipe diameter and wall roughness between the ultrasonic transducers; confirm the range of changes in the fluid parameters in the pipeline;

[0022] 2) Calculate the Reynolds number R of the flow field according to the variation range of the fluid parameters in the pipeline e The span interval [R e min , R e max ];

[0023] 3) R eThe span interval is equally divided on the logarithmic coordinate axis to obtain n Reynolds number nodes, n ≥ 7, and m flow field operating points are designed for each Reynolds number through different flow, temperature, and pressure combinations, m ≥ 3;

[0024] 4) Build a system model measured by the ultrasonic flowmeter in the numerical simulation software and set the boundary conditions for the numerical simulation calculation;

[0025] 5) Based on the system model in step 4), numerical calculation is performed on each operating point, and flow field data is obtained after the calculation converges;

[0026] 6) The Gauss-Legendre numerical integration method is used to determine the channel position and weighting value of the multi-channel ultrasonic flowmeter, and the axial average flow velocity is calculated;

[0027] 7) deriving the coordinate parameters and velocity coordinate parameters of each sound channel line in the coordinate axis, and calculating the average sound velocity along the sound channel line;

[0028] 8) Repeat step 7) for each other channel parameter to find the average sound velocity of the multi-channel ultrasonic flowmeter on each channel line; and repeat step 6) to obtain the measured axial average flow velocity V under each working condition. measure ;

[0029] 9) The axial average flow velocity on the middle section of the transducer is taken as the theoretical true value, and the actual axial average flow velocity V of each working condition is obtained by the integration method. acutal ;

[0030] 10) Calculate the deviation between the measured average axial flow velocity and the actual average axial flow velocity under each working condition;

[0031] 11) averaging the measurement deviations under various Reynolds number conditions to obtain an average measurement deviation;

[0032] 12) Perform polynomial fitting on the average measurement deviation and Reynolds number to obtain a fitting formula; perform velocity profile correction on the measured value in the multi-channel ultrasonic flowmeter, and the correction coefficient is:

[0033]

[0034] In the formula, K σ is the correction coefficient, σ' is the average measurement deviation;

[0035] 13) Correct the measured average axial velocity according to the correction factor.

[0036] According to some preferred implementation aspects of the present invention, the fluid parameters in step 1) include flow rate, pressure, and temperature.

[0037] According to some preferred embodiments of the present invention, the flow field Reynolds number R in step 2)e Calculated by the following formula:

[0038]

[0039] Where ρ is the fluid density; V is the average axial velocity in the pipe; d is the pipe diameter; and μ is the kinematic viscosity of the fluid.

[0040] According to some preferred implementation aspects of the present invention, the modeling range of the system model in step 4) is based on the ultrasonic flow meter measurement point, with the upstream pipeline being at least 50D and the downstream pipeline being at least 20D.

[0041] According to some preferred implementation aspects of the present invention, the boundary conditions in step 4) use the volume flow rate, fluid temperature, and fluid pressure under various operating conditions in step 3) as boundary conditions for numerical calculation.

[0042] According to some preferred implementation aspects of the present invention, the axial average flow velocity in step 6) is calculated by the following formula:

[0043]

[0044] Where V measure is the average axial velocity, V i is the average speed of sound along the sound channel, x i is the channel position of the multi-channel ultrasonic flowmeter, w i It is the weighted value of the channel position of the multi-channel ultrasonic flowmeter.

[0045] According to some preferred implementation aspects of the present invention, the average sound speed along the sound channel line in step 7) is calculated by the following steps:

[0046] 1) Set the position coordinates of a point R on the AB channel in the x, y coordinate system to (L Rx , L Ry ), the velocity coordinate is (V Rx , V Ry );

[0047] 2) A(L Ax , L Ay ) is used as the origin to establish a single-axis coordinate system in the AB direction. The position coordinate of point R is the distance relative to point A. The speed value is The position and velocity coordinates of R are

[0048] 3) Calculate the average speed of sound along the sound channel line using the following formula:

[0049]

[0050] Where V AB is the average speed of sound along the sound channel, L A is the position coordinate of point A, L B is the position coordinate of point B.

[0051] According to some preferred implementation aspects of the present invention, the measurement deviation σ in step 10) is calculated by the following formula:

[0052]

[0053] Where σ is the measurement deviation; V measure is the average axial velocity; V acutal is the actual average axial velocity.

[0054] According to some preferred implementation aspects of the present invention, the average axial flow velocity measured by correction of the correction coefficient is:

[0055]

[0056] Where V is the corrected average axial velocity.

[0057] Due to the adoption of the above technical scheme, compared with the prior art, the advantages of the present invention are: the flow calculation method of the present invention, which is suitable for a multi-channel ultrasonic flowmeter, can eliminate the measurement error caused by the uneven pipeline flow field and the deformation of the velocity profile with the Reynolds number by introducing a correction coefficient of the velocity profile; it is used to compensate for the influence of the velocity profile changing with the Reynolds number on the measurement accuracy, and ensure that the ultrasonic flowmeter has stable measurement accuracy under a large range of Reynolds number changes in specific application scenarios (upstream and downstream pipe section layout, pipe section roughness, etc.). BRIEF DESCRIPTION OF THE DRAWINGS

[0058] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0059] Figure 1 It is a measurement schematic diagram of a time difference method ultrasonic flowmeter in the prior art;

[0060] Figure 2 It is a schematic diagram of the measurement principle of a multi-channel ultrasonic flowmeter in the prior art;

[0061] Figure 3 is the velocity profile under different Reynolds number conditions;

[0062] Figure 4It is a schematic diagram of the measurement of four channels in an embodiment of the present invention. DETAILED DESCRIPTION

[0063] In order to enable those skilled in the art to better understand the technical solution of the present invention, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0064] like Figure 4 As shown, the process of generating the velocity profile correction coefficient for an ultrasonic flow meter with four sound channels in a specific application scenario in this embodiment includes the following steps, wherein the specific application scenario refers to the flow meter being installed at a fixed position on the pipeline, and the upstream and downstream pipeline layouts are fixed.

[0065] 1. According to the use requirements and equipment parameters of the multi-channel ultrasonic flowmeter, confirm the layout of the upstream and downstream pipe sections at the measurement location, including the length of the straight pipe, the number of elbows, the elbow structure, whether there are valves, whether there are reducers, etc.; confirm the pipe diameter and wall roughness between the ultrasonic transducers; confirm the range of changes in the fluid parameters in the pipeline, including flow, pressure, and temperature.

[0066] 2. Calculate the Reynolds number R of the flow field according to the range of fluid parameter changes in the pipeline e The span interval [R e min , R e max ] Flow field Reynolds number R e Calculate according to the following formula:

[0067]

[0068] In the formula, ρ is the fluid density; V is the average axial velocity in the pipe; d is the pipe diameter; μ is the fluid kinematic viscosity.

[0069] 3. R e The span interval [R e max , R e max ] is equally divided on the logarithmic coordinate axis with base 10 to obtain n Reynolds number nodes, n ≥ 7. Through different combinations of flow, temperature, and pressure, m flow field operating points are designed for each Reynolds number, m ≥ 3. The Reynolds number nodes and corresponding flow field conditions shown in Table 1 are obtained.

[0070] Table 1 Reynolds number nodes and corresponding flow field conditions

[0071] <![CDATA[R e min ]]> <![CDATA[R e 2 ]]> <![CDATA[R e 3 ]]> … <![CDATA[R e max ]]> Condition 1 <![CDATA[q v11 t 11 p 11 ]]> <![CDATA[q v21 t 21 p 21 ]]> <![CDATA[q v31 t 31 p 31 ]]> <![CDATA[q vn1 t n1 p n1 <!-- 4 -->]]> Condition 2 <![CDATA[q v12 t 12 p 12 ]]> <![CDATA[q v22 t 22 p 22 ]]> <![CDATA[q v32 t 32 p 32 ]]> <![CDATA[q vn2 t n2 p n2 ]]> … Working condition <![CDATA[q v1m t 1m p 1m ]]> <![CDATA[q v2m t 2m p 2m ]]> <![CDATA[q v3m t 3m p 3m ]]> <![CDATA[q vn m t nm p nm ]]>

[0072] 4. According to the parameters in step 1, build a system model measured by the ultrasonic flowmeter in the numerical simulation software. The modeling range is based on the ultrasonic flowmeter measurement point, at least 50D from the upstream pipeline and at least 20D from the downstream pipeline. If there are valves and other equipment within the above range, the valve can be simplified to a variable diameter, and the variable diameter aperture is calculated according to the valve size.

[0073] 5. Set the boundary conditions for numerical simulation calculation. The volume flow rate, fluid temperature, and fluid pressure under each working condition in Table 1 are used as the boundary conditions for numerical calculation; perform numerical calculations on each working point, and obtain flow field data after the calculation converges, including the position parameters, velocity parameters, pressure, temperature, kinematic viscosity, dynamic viscosity, density, etc. of each point.

[0074] 6. Use Gauss-Legendre numerical integration method to determine the channel position x of the multi-channel ultrasonic flowmeter i and weighted value w i The axial average velocity is calculated by the following formula.

[0075]

[0076] Where V measure is the average axial velocity, V i is the average speed of sound along the sound channel, x i is the channel position of the multi-channel ultrasonic flowmeter, w i It is the weighted value of the channel position of the multi-channel ultrasonic flowmeter.

[0077] 7. Export the coordinate parameters and velocity coordinate parameters of each sound channel line in the x and y coordinate axes.

[0078] like Figure 4 As shown, the position coordinates of a point R on the AB channel in the x, y coordinate system are (L Rx , L Ry ), the velocity coordinate is (V Rx , V Ry ). A single-axis coordinate system in the AB direction is established with A as the origin, and the position coordinates of point R are The velocity coordinate is

[0079] In summary, the position and velocity coordinates of R are The average sound velocity V along the sound channel line is calculated using the integral method of the following formula: AB .

[0080]

[0081] Where V ABis the average speed of sound along the sound channel.

[0082] 8. Repeat step 7 for the remaining channel parameters to calculate the average sound velocity V1, V2, V3, ... V of the multi-channel ultrasonic flowmeter on each channel line. a . And execute step 6 to obtain the axial average flow velocity V measured under each working condition measure , as shown in Table 2.

[0083] Table 2 Average axial flow velocity measured under various working conditions

[0084] <![CDATA[R e min ]]> <![CDATA[R e 2 ]]> <![CDATA[R e 3 ]]> … <![CDATA[R e max ]]> Condition 1 <![CDATA[V 11 measure ]]> <![CDATA[V 21 measure ]]> <![CDATA[V 31 measure ]]> <![CDATA[V 41 measure ]]> Condition 2 <![CDATA[V 12 measure ]]> <![CDATA[V 22 measure ]]> <![CDATA[V 32 measure ]]> <![CDATA[V 42 measure ]]> … Working condition <![CDATA[V 13 measure ]]> <![CDATA[V 23 measure ]]> <![CDATA[V 33 measure ]]> <![CDATA[V 43 measure ]]>

[0085] 9. Due to the calculation error of numerical simulation, the axial average flow velocity on the middle section of the transducer is used as the theoretical true value; the actual axial average flow velocity V of each working condition is obtained by double integration of the circular section. acutal , as shown in Table 3.

[0086]

[0087] Where V rθ is the axial velocity at each integration point, and R is the radius of the circular section.

[0088] Table 3 Actual average axial flow velocity under various working conditions

[0089] <![CDATA[R e min ]]> <![CDATA[R e 2 ]]> <![CDATA[R e 3 ]]> … <![CDATA[R e max ]]> Condition 1 <![CDATA[V 11 acutal ]]> <![CDATA[V 21 acutal ]]> <![CDATA[V 31 acutal ]]> <![CDATA[V 41 acutal ]]> Condition 2 <![CDATA[V 12 acutal ]]> <![CDATA[V 22 acutal ]]> <![CDATA[V 32 acutal ]]> <![CDATA[V 42 acutal ]]> … Working condition <![CDATA[V 13 acutal ]]> <![CDATA[V 23 acutal ]]> <![CDATA[V 33 acutal ]]> <![CDATA[V 43 acutal ]]>

[0090] 10. Calculate the deviation σ between the measured average axial flow velocity and the actual average axial flow velocity under each operating condition.

[0091]

[0092] Where σ is the measurement deviation; V measure is the average axial velocity; V acutal is the actual average axial velocity.

[0093] 11. The average of the measurement deviations σ under various Reynolds number conditions is obtained to obtain the average measurement deviation σ′, as shown in Table 4.

[0094] Table 4 Average axial velocity measurement deviation under various Reynolds number conditions

[0095] <![CDATA[R e min ]]> <![CDATA[R e 2 ]]> <![CDATA[R e 3 ]]> … <![CDATA[R e max ]]> Average measurement deviation <![CDATA[σ′1]]> <![CDATA[σ′2]]> <![CDATA[σ′3]]> <![CDATA[σ′ n ]]>

[0096] 12. Perform polynomial fitting on the average measurement deviation and Reynolds number in Table 4 to obtain the fitting formula σ=f(R e ). In the multi-channel ultrasonic flowmeter, the velocity profile correction is performed on the measured value, and the correction coefficient is:

[0097]

[0098] In the formula, K σ is the correction coefficient, and σ′ is the average measurement deviation.

[0099] 13. The average axial velocity measured by correction coefficient is:

[0100]

[0101] Where V is the corrected average axial velocity.

[0102] The present invention uses numerical simulation technology to simulate and calculate multiple characteristic working conditions in a specific application scenario of a multi-channel ultrasonic flowmeter, and obtains flow field data under each characteristic working condition. The specific application scenario refers to the flowmeter being installed in a fixed position, and the upstream and downstream pipeline layouts are clear. The characteristic working condition is based on the flow field Reynolds number R e As a key reference value, the Reynolds number is the main factor affecting the velocity profile of the flow field under the premise that the application scenario remains unchanged. The average axial velocity calculated by integration on the cross section at the middle position of the multi-channel flowmeter is taken as the actual average axial velocity V actual The velocity along the channel direction calculated by the linear integration method on each channel is the average sound velocity of the channel. The Gauss-Legendre numerical integration method can be used to obtain the average axial velocity V of the ultrasonic flowmeter. measure Calculate the measurement deviation σ of the ultrasonic flowmeter under each characteristic working condition and fit R e In the multi-channel ultrasonic flowmeter, the velocity profile correction factor K is introduced. σ , and then correct the flow measurement results.

[0103] In the prior art, when the flow field conditions (such as the Reynolds number) vary within a large range, the velocity profile of the fluid in the pipe will be deformed, or the pipe section upstream of the measurement position is poor, the straight pipe section is insufficient, and the velocity profile is asymmetrically arranged, which will affect the measurement accuracy. Therefore, the present invention introduces a velocity profile correction coefficient to eliminate the impact of the change on the measurement accuracy. After the velocity profile correction coefficient is introduced, the measurement error caused by the uneven flow field in the pipeline and the deformation of the velocity profile with the Reynolds number can be eliminated. If a multi-channel flow meter wants to pass a certain accuracy calibration measurement, it must be at the minimum flow rate q min To the maximum value of the flow rate on the label q max A certain accuracy can be guaranteed between min At least 0.3m / s. If the flow meter requires higher accuracy and flow range (q min ,q max) span is large, and the measurement error introduced by the velocity profile will cause the flow meter to fail the calibration. Using the method described in this patent to correct the flow calculation can improve the stability of the multi-channel flow meter's measurement accuracy during the calibration process.

[0104] The above numerical simulation calculation is performed on a multi-channel ultrasonic flowmeter with a pipe diameter of 250mm, a water temperature of 20℃, and a pressure of 0.3MPa. Under the working condition of a flow rate of 0.3m / s, the measurement deviation is 0.58%. When the flow rate reaches above 6m / s, the measurement deviation is about 0.05%. If the flowmeter requires a measurement accuracy of 0.3%, the influence of the simple velocity profile change on the measurement accuracy can no longer guarantee the measurement accuracy. By introducing the correction factor K σ , which can eliminate the measurement error caused by the velocity profile and improve the flow meter calibration accuracy.

[0105] The present invention proposes a velocity profile correction calculation method for compensating for the influence of velocity profile changes with Reynolds number on measurement accuracy, and ensuring that the ultrasonic flowmeter has stable measurement accuracy under a large range of Reynolds number changes in specific application scenarios (upstream and downstream pipe section layout, pipe section roughness, etc.). The present invention calculates the average velocity of the ultrasonic flowmeter along the sound channel direction by a linear integration method, uses this as the measurement velocity of the ultrasonic transducer, and uses numerical simulation data to obtain the measurement value of the ultrasonic flowmeter; Re is used as the key value to design the characteristic working condition boundary conditions of the numerical calculation, obtains the measurement deviation σ under each Reynolds number Re, and obtains the fitting relationship.

[0106] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with this technology to understand the contents of the present invention and implement them accordingly. They cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A flow calculation method suitable for a multi-channel ultrasonic flowmeter, characterized in that: The steps include: 1) According to the use requirements and equipment parameters of the multi-channel ultrasonic flowmeter, confirm the layout of the upstream and downstream pipe sections of the measurement location, confirm the pipe diameter and wall roughness between the ultrasonic transducers, and confirm the range of variation of the fluid parameters in the pipeline; 2) According to the variation range of fluid parameters in the pipeline, calculate the flow field Reynolds number R e The span interval; 3) R e The span interval is equally divided on the logarithmic coordinate axis to obtain n Reynolds number nodes, n ≥ 7, and m flow field operating points are designed for each Reynolds number through different flow, temperature, and pressure combinations, m ≥ 3; 4) Build a system model measured by the ultrasonic flowmeter in the numerical simulation software and set the boundary conditions for the numerical simulation calculation; 5) Based on the system model in step 4), numerical calculation is performed on each operating point, and flow field data is obtained after the calculation converges; 6) The Gauss-Legendre numerical integration method is used to determine the channel position and weighting value of the multi-channel ultrasonic flowmeter, and the axial average flow velocity is calculated; 7) deriving the coordinate parameters and velocity coordinate parameters of each sound channel line in the coordinate axis, and calculating the average sound velocity along the sound channel line; 8) Repeat step 7) for each other channel parameter to find the average sound velocity of the multi-channel ultrasonic flowmeter on each channel line; and repeat step 6) to obtain the measured axial average flow velocity V under each working condition. measure ; 9) The axial average flow velocity on the middle section of the transducer is taken as the theoretical true value, and the actual axial average flow velocity V of each working condition is obtained by the integration method. acutal ; 10) Calculate the deviation between the measured average axial flow velocity and the actual average axial flow velocity under each working condition; 11) averaging the measurement deviations under various Reynolds number conditions to obtain an average measurement deviation; 12) Perform polynomial fitting on the average measurement deviation and Reynolds number to obtain a fitting formula; perform velocity profile correction on the measured value in the multi-channel ultrasonic flowmeter, and the correction coefficient is: In the formula, K σ is the correction coefficient, σ' is the average measurement deviation; 13) Correct the measured average axial velocity according to the correction factor.

2. The calculation method according to claim 1, characterized in that: The fluid parameters in step 1) include flow rate, pressure, and temperature.

3. The calculation method according to claim 1, characterized in that: The Reynolds number R of the flow field in step 2) e Calculated by the following formula: Where ρ is the fluid density; V is the average axial velocity in the pipe; d is the pipe diameter; and μ is the kinematic viscosity of the fluid.

4. The calculation method according to claim 1, characterized in that: The modeling range of the system model in step 4) is based on the ultrasonic flow meter measurement point, with the upstream pipeline being at least 50D and the downstream pipeline being at least 20D.

5. The calculation method according to claim 1, characterized in that: The boundary conditions in step 4) use the volume flow rate, fluid temperature, and fluid pressure under the various operating conditions in step 3) as the boundary conditions for numerical calculation.

6. The calculation method according to claim 1, characterized in that: The axial average flow velocity in step 6) is calculated by the following formula: Where V measure is the average axial velocity, V i is the average speed of sound along the sound channel, x i is the channel position of the multi-channel ultrasonic flowmeter, w i It is the weighted value of the channel position of the multi-channel ultrasonic flowmeter.

7. The calculation method according to claim 4, characterized in that: The average sound velocity along the sound channel line in step 7) is calculated by the following steps: 1) Set the position coordinates of a point R on the AB channel in the x, y coordinate system to (L Rx , L Ry ), the velocity coordinate is (V Rx , V Ry ); 2) A(L Ax , L Ay ) is used as the origin to establish a single-axis coordinate system in the AB direction. The position coordinate of point R is the distance from point A to point A. The speed value is The position and velocity coordinates of R are 3) Calculate the average speed of sound along the sound channel line using the following formula: Where V AB is the average sound speed along the sound channel, L A is the position coordinate of point A, L B is the position coordinate of point B.

8. The calculation method according to claim 1, characterized in that: The measurement deviation σ in step 10) is calculated by the following formula: Where σ is the measurement deviation; V measure is the average axial velocity; V acutal is the actual average axial velocity.

9. The calculation method according to claim 8, characterized in that: The average axial velocity obtained by correcting the measurement with the correction factor is: Where V is the corrected average axial velocity.

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