A FLUENT-based flow field analysis and optimization model for rainwater inspection wells and its application

Abstract

The application discloses a rainwater inspection well flow field analysis optimization model based on FLUENT and application thereof. The model establishes a rainwater inspection well flow model, extracts an inner flow channel structure, carries out grid division on the inner flow channel and detects grid quality, then imports the divided grid into FLUENT software, loads a turbulent flow energy model and a flow state model, sets a boundary condition, defines water and gas distribution in the inspection well and a pipeline system, carries out initialization setting, sets a solution step and iteration accuracy, carries out solution calculation, finally sets parameters and flow field characteristic cloud map monitoring, and checks flow field distribution. The rainwater inspection well flow field analysis method based on FLUENT can realize overall simulation analysis of the rainwater inspection well and the pipeline system, accurately reflects internal flow field change conditions, and the rainwater inspection well prepared according to the above model can effectively improve the flow capacity of the inspection well, reduce the risk of water flow blockage and overflow, and reduce water head loss caused by adverse flow state.

Description

Technical Field

[0001] This invention relates to a flow field model for rainwater inspection wells, specifically to a flow field analysis and optimization model for rainwater inspection wells based on FLUENT and its application, belonging to the field of inspection well technology. Background Technology

[0002] With the continuous development of urbanization and the increase in extreme weather events, existing drainage systems are unable to meet the drainage needs under high-intensity rainfall, leading to frequent urban flooding and seriously affecting people's quality of life. As an important component of the stormwater drainage system, the energy loss inherent in stormwater inspection wells is one of the significant reasons for the decline in the drainage capacity of the pipe network.

[0003] Current flow field analyses of stormwater drainage systems mostly focus on pipes and special structures. These analyses neglect energy loss within manholes and the interaction between manholes and pipes, resulting in significant errors compared to actual conditions. Accurate simulation of the flow field inside stormwater manholes allows for the analysis of their defects and deficiencies during the flow process, facilitating structural optimization and improvement. Summary of the Invention

[0004] To address the problems existing in the prior art, the first objective of this invention is to provide a flow field analysis and optimization model for rainwater inspection wells based on FLUENT. This model, based on the FLUENT flow field analysis method for rainwater inspection wells, can achieve overall simulation analysis of rainwater inspection wells and pipeline systems, more accurately reflecting the changes in their internal flow field, which is of great significance for the design and optimization of inspection wells.

[0005] The second objective of this invention is to provide an application of a FLUENT-based flow field analysis and optimization model for rainwater inspection wells, used to prepare high-drainage, low-resistivity rainwater inspection wells. Based on the realism and accuracy of the model's description of the internal flow field of the inspection well, the optimized high-drainage, low-resistivity rainwater inspection well can effectively improve the flow capacity of the rainwater inspection well, reduce the risk of water flow blockage and overflow, and reduce head loss caused by unfavorable flow conditions.

[0006] To achieve the above technical objectives, this invention provides a FLUENT-based optimization model for the flow field analysis of rainwater inspection wells, comprising:

[0007] Step S1: Establish a flow model of the rainwater inspection well and extract its internal flow channel structure;

[0008] Step S2: Use unstructured tetrahedral meshes to divide the internal flow channel structure and check the quality of the mesh after division;

[0009] Step S3: Import the divided mesh into FLUENT software and load the turbulent energy model and flow regime model;

[0010] Step S4: Set the boundary conditions of the model described in step S3. Based on the actual water filling conditions of the rainwater inspection well and pipeline system, define the water vapor distribution in the inspection well and pipeline system, and then perform initialization settings, setting the time iteration step, iteration accuracy and total iteration step, and then perform the solution calculation.

[0011] Step S5: Based on the calculation results obtained in step S4, set parameters and monitor the flow field characteristic cloud map to check the flow field distribution.

[0012] As a preferred option, the rainwater inspection well flow model is established using SOLIDWORK in ANSYS.

[0013] As a preferred embodiment, the internal flow channel structure is extracted using the Fill module in SOLIDWORK.

[0014] As a preferred option, when dividing the internal flow channel structure into grids, it is also necessary to select the grid size and reduce the number of grids.

[0015] As a preferred option, the quality of the divided mesh is tested using FLUENT software.

[0016] As a preferred embodiment, the turbulent energy model and the flow regime model are respectively selected as the VOF two-phase flow model and the RNG k-ε model, and the fluid properties are set as liquid water for the liquid phase and air for the gas phase.

[0017] As a preferred embodiment, the boundary condition setting process of the model is as follows: the upstream pipe inlet face is the velocity inlet, and the ratio of water phase to gas phase is set to 0~1; the manhole cover opening face is the velocity inlet, and the ratio of water phase to gas phase is set to 0~1; the downstream pipe outlet face is free outflow.

[0018] As a preferred embodiment, the initialization process is as follows: the region register is used to divide the liquid-gas phase distribution area at the initial flow time; the initialization of the overall model is performed using Initialization; and the Phase value is used in the Patch function to define that the upper space of the inspection well is filled with air at a pressure of standard atmospheric pressure, and the lower space is filled with water.

[0019] As a preferred embodiment, the time iteration step size is 0.001~0.005s, and the convergence residual is <10. -5 The total number of iterations is >20,000.

[0020] As a preferred embodiment, the process of monitoring the flow field characteristic cloud map is as follows: after importing the model calculation results into Tecplot, the velocity cloud map, velocity vector map, and streamline map of the motion at a specific cross section are extracted.

[0021] The present invention also includes an application of a flow field analysis and optimization model for rainwater inspection wells based on FLUENT, used to prepare high-drainage and low-resistivity rainwater inspection wells; the rainwater inspection well includes inspection well chambers and pipes that are orthogonally distributed, and a vent pipe is provided between the inspection well chambers and the pipes; the vent pipe is composed of a horizontal pipe (4), a vertical pipe (5) and a 90° elbow (6), wherein the horizontal pipe (4) is connected to the inspection well chamber (3) and the vertical pipe (5) is connected to the downstream pipe section (2) of the inspection well.

[0022] After the manhole provided by this invention is equipped with a vent pipe, the turbulence in the downstream pipeline is weakened, the flow velocity classification is significantly improved, and the water flow gradually returns to stability as it flows along the pipeline. This indicates that adding a vent pipe can effectively improve the flow pattern in the downstream pipeline of the manhole and reduce the energy loss caused by the turbulence.

[0023] As a preferred embodiment, the diameter of the ventilation pipe is 0.08~0.15m.

[0024] The vertical distance 'a' between the horizontal pipe and the downstream pipe section of the inspection well is determined by Equation 1:

[0025] Equation 1: a = xD;

[0026] In Equation 1, x ranges from 1 to 2 and is dimensionless; D is the diameter of the downstream pipe section of the inspection well, and its dimension is m.

[0027] As a preferred embodiment, the horizontal distance b between the vertical pipe and the inspection well chamber is determined by Equation 2:

[0028] Formula 2: b =yD;

[0029] In Equation 2, the value of y ranges from 5 to 10 and is dimensionless; D is the diameter of the downstream pipe section of the inspection well, with the dimension in meters.

[0030] Compared with the prior art, the beneficial technical effects of the technical solution of the present invention are as follows:

[0031] 1) The model provided by this invention is based on the FLUENT stormwater manhole flow field analysis method, which can realize the overall simulation analysis of stormwater manholes and pipeline systems, and more accurately reflect the changes in their internal flow field, which is of great significance for the design and optimization of manholes.

[0032] 2) In the technical solution provided by the present invention, based on the authenticity and accuracy of the description of the internal flow field of the inspection well by the above model, the optimized high-drainage and low-resistivity rainwater inspection well can effectively improve the flow capacity of the rainwater inspection well, reduce the risk of water flow blockage and overflow, and reduce the head loss caused by unfavorable flow conditions. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of a common rainwater inspection well structure in existing technology;

[0034] Among them, 1-upstream pipe section of inspection well, 2-downstream pipe section of inspection well, 3-manhole of inspection well;

[0035] Figure 2 This is a schematic diagram of the flow field in a common rainwater inspection well in the prior art;

[0036] in, Figure 2 (a) is the velocity contour plot of the cross-sectional motion. Figure 2 (b) is the velocity vector diagram of the cross-sectional motion. Figure 2 (c) is a streamline diagram of the cross-sectional motion;

[0037] Figure 3 This is a schematic diagram of the optimized inspection well structure in Embodiment 1 of the present invention;

[0038] Among them, 1-upstream pipe section of inspection well, 2-downstream pipe section of inspection well, 3-inspection well chamber, 4-horizontal pipe, 5-vertical pipe, 6-90° elbow;

[0039] Figure 4 This is a schematic diagram of the flow field of the optimized inspection well in Embodiment 1 of the present invention;

[0040] in, Figure 4 (a) is the velocity contour plot of the cross-sectional motion. Figure 4 (b) is the velocity vector diagram of the cross-sectional motion. Figure 4 (c) is a streamline diagram of the cross-sectional motion;

[0041] Figure 5 This is a schematic diagram of the flow field of the optimized inspection well in Embodiment 2 of the present invention;

[0042] in, Figure 5 (a) is the velocity contour plot of the cross-sectional motion. Figure 5 (b) is the velocity vector diagram of the cross-sectional motion. Figure 5 (c) is a streamline diagram of the cross-sectional motion;

[0043] Figure 6 This is a schematic diagram of the flow field of the optimized inspection well in Embodiment 3 of the present invention;

[0044] in, Figure 6 (a) is the velocity contour plot of the cross-sectional motion. Figure 6 (b) is the velocity vector diagram of the cross-sectional motion. Figure 6 (c) is a streamline diagram of the cross-sectional motion;

[0045] Figure 7 The graphs show the changes in water flow and gas accumulation over time for common rainwater inspection wells in the prior art and the optimized inspection wells in Examples 1-3.

[0046] Figure 8 This is a schematic diagram of the flow field analysis method for rainwater inspection wells provided by the present invention. Detailed Implementation

[0047] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. The illustrative embodiments and descriptions of the present invention are used to explain the present invention, but are not intended to limit the present invention.

[0048] Example 1

[0049] Taking a common rainwater inspection well in existing technology as an example, its structure is as follows: Figure 1 As shown, the process of establishing a flow field analysis and optimization model is as follows:

[0050] 1. Use the SOLIDWORK modeling software built into ANSYS to create a circular rainwater straight-line inspection well flow channel model, and use the Fill function to extract the inner flow channel;

[0051] 2. Meshing, the built-in meshing software of ANSYS, was used to mesh the inner flow channel. Unstructured tetrahedral meshes were used in the inner flow channel region. An appropriate mesh size was selected, and the number of meshes was reduced to reduce computational memory. The mesh quality of the meshed file was checked using FLUENT software.

[0052] 3. Import the mesh into FLUENT software, load the turbulent energy model and flow regime model, select the VOF two-phase flow model and RNG k-ε model, and set the fluid properties to liquid water and air.

[0053] 4. Set up each inlet and outlet. Set the upstream pipe inlet face as the velocity inlet and set the water phase to gas phase ratio of 1. Set the manhole cover opening face as the velocity inlet and set the water phase to gas phase ratio of 0. Set the downstream pipe outlet face as free outflow. Define the water and gas distribution in the manhole and pipe system according to the actual water flow filling degree of the rainwater manhole and pipe system.

[0054] 5. Perform initialization settings, including setting the solution step size and iteration precision, and then perform the solution.

[0055] The initial condition setting method includes using the Region register in the Cellregisters option under Automatic mesh adaptation to divide the liquid-gas phase distribution region at the initial flow time; initializing the overall model using Initialization; defining the upper space of the inspection well as filled with air at standard atmospheric pressure and the lower space filled with water using the Phase value in the Patch function; setting the time iteration step to 0.005s and the convergence residual to 10. -5 The total number of iterations is 20,000. Check whether the convergence residual meets the requirements.

[0056] 6. Set parameters and monitor flow field characteristic contour plots to observe the flow field distribution. Import the simulation results into Tecplot and extract the velocity contour plot, velocity vector plot, and streamline plot of the cross-sectional motion. The results are as follows: Figure 2 As shown.

[0057] pass Figure 2 It is known that the water flow velocity distribution in the manhole and downstream pipe section of the existing rainwater inspection well is disordered. Specifically, the red high velocity area and the green low velocity area are randomly distributed in the velocity cloud map, and this turbulence continuously affects the water flow at the downstream end of the pipe. In addition, there is a clear velocity gradient at the downstream pipe inlet, and a large vortex is generated on the inside of the pipe bend.

[0058] To address the aforementioned issues, the structure of the inspection well needs to be optimized. The main objective is to reduce water flow turbulence in the downstream pipe section and improve flow velocity classification. Therefore, this embodiment proposes an optimized inspection well based on the data obtained from the aforementioned optimization model. A vent pipe is added between the inspection well and the pipeline, and its structure is as follows: Figure 3 As shown;

[0059] The ventilation pipe consists of a horizontal pipe (4), a vertical pipe (5), and a 90° elbow (6);

[0060] The horizontal pipe (4) is connected to the inspection well chamber (3);

[0061] The vertical pipe (5) is connected to the downstream pipe section (2) of the inspection well.

[0062] The diameter of the ventilation pipe is 0.1m.

[0063] The vertical distance 'a' between the horizontal pipe (4) and the downstream pipe section (2) of the inspection well meets the following conditions:

[0064] a = 1D

[0065] Where D is the diameter of the downstream pipe section (2) of the inspection well.

[0066] The horizontal distance b between the vertical pipe (5) and the inspection well chamber (3) meets the following conditions:

[0067] b = 5D

[0068] Where D is the diameter of the downstream pipe section (2) of the inspection well.

[0069] For the optimized rainwater inspection well structure, a new flow field analysis and optimization model was established. The specific process is as follows:

[0070] 1. Use the SOLIDWORK modeling software built into ANSYS to create a circular rainwater straight-line inspection well flow channel model, and use the Fill function to extract the inner flow channel;

[0071] 2. Meshing, the built-in meshing software of ANSYS, was used to mesh the inner flow channel. Unstructured tetrahedral meshes were used in the inner flow channel region. An appropriate mesh size was selected, and the number of meshes was reduced to reduce computational memory. The mesh quality of the meshed file was checked using FLUENT software.

[0072] 3. Import the mesh into FLUENT software, load the turbulent energy model and flow regime model, select the VOF two-phase flow model and RNG k-ε model, and set the fluid properties to liquid water and air.

[0073] 4. Set up each inlet and outlet. Set the upstream pipe inlet face as the velocity inlet and set the water phase to gas phase ratio of 1. Set the manhole cover opening face as the velocity inlet and set the water phase to gas phase ratio of 0. Set the downstream pipe outlet face as free outflow. Define the water and gas distribution in the manhole and pipe system according to the actual water flow filling degree of the rainwater manhole and pipe system.

[0074] 5. Perform initialization settings, including setting the solution step size and iteration precision, and then perform the solution.

[0075] The initial condition setting method includes using the Region register in the Cellregisters option under Automatic mesh adaptation to divide the liquid-gas phase distribution region at the initial flow time; initializing the overall model using Initialization; defining the upper space of the inspection well as filled with air at standard atmospheric pressure and the lower space filled with water using Phase value in the Patch function; setting the time iteration step to 0.005s and the convergence residual to 10. -5 The total number of iterations is 20,000. Check whether the convergence residual meets the requirements.

[0076] 6. Set parameters and monitor flow field characteristic cloud maps to observe the flow field distribution. Substitute the simulation results into Tecplot to export velocity cloud maps, velocity vector maps, and streamline diagrams for specific cross-sections. The results show that it has an improving effect on the flow pattern downstream of the inspection well, such as... Figure 4 As shown.

[0077] pass Figure 4 It can be seen that after the addition of the vent pipe, the turbulence of the water flow in the downstream pipeline is weakened, the flow velocity classification is significantly improved, and the water flow can gradually return to stability as it flows along the pipeline. This indicates that the addition of the vent pipe can effectively improve the flow pattern of the water flow in the downstream pipeline of the inspection well and reduce the energy loss caused by the turbulence of the water flow.

[0078] Example 2

[0079] This embodiment is exactly the same as Embodiment 1, except that:

[0080] An optimized inspection well is provided, with an additional vent pipe installed between the inspection well and the pipeline;

[0081] The ventilation pipe consists of a horizontal pipe (4), a vertical pipe (5), and a 90° elbow (6);

[0082] The horizontal pipe (4) is connected to the inspection well chamber (3);

[0083] The vertical pipe (5) is connected to the downstream pipe section (2) of the inspection well.

[0084] The diameter of the ventilation pipe is 0.1m.

[0085] The vertical distance 'a' between the horizontal pipe (4) and the downstream pipe section (2) of the inspection well meets the following conditions:

[0086] a = 1D

[0087] Where D is the diameter of the downstream pipe section (2) of the inspection well.

[0088] The horizontal distance b between the vertical pipe (5) and the inspection well chamber (3) meets the following conditions:

[0089] b = 8D

[0090] Where D is the diameter of the downstream pipe section (2) of the inspection well.

[0091] Based on the rainwater inspection well structure of this embodiment, a new flow field analysis and optimization model is established, and its flow field distribution is as follows: Figure 5 As shown.

[0092] Example 3

[0093] This embodiment is exactly the same as Embodiment 1, except that:

[0094] An optimized inspection well is provided, with an additional vent pipe installed between the inspection well and the pipeline;

[0095] The ventilation pipe consists of a horizontal pipe (4), a vertical pipe (5), and a 90° elbow (6);

[0096] The horizontal pipe (4) is connected to the inspection well chamber (3);

[0097] The vertical pipe (5) is connected to the downstream pipe section (2) of the inspection well.

[0098] The diameter of the ventilation pipe is 0.1m.

[0099] The vertical distance 'a' between the horizontal pipe (4) and the downstream pipe section (2) of the inspection well meets the following conditions:

[0100] a = 1D

[0101] Where D is the diameter of the downstream pipe section (2) of the inspection well.

[0102] The horizontal distance b between the vertical pipe (5) and the inspection well chamber (3) meets the following conditions:

[0103] b = 10D

[0104] Where D is the diameter of the downstream pipe section (2) of the inspection well.

[0105] Based on the rainwater inspection well structure of this embodiment, a new flow field analysis and optimization model is established, and its flow field distribution is as follows: Figure 6 As shown.

[0106] This invention also tested the changes in water flow gas accumulation over time in the common rainwater inspection wells and optimized inspection wells described in Examples 1-3, and the results are as follows: Figure 7 As shown, "1D1D" represents the horizontal distance b=1D between the vertical pipe and the manhole chamber, and the vertical distance a=1D between the horizontal pipe and the downstream pipe section of the manhole, respectively. The meanings of the other symbols are the same as above. Figure 7 It is known that in the initial stage of flow, the manholes in existing technologies require a relatively long drainage time for water to flow out of the downstream pipe. Furthermore, after a considerable period, when the flow stabilizes, a persistent airlock is easily generated at the downstream pipe inlet, hindering water flow. The model provided in this invention provides targeted optimization by adding a vent pipe. This allows water to flow quickly out of the downstream pipe after passing through the manhole in the initial stage, and once the flow stabilizes, no fixed airlock is generated, ensuring full-pipe drainage throughout the downstream pipe section.

[0107] This invention is not limited to the above embodiments. Based on the technical solutions disclosed in this invention, those skilled in the art can make some substitutions and modifications to some of the technical features without creative effort, and all such substitutions and modifications are within the protection scope of this invention.

Claims

1. A FLUENT-based rainwater inspection well flow field analysis optimization model, characterized in that, The application relates to a rainwater inspection well flow model and a preparation method thereof. Step S1, a rainwater inspection well flow model is established, and an inner flow channel structure is extracted; Step S2, the inner flow channel structure is divided by using an unstructured tetrahedral mesh, and the quality of the divided mesh is detected; Step S3, the divided mesh is imported into FLUENT software, and a turbulent energy model and a flow state model are loaded; Step S4, boundary conditions of the model in step S3 are set, water-air distribution in the rainwater inspection well and the pipeline system is defined according to the water flow fullness in the actual rainwater inspection well and the pipeline system, initialization setting is carried out, a time iteration step, iteration precision and total iteration steps are set, and calculation is carried out; Step S5, parameters and flow field characteristic cloud map monitoring are set according to the calculation results in step S4, and flow field distribution is observed. The model is used for preparing a high-discharge low-resistance rainwater inspection well; the rainwater inspection well comprises a rainwater inspection well chamber and a pipeline which are orthogonally distributed, and a vent pipe is further arranged between the rainwater inspection well chamber and the pipeline; the vent pipe is composed of a horizontal pipe (4), a vertical pipe (5) and a 90-degree elbow (6), wherein the horizontal pipe (4) is connected with the rainwater inspection well chamber (3), and the vertical pipe (5) is connected with a downstream pipe section (2) of the rainwater inspection well.

2. The FLUENT-based rainwater inspection well flow field analysis optimization model according to claim 1, characterized in that: The rainwater inspection well flow model is established by using SOLIDWORK in ANSYS; and the inner flow channel structure is extracted by using a Fill module in SOLIDWORK.

3. The FLUENT-based rainwater inspection well flow field analysis optimization model according to claim 1, characterized in that: When the inner flow channel structure is divided, a mesh size needs to be selected, and the number of meshes needs to be reduced; and the quality of the divided mesh is detected by using the FLUENT software.

4. The FLUENT-based rainwater inspection well flow field analysis optimization model according to claim 1, characterized in that: The turbulent energy model and the flow state model are respectively selected as a VOF two-phase flow model and an RNG k-epsilon model, and fluid properties are set as liquid water and air.

5. The FLUENT-based rainwater inspection well flow field analysis optimization model according to claim 1, characterized in that: The boundary condition setting process of the model is as follows: the upstream pipeline inlet surface is a velocity inlet, water phase and air phase ratios are set as 0-1, the rainwater inspection well cover opening surface is a velocity inlet, water phase and air phase ratios are set as 0-1, and the downstream pipeline outlet surface is a free outflow.

6. The FLUENT-based rainwater inspection well flow field analysis optimization model according to claim 1, characterized in that: The initialization setting process is as follows: a liquid phase-air phase distribution area is divided by using Region register at a flow initial time, the whole model is initialized by using Initialization, and a rainwater inspection well upper space is defined as being filled with air and a lower space being filled with water by using Phasevalue in a Patch function, and the pressure is standard atmospheric pressure. The time iteration step is 0.001-0.005s, and the convergence residual is <10 -5 , and the total iteration step number is >20000 steps.

7. The FLUENT-based rainwater inspection well flow field analysis optimization model according to claim 1, characterized in that: The flow field characteristic cloud map monitoring process is as follows: velocity cloud maps, velocity vector maps and flow line maps of specific section motions are extracted after model calculation results are imported into Tecplot.

8. The FLUENT-based rainwater inspection well flow field analysis optimization model according to claim 1, characterized in that: The vent pipe diameter is 0.08-0.15 m; and a vertical distance a between the horizontal pipe and the downstream pipe section of the rainwater inspection well is determined by formula 1. Formula 1: a = xD In formula 1, the value range of x is 1-2, and x is dimensionless; D is the pipe diameter of the downstream pipe section of the rainwater inspection well, and D is in the dimension of m.

9. The FLUENT-based rainwater inspection well flow field analysis optimization model according to claim 1, characterized in that: A horizontal distance b between the vertical pipe and the rainwater inspection well chamber is determined by formula 2. Formula 2: b = yD In formula 2, the value range of y is 5-10, and y is dimensionless; D is the pipe diameter of the downstream pipe section of the rainwater inspection well, and D is in the dimension of m.

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