Method for releasing retained air mass of long-distance pressure water conveying pipeline

Abstract

The invention discloses a long-distance pressure water conveying pipeline retention air mass discharging method which comprises the following steps: S1, in the water filling process of a long-distance pressure horizontal water conveying pipeline, detecting whether retention air mass exists in the pipeline or not through a flow-pressure difference correlation analysis method; s2, when the retained air mass exists in the horizontal water conveying pipeline, geometric parameters of the retained air mass in the horizontal pipeline are obtained based on an ultrasonic imaging inversion technology, and a dimensionless number n is calculated according to the geometric parameters; s3, when n is larger than 0.8, according to the critical Friedel number, the gravitational acceleration and the diameter of the water conveying pipeline, the starting flow speed of the retention air mass is calculated; s4, when n is smaller than or equal to 0.8, multiple stresses of the retained air mass in the horizontal water conveying pipeline are calculated according to the geometric parameters, and the starting flow speed of the retained air mass is calculated through the multiple stresses; and S5, a water conveying power mechanism of the water conveying pipeline is controlled to adjust the flow of the water conveying pipeline till the average flow speed of the water conveying pipeline is larger than the starting flow speed, and the retained air mass is conveyed to a downstream exhaust valve of the water conveying pipeline to be discharged.

Description

Technical Field

[0001] The present invention belongs to the technical field of safe water transmission in water network projects, and in particular relates to a method for releasing trapped air masses in a long-distance pressurized water transmission pipeline. Background Art

[0002] As global water shortages intensify, long-distance pressurized water pipelines have become core infrastructure for inter-basin water transfer and urban water supply, and a vital component of the national water grid. Due to the fluctuating terrain and geology of water lines, air pockets can easily form in localized locations during the filling process. This not only affects water delivery efficiency (increasing energy consumption) but also poses safety risks to project operations (transient flow can lead to gas explosions and burst pipes). Currently, installing air vents on long-distance water pipelines is a key measure to address this problem.

[0003] In long-distance pressurized water pipeline systems, to achieve the release of trapped air masses, two key issues need to be addressed: first, how to use water flow to drive the trapped air masses along the pipeline, and second, to coordinate the movement of the air masses by installing exhaust valves at appropriate downstream locations. When driving the trapped air masses along the pipeline, if the water flow rate is too low, the air masses will be difficult to be driven by the water flow, causing them to remain in the pipeline; if the water flow rate is too high, it may cause pressure fluctuations in the pipeline and even produce water hammer, causing gas explosions and damaging the pipeline. Therefore, it is necessary to determine the starting flow rate of the trapped air mass in order to accurately control the water flow and ensure that the water flow can drive the air mass at an appropriate flow rate, causing it to move downstream along the pipeline.

[0004] At present, in the study of the starting velocity of trapped air masses, scholars have focused on the critical starting velocity of large air pockets and used the dimensionless number n of the bubble volume relative to the diameter of the water pipe as the basis for classifying air pocket types. The calculation formula for n is: n is the dimensionless number of bubble volume relative to the pipe diameter; V a is the volume of the bubble, m 3 ; D is the diameter of the pressurized water pipeline, m.

[0005] When n>0.8, the critical velocity of the trapped air mass is proportional to the acceleration of gravity and the square root of the pipe diameter (which can be measured by the critical Fred number, which is about 0.35-0.55 for horizontal pipes). At this time, the volume of the air mass does not need to be considered, and it can be calculated according to the formula Calculate the starting velocity v of the trapped air mass w .

[0006] However, in actual large-scale water supply projects, small stagnant air masses often appear in the pipelines, that is, the dimensionless number n is less than 0.8. At this scale, tiny forces such as surface tension cannot be ignored, and dynamic analysis is required. Currently, there is no method to determine the starting flow rate of such stagnant air masses. Summary of the Invention

[0007] In view of the above-mentioned deficiencies in the prior art, the present invention provides a method for releasing trapped air masses in long-distance pressurized water pipelines, which can accurately determine the starting flow rate for discharging trapped air masses of different sizes.

[0008] In order to achieve the above-mentioned object of the invention, the technical solution adopted by the present invention is:

[0009] A method for releasing trapped air masses in a long-distance pressurized water pipeline is provided, comprising the following steps:

[0010] S1. During the filling process of a long-distance pressurized horizontal water pipeline, the flow-pressure differential correlation analysis method is used to detect whether there is trapped air in the pipeline;

[0011] S2. When there is a trapped air mass in the horizontal water pipeline, the geometric parameters of the trapped air mass in the horizontal pipeline are obtained based on ultrasonic imaging inversion technology, and the dimensionless number n is calculated based on the geometric parameters;

[0012] S3. When n>0.8, calculate the starting velocity of the trapped air mass based on the critical Fried number, gravitational acceleration and the diameter of the water pipe;

[0013] S4. When n≤0.8, multiple forces acting on the trapped air mass in the horizontal water pipe are calculated based on the geometric parameters, and the starting flow velocity of the trapped air mass is calculated using the multiple forces.

[0014] S5. Control the water transmission power mechanism of the water transmission pipeline to adjust the flow of the water transmission pipeline until the average flow velocity of the water transmission pipeline is greater than the starting flow velocity, so as to transport the retained air mass to the exhaust valve downstream of the water transmission pipeline for discharge.

[0015] Furthermore, step S4 further includes:

[0016] S41. When n≤0.8, calculate the projected area A of the trapped air mass perpendicular to the fluid flow direction based on the geometric parameters. d and the projected area A parallel to the fluid flow direction s ;

[0017] S42, according to the projection area A d and the projected area A s , calculate the buoyancy of the trapped air mass F B , gravity of the trapped air mass F Gand the components of the surface tension force F in the x and y directions Sx and F Sy ;

[0018] S43, according to the buoyancy of the trapped air mass F B , gravity of the trapped air mass F G and component F Sx and F Sy , calculate the starting velocity of the trapped air mass:

[0019]

[0020] Among them, v w is the starting flow rate; μ is the dynamic viscosity of the liquid; C D is the drag coefficient; ρ l is the density of the liquid phase; C l is the shear lift coefficient.

[0021] The beneficial effects of the above technical solution are:

[0022] (1) Accurately determine the starting flow rate: This invention uses different calculation methods to determine the starting flow rate for different sizes of trapped air masses by distinguishing the size of the dimensionless number n. When n>0.8, the calculation is based on parameters such as the critical Fried number; when n≤0.8, the calculation is determined by calculating multiple forces acting on the air mass. This method greatly improves the accuracy of the starting flow rate determination and provides a key guarantee for the subsequent release of the air mass.

[0023] (2) Effectively realize the release of air masses: After determining the starting flow rate, the flow rate of the water pipeline can be adjusted by controlling the water transmission power mechanism of the water pipeline so that the average flow rate is greater than the starting flow rate, thereby smoothly transporting the retained air masses to the downstream exhaust valve for release, effectively solving the problem of retained air masses in long-distance pressurized water pipelines, and avoiding the adverse effects of air masses on the water transmission system such as obstructing water flow, affecting water transmission efficiency, and causing pipeline vibration.

[0024] (3) Adopting a variety of advanced technologies: Comprehensively using the flow-pressure difference correlation analysis method to detect air masses and ultrasonic imaging inversion technology to obtain air mass geometric parameters. The combination of these technologies makes the monitoring of trapped air masses and parameter acquisition more efficient and accurate, and enhances the reliability and practicality of the entire release method.

[0025] Furthermore, the buoyancy of the trapped air mass F is calculated B , gravity of the trapped air mass F G and component F Sx and F Sy The expression is:

[0026] F B =ρ l gV a、F G =ρ a gV a

[0027]

[0028] Where g is the acceleration due to gravity; ρ a is the density of the gas phase; V a is the volume of the stagnant air mass; a is the maximum length of the stagnant air mass; α and β are the forward and backward tilt angles of the stagnant air mass, respectively.

[0029] Furthermore, the drag coefficient is calculated using the Tomiyama model. During the calculation process, the drag coefficient is calculated for any given starting flow velocity, and then iterative updates are performed until the starting flow velocity converges to obtain the drag coefficient. The Tomiyama model is:

[0030]

[0031] Among them, ρ a is the density of the gas phase; μ is the dynamic viscosity of the liquid; d b is the characteristic length of the trapped air mass; is the acceleration of gravity; σ is the surface tension coefficient of the gas-liquid interface; Re b and Eo are the Reynolds number and Bond number of the trapped air mass, respectively.

[0032] Furthermore, when n>0.8, the expression for calculating the starting flow velocity of the trapped air mass is:

[0033]

[0034] Among them, v w is the starting flow velocity; k is the critical Fried number; g is the acceleration of gravity; and D is the diameter of the water pipe.

[0035] Furthermore, step S1 further includes:

[0036] S11. Use pressure sensors to collect pressure data of long-distance pressurized horizontal water pipelines within a preset time period and calculate the average pressure

[0037]

[0038] Where n is the total number of pressure data collected within the preset time; p i is the i-th pressure data;

[0039] S12. Calculate the standard deviation of pressure fluctuations based on the pressure data and average pressure within a preset time period:

[0040]

[0041] Among them, σ p is the standard deviation of pressure fluctuation;

[0042] S13. Calculate the pipeline pressure difference fluctuation coefficient based on the standard deviation of pressure fluctuation and the average pressure:

[0043]

[0044] Among them, C p is the pipeline pressure difference fluctuation coefficient;

[0045] S14. Draw a flow rate and pressure difference curve Q-ΔP based on the flow rate of a long-distance pressurized horizontal water pipeline;

[0046] S15, when the pipeline pressure difference fluctuation coefficient C p When the value is greater than a preset threshold or the curve Q-ΔP deviates from the preset linear ratio, it indicates that there is a trapped air mass in the pipeline.

[0047] The beneficial effects of the above technical solution are:

[0048] (1) In terms of trapped air mass detection, the system collects data through pressure sensors, calculates the average pressure, the standard deviation of pressure fluctuations, and the pipeline pressure differential fluctuation coefficient, and combines the flow rate and pressure differential curves to accurately and efficiently detect the presence of trapped air masses in the pipeline. This detection method is based on actual operating data, is real-time and reliable, and can promptly identify potential problems and avoid water delivery failures caused by air mass accumulation.

[0049] (2) In parameter calculation and flow rate determination, different formulas are used for different situations. For example, specific formulas are used to calculate the buoyancy, gravity, and surface tension components of the trapped air mass to provide accurate data for subsequent calculations. The Tomiyama model is used to iteratively calculate the drag coefficient to improve calculation accuracy. Different formulas are used to calculate the starting flow rate based on the size of the dimensionless number n. This refined calculation method greatly improves the accuracy of determining the starting flow rate. Accurate starting flow rate calculation is the key to effectively expelling trapped air masses, which helps to improve water transmission efficiency, reduce air mass damage to the pipeline system, and ensure the stable and safe operation of long-distance pressurized water pipelines.

[0050] Furthermore, the method for obtaining the geometric parameters of the trapped air mass in the horizontal pipeline based on ultrasonic imaging inversion technology includes:

[0051] S21. Moving an annular or linear array ultrasonic probe uniformly arranged along the circumference of a long-distance pressurized water pipeline, and synchronously emitting multi-frequency pulsed sound waves, to collect full-section reflected wave, scattered wave, and transmitted wave signals in real time;

[0052] S22. Based on the real-time collection of full-section reflected wave, scattered wave, and transmitted wave signals, a full waveform inversion algorithm is used to map the acoustic wave propagation time difference and energy attenuation into the sound velocity and acoustic impedance distribution of the pipeline cross section;

[0053] S23. Based on the sound velocity and acoustic impedance distribution of the pipeline cross section, a finite element model is used to construct a three-dimensional image of the long-distance pressurized water pipeline. The guided wave modes are separated by a matching pursuit algorithm to identify the air mass boundaries.

[0054] S24. Use ultrasonic CT technology to generate a color cloud map of the trapped air mass and obtain the geometric parameters of the trapped air mass: maximum length a, maximum width b, maximum thickness c, air mass forward tilt angle α, backward tilt angle β, and the projected area A of the trapped air mass in the direction parallel to the fluid flow and in the direction perpendicular to the fluid flow. s 、A d .

[0055] The beneficial effects of the above technical solution are:

[0056] (1) Comprehensive detection: Ultrasonic probes are evenly arranged along the circumference of the pipeline and simultaneously emit multi-frequency pulse sound waves, which can comprehensively collect reflected wave, scattered wave, and transmitted wave signals from the entire cross-section of the pipeline. This ensures the integrity of the acquired information, avoids the omission of key data, and provides sufficient basis for accurately judging the status of the air mass.

[0057] (2) Data processing accuracy: The full waveform inversion algorithm accurately maps the acoustic wave propagation time difference and energy attenuation into the sound velocity and acoustic impedance distribution of the pipeline cross section. This process lays a solid foundation for the subsequent construction of three-dimensional stereo images, making the analysis of the internal conditions of the pipeline more scientific and accurate.

[0058] (3) Image construction and recognition accuracy: The finite element model combined with the matching pursuit algorithm can not only construct a three-dimensional image of a long-distance pressurized water pipeline, but also accurately separate the guided wave modes and identify the air mass boundaries. This makes the morphological information of the air mass more intuitive and clear, helping to gain a deeper understanding of the shape and location of the air mass.

[0059] (4) Parameter acquisition effectiveness: The color cloud image generated by ultrasonic CT technology can directly obtain multiple geometric parameters of the trapped air mass, such as maximum length, width, thickness, inclination, and projected area. These precise geometric parameters provide key data support for the subsequent accurate calculation of the air mass force and starting flow rate, improving the accuracy and effectiveness of the trapped air mass release method and ensuring the stable operation of the water pipeline system.

[0060] Furthermore, the layout principle of the exhaust valve is:

[0061] When the water supply pipeline is a combination of horizontal and down-slope pipelines, an exhaust valve is set at the end of the horizontal pipeline; when the water supply pipeline is a combination of horizontal and up-slope pipelines, an exhaust valve is set at the end of the up-slope pipeline.

[0062] Furthermore, the long-distance pressurized horizontal water pipeline is arranged in a long-distance pressurized water tunnel.

[0063] The beneficial effects of the present invention are as follows: when the dimensionless number n≤0.8, the force exerted on the trapped air mass in the water flow can be determined by the geometric parameters of the trapped air mass, and the starting speed of the smaller trapped air mass can be calculated to accurately provide the water flow rate, thereby ensuring the discharge of the trapped air mass in the water pipeline, thereby avoiding the drastic change in local flow velocity caused by the trapped air mass compressing the flow channel and inducing pressure pulses, thereby improving the water delivery efficiency and pipeline safety of long-distance water pipelines. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] Figure 1 This is a flow chart of the method for releasing trapped air masses in long-distance pressurized water pipelines.

[0065] Figure 2 This is a force analysis diagram of trapped air masses in long-distance pressurized horizontal water pipelines.

[0066] Figure 3 Flowchart for calculating the starting velocity of the trapped air mass when n≤0.8. DETAILED DESCRIPTION

[0067] The specific embodiments of the present invention are described below to facilitate understanding of the present invention by those skilled in the art. However, it should be clear that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the appended claims, these changes are obvious, and all inventions and creations utilizing the concepts of the present invention are protected.

[0068] refer to Figure 1 , Figure 1 The flow chart of the method for releasing trapped air masses in long-distance pressurized water pipelines is shown; Figure 1 As shown, the method S includes steps S1 to S5.

[0069] In step S1, during the water filling process of the long-distance pressurized horizontal water pipeline, the flow-pressure difference correlation analysis method is used to detect whether there is a trapped air mass in the pipeline; if not, step S1 is continued.

[0070] In one embodiment of the present invention, step S1 further includes:

[0071] S11. Use pressure sensors to collect pressure data of long-distance pressurized horizontal water pipelines within a preset time period and calculate the average pressure

[0072]

[0073] Where n is the total number of pressure data collected within the preset time; p i is the i-th pressure data;

[0074] High-precision pressure sensors (spacing ≤ 2km) are arranged along long-distance pressurized horizontal water pipelines, and ultrasonic flow meters are arranged at the beginning and end of the pipelines to collect flow (Q) and pressure difference (ΔP) data in real time.

[0075] S12. Calculate the standard deviation of pressure fluctuations based on the pressure data and average pressure within a preset time period:

[0076]

[0077] Among them, σ p is the standard deviation of pressure fluctuation;

[0078] S13. Calculate the pipeline pressure difference fluctuation coefficient based on the standard deviation and average pressure of the pressure fluctuation:

[0079]

[0080] Among them, C p is the pipeline pressure difference fluctuation coefficient;

[0081] S14. Draw a flow rate and pressure difference curve Q-ΔP based on the flow rate of a long-distance pressurized horizontal water pipeline;

[0082] S15, when the pipeline pressure difference fluctuation coefficient C p When the value is greater than a preset threshold or the curve Q-ΔP deviates from the preset linear ratio, it indicates that there is a trapped air mass in the pipeline.

[0083] Under stable flow conditions, the pipeline pressure difference fluctuation coefficient C p Usually it is in the range of 0.05 to 0.10 (i.e. the standard deviation is 5% to 10% of the average pressure difference). At this time, the flow rate Q and the pressure difference ΔP strictly follow The linear relationship (R 2 ≥0.98).

[0084] When there is a trapped air mass in the pipeline, C p It will rise significantly to above 0.15, or even exceed 0.30, or the Q-ΔP curve will deviate from linearity by more than 10%. This is because the air mass compresses the flow channel, causing a sharp change in local flow velocity and triggering pressure pulses.

[0085] In step S2, when there is a trapped air mass in the horizontal water pipeline, the geometric parameters of the trapped air mass in the horizontal pipeline are obtained based on the ultrasonic imaging inversion technology, and the dimensionless number n is calculated based on the geometric parameters;

[0086] In one embodiment of the present invention, a method for obtaining geometric parameters of trapped air masses in a horizontal pipeline based on ultrasonic imaging inversion technology includes:

[0087] S21. Move the annular or linear array ultrasonic probes that are evenly arranged circumferentially along the long-distance pressurized water pipeline, and synchronously emit multi-frequency pulse sound waves to collect full-section reflected wave, scattered wave and transmitted wave signals in real time; this solution preferably uses a mechanical crawling device to drive the movement of the evenly arranged annular or linear array ultrasonic probes.

[0088] S22. Based on the real-time collection of full-section reflection, scattered, and transmitted wave signals, a full waveform inversion algorithm (such as ART / SIRT) is used to map the acoustic wave propagation time difference and energy attenuation into the sound velocity and acoustic impedance distribution of the pipeline cross section;

[0089] S23. Based on the sound velocity and acoustic impedance distribution of the pipeline cross section, a finite element model is used to construct a three-dimensional image of the long-distance pressurized water pipeline. The guided wave modes are separated by a matching pursuit algorithm to identify the air mass boundaries.

[0090] S24. Use ultrasonic CT technology to generate a color cloud map of the trapped air mass and obtain the geometric parameters of the trapped air mass: maximum length a, maximum width b, maximum thickness c, air mass forward tilt angle α, backward tilt angle β, and the projected area A of the trapped air mass in the direction parallel to the fluid flow and in the direction perpendicular to the fluid flow. s 、A d .

[0091] In step S3, when n>0.8, the starting flow rate of the trapped air mass is calculated based on the critical Fried number, gravitational acceleration, and the diameter of the water pipe:

[0092]

[0093] Among them, v w is the starting flow velocity, m / s; k is the critical Friedel number, 0.35≤k≤0.55; g is the acceleration of gravity, which is 9.8m / s 2 ; D is the diameter of the water pipe, m.

[0094] In step S4, when n≤0.8, multiple forces acting on the retained air mass in the horizontal water pipe are calculated based on the geometric parameters, and the starting flow velocity of the retained air mass is calculated using the multiple forces.

[0095] like Figure 3 As shown, during implementation, the preferred step S4 of this solution further includes:

[0096] S41. When n≤0.8, calculate the projected area A of the trapped air mass perpendicular to the fluid flow direction based on the geometric parameters. d and the projected area A parallel to the fluid flow direction s ;

[0097] S42, according to the projection area A d and the projected area A s , calculate the buoyancy of the trapped air mass F B , gravity of the trapped air mass F G and the components of the surface tension force F in the x and y directions Sx and F Sy The force analysis of trapped air masses in water pipelines can refer to Figure 2 .

[0098] S43, according to the buoyancy of the trapped air mass F B , gravity of the trapped air mass F G and component F Sx and F Sy , calculate the starting velocity of the trapped air mass:

[0099]

[0100] Among them, v w is the starting flow rate; μ is the dynamic viscosity of the liquid, which is 1.0016×10 -3 pa.s;C D is the drag coefficient; ρ l is the density of the liquid phase, the density of water is 1000 kg / m 3 ; C l is the shear lift coefficient.

[0101] Buoyancy of trapped air mass F B , gravity of the trapped air mass F G and component F Sx and F Sy The unit is N, the projected area A d and the projected area A s The unit is m 2 .

[0102] In this solution, the drag coefficient is preferably calculated using the Tomiyama model. During the calculation process, the drag coefficient is calculated for any given starting flow velocity, and then it is iterated and updated until the starting flow velocity converges to obtain the drag coefficient. The Tomiyama model is:

[0103]

[0104] Among them, ρ aThe density of the gas phase is 1.205 kg / m 3 ; μ is the dynamic viscosity of the liquid; d b is the characteristic length of the trapped air mass; is the acceleration due to gravity; σ is the surface tension coefficient of the gas-liquid interface, which is 0.072 N / m; Re b and Eo are the Reynolds number and Bond number of the trapped air mass, respectively.

[0105] In step S5, the water delivery power mechanism of the water delivery pipeline is controlled to adjust the flow of the water delivery pipeline until the average flow rate of the water delivery pipeline is greater than the starting flow rate, so as to transport the retained air mass to the exhaust valve downstream of the water delivery pipeline for discharge.

[0106] In step S4, the buoyancy of the trapped air mass F is calculated B , gravity of the trapped air mass F G and component F Sx and F Sy The expression is:

[0107] F B =ρ l gV a 、F G =ρ a gV a

[0108]

[0109] Where g is the acceleration due to gravity; ρ a is the density of the gas phase; V a is the volume of the stagnant air mass; a is the maximum length of the stagnant air mass; α and β are the forward and backward tilt angles of the stagnant air mass, respectively.

[0110] In implementation, this solution preferably follows the following principles for vent valve placement: When the water pipeline is a combination of horizontal and down-slope, install the vent valve at the end of the horizontal pipeline; when the water pipeline is a combination of horizontal and down-slope, install the vent valve at the end of the down-slope pipeline. Long-distance pressurized horizontal water pipelines are placed in long-distance pressurized water tunnels.

[0111] In summary, the method for releasing trapped air masses in long-distance pressurized water pipelines provided by this solution can accurately determine the starting speed for driving the movement of trapped air masses in the water pipeline, thereby ensuring the water transmission efficiency of the water pipeline.

Claims

1. A method for releasing trapped air masses in a long-distance pressurized water pipeline, characterized in that: Including steps: S1. During the filling process of a long-distance pressurized horizontal water pipeline, the flow-pressure differential correlation analysis method is used to detect whether there is trapped air in the pipeline; S2. When there is a trapped air mass in the horizontal water pipeline, the geometric parameters of the trapped air mass in the horizontal pipeline are obtained based on ultrasonic imaging inversion technology, and the dimensionless number n is calculated based on the geometric parameters; S3. When n>0.8, calculate the starting velocity of the trapped air mass based on the critical Fried number, gravitational acceleration and the diameter of the water pipe; S4. When n≤0.8, multiple forces acting on the trapped air mass in the horizontal water pipe are calculated based on the geometric parameters, and the starting flow velocity of the trapped air mass is calculated using the multiple forces. S5. Control the water transmission power mechanism of the water transmission pipeline to adjust the flow of the water transmission pipeline until the average flow velocity of the water transmission pipeline is greater than the starting flow velocity, so as to transport the retained air mass to the exhaust valve downstream of the water transmission pipeline for discharge.

2. The method for releasing trapped air masses in a long-distance pressurized water pipeline according to claim 1, characterized in that: Step S4 further comprises: S41. When n≤0.8, calculate the projected area A of the trapped air mass perpendicular to the fluid flow direction based on the geometric parameters. d and the projected area A parallel to the fluid flow direction s ; S42, according to the projection area A d and the projected area A s , calculate the buoyancy of the trapped air mass F B , gravity of the trapped air mass F G and the components of the surface tension force F in the x and y directions Sx and F Sy ; S43, according to the buoyancy of the trapped air mass F B , gravity of the trapped air mass F G and component F Sx and F Sy , calculate the starting velocity of the trapped air mass: Among them, v w is the starting flow rate; μ is the dynamic viscosity of the liquid; C D is the drag coefficient; ρ l is the density of the liquid phase; C l is the shear lift coefficient.

3. The method for releasing trapped air masses in a long-distance pressurized water pipeline according to claim 2, characterized in that: Calculate the buoyancy of the trapped air mass F B , gravity of the trapped air mass F G and component F Sx and F Sy The expression is: F B =ρ l gV a 、F G =ρ a gV a Where g is the acceleration due to gravity; ρ is the acceleration due to gravity. a is the density of the gas phase; V a is the volume of the stagnant air mass; a is the maximum length of the stagnant air mass; α and β are the forward and backward tilt angles of the stagnant air mass, respectively.

4. The method for releasing trapped air masses in a long-distance pressurized water pipeline according to claim 2, characterized in that: The drag coefficient is calculated using the Tomiyama model. During the calculation process, the drag coefficient is calculated for any given starting flow velocity, and then it is iterated and updated until the starting flow velocity converges to obtain the drag coefficient. The Tomiyama model is: Among them, ρ a is the density of the gas phase; μ is the dynamic viscosity of the liquid; d b is the characteristic length of the trapped air mass; is the acceleration of gravity; σ is the surface tension coefficient of the gas-liquid interface; Re b and Eo are the Reynolds number and Bond number of the trapped air mass, respectively.

5. The method for releasing trapped air masses in a long-distance pressurized water pipeline according to claim 1, characterized in that: When n>0.8, the expression for calculating the starting velocity of the trapped air mass is: Among them, v w is the starting flow velocity; k is the critical Fried number; g is the acceleration of gravity; D is the diameter of the water pipe.

6. The method for releasing trapped air masses in a long-distance pressurized water pipeline according to claim 1, characterized in that: Step S1 further comprises: S11. Use pressure sensors to collect pressure data of long-distance pressurized horizontal water pipelines within a preset time period and calculate the average pressure Where n is the total number of pressure data collected within the preset time; p i is the i-th pressure data; S12. Calculate the standard deviation of pressure fluctuations based on the pressure data and average pressure within a preset time period: Among them, σ p is the standard deviation of pressure fluctuation; S13. Calculate the pipeline pressure difference fluctuation coefficient based on the standard deviation and average pressure of the pressure fluctuation: Among them, C p is the pipeline pressure difference fluctuation coefficient; S14. Draw a flow rate and pressure difference curve Q-ΔP based on the flow rate of a long-distance pressurized horizontal water pipeline; S15, when the pipeline pressure difference fluctuation coefficient C p When the value is greater than a preset threshold or the curve Q-ΔP deviates from the preset linear ratio, it indicates that there is a trapped air mass in the pipeline.

7. The method for releasing trapped air masses in a long-distance pressurized water pipeline according to claim 1, characterized in that: The method for obtaining the geometric parameters of trapped air masses in horizontal pipelines based on ultrasonic imaging inversion technology includes: S21. Moving an annular or linear array ultrasonic probe uniformly arranged along the circumference of a long-distance pressurized water pipeline, and synchronously emitting multi-frequency pulsed sound waves, to collect full-section reflected wave, scattered wave, and transmitted wave signals in real time; S22. Based on the real-time collection of full-section reflected wave, scattered wave, and transmitted wave signals, a full waveform inversion algorithm is used to map the acoustic wave propagation time difference and energy attenuation into the sound velocity and acoustic impedance distribution of the pipeline cross section; S23. Based on the sound velocity and acoustic impedance distribution of the pipeline cross section, a finite element model is used to construct a three-dimensional image of the long-distance pressurized water pipeline. The guided wave modes are separated by a matching pursuit algorithm to identify the air mass boundaries. S24. Use ultrasonic CT technology to generate a color cloud map of the trapped air mass and obtain the geometric parameters of the trapped air mass: maximum length a, maximum width b, maximum thickness c, air mass forward tilt angle α, backward tilt angle β, and the projected area A of the trapped air mass in the direction parallel to the fluid flow and in the direction perpendicular to the fluid flow. s 、A d .

8. The method for releasing trapped air masses in a long-distance pressurized water pipeline according to claim 1, characterized in that: The layout principle of the exhaust valve is: When the water supply pipeline is a combination of horizontal and down-slope pipelines, an exhaust valve is set at the end of the horizontal pipeline; when the water supply pipeline is a combination of horizontal and up-slope pipelines, an exhaust valve is set at the end of the up-slope pipeline.

9. The method for releasing trapped air masses in a long-distance pressurized water pipeline according to any one of claims 1 to 8, characterized in that: The long-distance pressurized horizontal water pipeline is arranged in a long-distance pressurized water tunnel.

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