A simulation method for drainage runoff and water film thickness of wide pavements under heavy rainfall based on Fluent software

Abstract

The present invention discloses a simulation method for drainage runoff and water film thickness of a wide pavement under heavy rainfall based on Fluent software, comprising the steps of: S1. determining the type of road condition to be analyzed; S2. determining the road condition data to obtain a three-dimensional model including a road model and a rainfall area model; S3. performing unstructured grid division on the three-dimensional model in step S2 to obtain a grid file; S4. importing the grid file obtained in step S3 into the Fluent solver; S5. importing rainfall data parameters into the Fluent solver; S6. exporting and post-processing the water film thickness contour map and runoff contour map of the three-dimensional model to obtain the corresponding water film thickness distribution and the size of the drainage path length; S7. comparing the calculated value of the maximum water film thickness with the water film thickness safety threshold to simulate the driving safety on rainy days. The present invention can realize the optimization of drainage for reconstructed and expanded pavements and improve driving safety.

Description

Technical Field

[0001] The present invention belongs to the field of road drainage, and particularly relates to a simulation method for drainage runoff and water film thickness of a wide-width road surface under heavy rainfall based on Fluent software. Background Art

[0002] With the continuous development of China's economy, while the highway road network is constantly improving, the route corridor resources are becoming fewer and fewer, the highway traffic flow is increasing continuously, and the requirements for highways are also getting higher and higher. The original two-way four-lane and six-lane highways have gradually been widened to eight lanes and above in both directions due to their inability to meet the increasing demand for traffic flow, greatly improving the occurrence of traffic congestion. Therefore, with the increase in the construction of reconstructed and expanded and ultra-wide lane highways, the proportion of wide-width highways is gradually increasing. In rainy areas, the drainage efficiency of highways has always been the focus of road surface design. With the increase in the road width after reconstruction and expansion, the drainage path length of the road has also increased, and the road surface water cannot be discharged from the road surface in time, resulting in road surface water accumulation at long longitudinal slope sections, the bottom of concave vertical curves, superelevation transition sections, interchange merging and diverging sections, etc. This not only easily causes the phenomenon of "water floating" for vehicles driving at high speeds, but also the high-speed rotating wheels will atomize the rainwater, blocking the driver's line of sight and bringing great potential safety hazards to driving. At the same time, the infiltration of road surface water will also cause uneven settlement of the roadbed and exacerbate the cracking of the road surface structure, thereby reducing the strength and stability of the road surface structure, affecting driving safety, shortening the road surface life, and increasing the road surface management and maintenance costs.

[0003] However, existing theoretical calculation methods mostly use the finite difference method and multiple linear regression, and mostly analyze the calculation models of normal road widths, which are not applicable to simulating the drainage path and water film thickness distribution of wide-width road surfaces under heavy rainfall. The calculation steps are complex, the reliability is low, and visualization is not possible. Field tests not only require a large experimental site and are difficult to accurately simulate the rainfall intensity, but also the methods for measuring the water film thickness on the road surface mainly include manual measurement using a scale or infrared spectroscopy detection method. The manual detection method consumes human resources, is greatly affected by human subjectivity, has certain errors and is difficult to ensure accuracy; the infrared spectroscopy detection method is greatly affected by site factors and air media, and the accuracy cannot be guaranteed either. Summary of the Invention

[0004] The purpose of the present invention is to provide a simulation method for drainage runoff and water film thickness of a wide-width road surface under heavy rainfall based on Fluent software, and to form a comprehensive road drainage system design scheme based on the allowable drainage path length of the road surface and the corresponding geometric alignment design indicators, so as to realize the optimization of drainage for reconstructed and expanded road surfaces and improve driving safety.

[0005] The purpose of the present invention can be achieved through the following technical solutions.

[0006] A simulation method for drainage runoff and water film thickness on a wide road surface under heavy rainfall based on Fluent software, comprising the following steps:

[0007] S1. Determine the type of road conditions to be analyzed;

[0008] S2. According to the road condition data determined in step S1, use 3D modeling software to perform 1:1 modeling on the road under the corresponding conditions to obtain a three-dimensional model including a road model and a rainfall area model;

[0009] S3. Perform unstructured grid division on the three-dimensional model in step S2 and encrypt the grids around the three-dimensional model to improve the calculation accuracy, and obtain a grid file;

[0010] S4. Import the grid file obtained in step S3 into the Fluent solver, and set the components, calculation model, algorithm, and boundary conditions. Solve the road model and the rainfall area model in the grid file. The discrete phase model (DPM model) in the Fluent solver is used to simulate the rainfall, and the Eulerian water film model (EWF model) is used to simulate the runoff formed after raindrop particles fall on the road surface. The road model in the network file is set as the wall boundary condition, the top of the rainfall area model in the grid file is set as the velocity inlet, and the rest of the rainfall area model in the grid file is set as the pressure outlet;

[0011] S5. Import rainfall data parameters into the Fluent solver, determine the rainfall intensity, raindrop size, and rainfall duration, start simulating the rainfall process after initializing the simulation until the runoff that changes dynamically with time is obtained through convergence calculation. When the residual value is lower than 0.0001, it is considered convergent;

[0012] S6. Export and post-process the water film thickness contour map and runoff contour map of the three-dimensional model to obtain the corresponding water film thickness distribution and the size of the drainage path length;

[0013] S7. According to the drainage path length contour map and the water film thickness contour map, compare the calculated value of the maximum water film thickness with the water film thickness safety threshold. When the calculated value of the maximum water film thickness is greater than the water film thickness safety threshold, it indicates that the road condition does not meet the safety requirements for driving in rainy days.

[0014] Based on a large amount of rainy-day traffic accident data and verification of the measured water film thickness, a calculation method for the water film thickness safety threshold is obtained:

[0015] d = (1.449 - 0.158v 0.983 p -0.489 )μ 0.794 T 0.978 ×1.821

[0016] Where d is the water film thickness threshold to ensure driving safety, in mm, v is the vehicle speed, in m / s; p is the tire pressure, in kPa; T is the construction depth, in mm; μ is the road skid resistance coefficient, dimensionless;

[0017] S8. Adjust the longitudinal slope and superelevation gradient of the linear indicators until the water film thickness meets the safety threshold. If changing the linear indicators cannot make the water film thickness meet the safety requirements, it is necessary to solve the water accumulation problem by paving drainage pavement and setting up drainage facilities in the corresponding areas where the water film thickness exceeds the safety threshold.

[0018] The present invention also has the following preferred design:

[0019] The 3D modeling software used in step S2 of the present invention is Space Claim, which is a natural 3D design system and can be abbreviated as SCDM.

[0020] The three-dimensional model of the present invention is composed of a road model and a rainfall area model that share topology. The rainfall area is constructed in a rectangular parallelepiped manner. After the road model and the rainfall area are shared topologically, the boundary condition of the road model is determined.

[0021] The rainfall simulation of the DPM model of the present invention is as follows:

[0022] 1) The flow input is stable and consistent with the set rainfall intensity;

[0023] 2) Completely cover the surface of the road geometry model and be evenly distributed;

[0024] 3) Use granular method to restore the rainfall process;

[0025] 4) Controllable rainfall duration.

[0026] The present invention uses the EWF model to simulate road surface runoff, that is, to simulate the flow of road surface rainwater runoff, the distribution of water film thickness in various areas of the road, etc., including:

[0027] 1) It can be coupled with the DPM model to collect DPM fluid particles and form a water film on the surface of the road geometry model;

[0028] 2) It can simulate the flow of road surface runoff and track the water film in the selected area, which gathers to form runoff under the action of gravity, surface tension, etc., and flows out of the road width and dissipates;

[0029] 3) It can intuitively reflect the distribution of water depth on the road surface at different locations in the form of water film thickness.

[0030] The unstructured grid division of the three-dimensional model of the present invention includes the following steps: The grid division uses the pipeline working mode in FluentMeshing, that is, the Fluent grid division tool. First, import the three-dimensional model, then add local dimensions, set the target grid size of the wall boundary to 0.05 m. In the surface grid settings, set the global minimum size to 0.05 m, the growth rate to 1.2, and keep the rest of the settings default. In the description of geometric structure settings, select that the model consists only of a fluid region without voids, and select no for all other settings. Then update the region type setting, set the region type to fluid, that is, fluid characteristics, and do not add a boundary layer. After that, generate the volume grid.

[0031] The steps for the simulation analysis of the three-dimensional model of the present invention include:

[0032] Use the pressure-based type, absolute velocity format, transient analysis, and the gravity is in the negative z-axis direction;

[0033] Enable DPM tracking, adjust the maximum number of steps to 5000 in the discrete phase settings, select to interact with the continuous phase, select random collision, aggregation, and fragmentation in the physical model. In the injection source settings, select the surface incidence form, determine the particle size and flow rate according to the local rainfall, set the time according to the research rainfall duration, set it to vertical incidence. On the basis of simulating rainfall using the DPM model, enable the EWF model on the model wall to collect raindrops and form surface runoff. In practical applications, check solve momentum, that is, solve momentum and DPM collection, that is, collect the raindrop particles generated by DPM, and consider the gravity and the surface pressure of the liquid film in the vector options. Select liquid water for the liquid film material, and the surface tension coefficient is 0.07194 n / m. For the discretization of time, continuity, and vectors, use first-order explicit. To improve the calculation accuracy, the time step size for the initial calculation is taken as 0.01 s;

[0034] In the initialization module, select the raindrop incidence surface as the calculation reference position, and then start the operation. The number of time steps and the step size depend on the research. The more steps, the more stable the surface runoff is. The more step sizes, the more rainfall details can be seen. After the calculation is completed, obtain the contour maps of the drainage path length and the water film thickness distribution in the contour map module.

[0035] The present invention has the following beneficial effects:

[0036] In the present invention, fluent is used to simulate the water film thickness and drainage path length of the reconstructed and expanded wide - width road surface, quantify traffic safety problems, which helps designers complete the digital identification and recording of the water film thickness and drainage path length. By comparing the calculated value of the maximum water film thickness with the water film thickness threshold, it is judged whether the working condition meets the drainage requirements, explore the drainage path length threshold, and on this basis, study the geometric linear index design of the reconstructed and expanded wide - width road under the allowable drainage path length. In addition, the numerical values of the water film thickness and drainage path length obtained in the present invention can truly reflect the accumulation of rainwater on the road, which is beneficial to determining the braking distance and vehicle handling index, providing reference and basis for traffic safety design. Brief Description of the Drawings

[0037] Figure 1 is the road model in the embodiment;

[0038] Figure 2 is the three - dimensional model for simulation in the embodiment;

[0039] Figure 3 is the boundary condition of the three - dimensional model for simulation in the embodiment;

[0040] Figure 4 is the software screenshot of importing the three - dimensional model and adding local dimensions in the mesh generation step of the embodiment Figure 1 ;

[0041] Figure 5 is the software screenshot of generating surface network and describing geometric structure in the mesh generation step of the embodiment Figure 2 ;

[0042] Figure 6 is the software screenshot of updating region type setting and mesh refinement in the mesh generation step of the embodiment Figure 3 ;

[0043] Figure 7 is the schematic diagram of the mesh body of the three - dimensional model meshing in the embodiment;

[0044] Figure 8 is the software screenshot of importing the solution mode in the embodiment Figure 4 ;

[0045] Figure 9 is the software screenshot of setting raindrop particles in the embodiment Figure 5 ;

[0046] Figure 10 is the software screenshot of setting the injection source in the embodiment Figure 6 ;

[0047] Figure 11 is the software screenshot of boundary condition setting in the embodiment Figure 7 ;

[0048] Figure 12 is the software section set by the initialization module in the embodiment Figure 8 ;

[0049] Figure 13 is the software section for solving and running calculations in the embodiment Figure 9 ;

[0050] Figure 14 is the 3D model of the straight road section simulation;

[0051] Figure 15 is the contour map of the water film thickness distribution of the straight road section;

[0052] Figure 16 is the contour map of the drainage path distribution of the straight road section;

[0053] Figure 17 is the 3D model of the circular curve road section simulation;

[0054] Figure 18 is the contour map of the water film thickness distribution of the circular curve road section;

[0055] Figure 19 is the contour map of the drainage path distribution of the circular curve road section;

[0056] Figure 20 is the 3D model of the S-shaped curve road section simulation;

[0057] Figure 21 is the contour map of the water film thickness distribution of the S-shaped curve road section;

[0058] Figure 22 is the contour map of the drainage path distribution of the S-shaped curve road section. Specific implementation manner

[0059] The following combines the accompanying drawings and embodiments to detail the technical solutions of the present invention, so that those of ordinary skill in the art can better understand and implement the technical solutions of the present invention.

[0060] As Figures 1 to 13 shown, a simulation method for drainage runoff and water film thickness of a wide-width road surface under heavy rainfall based on fluent software includes the following steps:

[0061] S1. Determine the type of road condition to be analyzed;

[0062] S2. According to the road condition data determined in step S1, use 3D modeling software to perform 1:1 modeling of the road corresponding to the condition to obtain a 3D model including a road model and a rainfall area model, where the road model is as Figure 1 shown, and the 3D model is as Figure 2 shown;

[0063] S3. Unstructured mesh division is performed on the three-dimensional model in step S2, and the mesh around the three-dimensional model is encrypted to improve the calculation accuracy, obtaining a mesh file. Specifically, the unstructured mesh division of the three-dimensional model is as Figures 4 to 7 shown, including the steps: The mesh division uses the pipeline working mode in Fluent Meshing, that is, the Fluent mesh division tool. First, the three-dimensional model is imported, then local dimensions are added. The target mesh size of the wall boundary is set to 0.05 m. In the surface mesh settings, the global minimum size is set to 0.05 m, the growth rate is set to 1.2, and the rest of the settings remain default. In the description of geometric structure settings, it is selected that the model consists only of a fluid region without voids, and the rest of the settings are all set to no. Then the region type setting is updated, and the region type is set to fluid, that is, fluid characteristics, and no boundary layer is added. After that, the volume mesh is generated;

[0064] S4. As Figures 8 to 11 shown, the mesh file obtained in step S3 is imported into the Fluent solver, and the components, calculation model, algorithm, and boundary conditions are set. The road model and rainfall area model in the mesh file are solved. The discrete phase model in the Fluent solver, that is, the DPM model, is used to simulate rainfall, and the Eulerian wall film model, that is, the EWF model, is used to simulate the runoff formed after raindrop particles fall on the road surface. The road model in the network file is set to the wall boundary condition, the top of the rainfall area model in the mesh file is set to the velocity inlet, and the rest of the rainfall area model in the mesh file is set to the pressure outlet, as Figure 3 shown;

[0065] S5. Rainfall data parameters are imported into the Fluent solver, the rainfall intensity, raindrop size, and rainfall duration are determined. After the simulation is initialized, the rainfall process is simulated until the calculation converges to obtain the runoff that changes dynamically with time. When the residual value is lower than 0.0001, it is considered convergent;

[0066] S6. The water film thickness contour map and runoff contour map of the three-dimensional model are exported for post-processing to obtain the corresponding water film thickness distribution and the size of the drainage path length;

[0067] S7. According to the drainage path length contour map and the water film thickness contour map, the calculated value of the maximum water film thickness is compared with the water film thickness safety threshold. When the calculated value of the maximum water film thickness is greater than the water film thickness safety threshold, it indicates that the road condition does not meet the safety requirements for driving in rainy days.

[0068] Based on a large amount of rainy-day traffic accident data and actual measured water film thickness verification, the calculation method of the water film thickness safety threshold is obtained:

[0069] d = (1.449 - 0.158v0.983 p -0.489 )μ 0.794 T 0.978 ×1.821

[0070] Where d is the water film thickness threshold to ensure driving safety, in mm, v is the vehicle speed, in m / s; p is the tire pressure, in kPa; T is the construction depth, in mm; μ is the road skid resistance coefficient, dimensionless;

[0071] S8. Adjust the longitudinal slope and superelevation gradient of the linear indicators until the water film thickness meets the safety threshold. If changing the linear indicators cannot make the water film thickness meet the safety requirements, it is necessary to solve the water accumulation problem by paving drainage pavement and setting up drainage facilities in the corresponding areas where the water film thickness exceeds the safety threshold.

[0072] As a preferred embodiment:

[0073] The 3D modeling software used in step S2 is Space Claim, which is a natural way 3D design system, which can be abbreviated as SCDM.

[0074] The simulated three-dimensional model is composed of a road model and a rainfall area model that share topology. The rainfall area is constructed in the form of a rectangular parallelepiped. After the road model and the rainfall area are shared topologically, the boundary conditions of the road model are determined.

[0075] The rainfall simulation of the DPM model is as follows:

[0076] 1) The flow input is stable and consistent with the set rainfall intensity;

[0077] 2) Completely cover the surface of the road geometry model and be evenly distributed;

[0078] 3) Use granular method to restore the rainfall process;

[0079] 4) Controllable rainfall duration.

[0080] The EWF model is used to simulate road surface runoff, that is, to simulate the flow of road surface rainwater runoff and the distribution of water film thickness in various areas of the road, including:

[0081] 1) It can be coupled with the DPM model to collect DPM fluid particles and form a water film on the surface of the road geometry model;

[0082] 2) It can simulate the flow of road surface runoff and track the water film in the selected area, which gathers to form runoff under the action of gravity, surface tension, etc., and flows out of the road width and dissipates;

[0083] 3) It can intuitively reflect the distribution of water depth on the road surface at different locations in the form of water film thickness.

[0084] The steps for simulating and analyzing the 3D model of the present invention include:

[0085] Use the pressure-based type, absolute velocity format, transient analysis, with gravity in the negative z-axis direction;

[0086] Turn on DPM tracking. In the discrete phase settings, adjust the maximum number of steps to 5000, select interaction with the continuous phase, choose random collision, aggregation, and breakup for the physical model. In the injection source settings, select the surface incidence form, determine the particle size and flow rate according to the local rainfall, set the time according to the studied rainfall duration, set it as vertical incidence. On the basis of simulating rainfall using the DPM model, turn on the EWF model on the model wall to collect raindrops and form surface runoff. In practical applications, check solve momentum and DPM collection to solve momentum and collect raindrop particles generated by DPM, and consider gravity and the surface pressure of the liquid film in the vector options. Select liquid water for the liquid film material, with a surface tension coefficient of 0.07194 n / m. For the discretization of time, continuity, and vectors, use first-order explicit. To improve the calculation accuracy, the time step for the initial calculation is taken as 0.01 s;

[0087] As Figure 12 and Figure 13 shown, in the initialization module, select the calculation reference position on the raindrop incidence surface, and then start the operation. The number of time steps and the step size are determined according to the study. The more steps, the more stable the surface runoff. The more step sizes, the more rainfall details can be seen. After completing the calculation, obtain the contour map of the drainage path length and water film thickness distribution in the contour map module.

[0088] Simulation calculation example 1:

[0089] As Figure 14 shown, this example is a 3D model of a straight road section. The design speed of this straight road section is 100 km / h, the length is 300 m, the width is 18.75 m, the cross slope is 2%, and the longitudinal slope is 1%.

[0090] Figure 15 The contour map of the water film thickness distribution obtained from the transient calculation is shown. It can be seen that the lateral distribution of the water film thickness on the road model shows a certain pattern. The water film thickness value is lower on the inner side of the road and higher on the outer side of the road, reaching 3.24 mm, which basically conforms to the actual situation.

[0091] Figure 16 The contour map of the drainage path obtained from the simulation is shown. It can be seen that the drainage path of the straight road section is linear. After measurement, the maximum drainage path length is 16.23 m.

[0092] The calculated safety threshold of the water film thickness corresponding to the straight-line section condition is 8.26 mm. By comparison, it is found that the calculated maximum water film thickness in Example 1 is 3.24 mm, which is lower than the safety threshold of the water film thickness. Therefore, it can be determined that the linear combination of the straight-line section with a design speed of 100 km / h, a length of 300 m, a width of 18.75 m, a cross slope of 2%, and a longitudinal slope of 1% can meet the road drainage requirements in the design, and the corresponding drainage path length threshold is 16.23 m.

[0093] Simulation calculation Example 2:

[0094] As Figure 17 shown, this example is a three-dimensional model of the circular curve section condition. The design speed of this circular curve section is 100 km / h, the length is 300 m, the width is 18.75 m, the radius is 4500 m, the superelevation cross slope is 2%, and the longitudinal slope is 0.5%.

[0095] Figure 18 The contour map of the water film thickness distribution obtained by transient calculation is shown. It can be seen that the lateral distribution of the water film thickness on the road model shows a certain pattern. The water film thickness value is lower at the higher road elevation and higher at the lower road elevation, reaching 3.42 mm, which basically conforms to the actual situation.

[0096] Figure 19 The drainage path contour map obtained by simulation is shown. It can be seen that due to the single combined slope of the circular curve section, the drainage path is linear. After measurement, the maximum drainage path length is 19.32 m.

[0097] The calculated safety threshold of the water film thickness corresponding to the condition in Example 2 is 8.26 mm. By comparison, it is found that the calculated maximum water film thickness in Example 2 is 3.42 mm. Therefore, it can be determined that the linear combination of the circular curve section with a design speed of 100 km / h, a length of 300 m, a width of 18.75 m, a radius of 4500 m, a superelevation cross slope of 2%, and a longitudinal slope of 0.5% can meet the road drainage requirements in the design, and the corresponding drainage path length threshold is 19.32 m.

[0098] Simulation calculation Example 3:

[0099] As Figure 20 shown, this example is a three-dimensional model of the S-shaped curve section. The design speed of this S-shaped curve section is 100 km / h, the length is 223 m, the width is 18.75 m, the superelevation at the starting point of the transition section is 2%, the superelevation at the ending point of the transition section is -2%, the longitudinal slope is 1%, and the superelevation transition rate is 1 / 330.

[0100] Figure 21It shows the contour map of the water film thickness obtained from transient calculations. It can be seen that in the area with a higher water film thickness, it covers the entire width of the road horizontally, and the maximum water film thickness value appears on the inner side of the road, reaching 8.48 mm. This is related to the changing state of the combined road gradient and basically conforms to the actual situation.

[0101] Figure 22 It shows the contour map of the drainage path obtained from simulation. It can be seen that the drainage path of the S-shaped curve section is arc-shaped. After measurement, the maximum drainage path length is 91.32 m.

[0102] It is calculated that the safety threshold of the water film thickness corresponding to the working condition in Example 3 of this case is 8.26 mm. By comparison, it is found that the calculated value of the water film thickness is higher than the safety threshold of the water film thickness, and the safety of driving in rainy days cannot be guaranteed. Therefore, it can be determined that the S-shaped curve linear combination with a design speed of 100 km / h, a length of 223 m, a width of 18.75 m, a superelevation of 2% at the start of the transition section, a superelevation of -2% at the end of the transition section, a longitudinal slope of 1%, and a superelevation transition rate of 1 / 330 cannot meet the road drainage requirements in the design. It is necessary to adjust the linear indexes such as the longitudinal slope and the superelevation transition rate until the water film thickness meets the safety threshold. If changing the linear indexes cannot make the water film thickness meet the safety requirements, it is necessary to solve the water accumulation problem by laying a drainage pavement and setting drainage facilities in the corresponding areas where the water film thickness exceeds the safety threshold.

[0103] The above embodiments are only relatively preferred embodiments of the present invention, but they cannot be used as a limitation to the invention. Any variations and improvements made based on the concept of the present invention shall fall within the protection scope of the present invention. The specific protection scope shall be subject to the description in the claims.

Claims

1. A simulation method for drainage runoff and water film thickness of wide roads under heavy rainfall based on Fluent software, characterized in that, The steps include: S1. Determine the type of road condition that needs to be analyzed; S2. According to the road condition data determined in step S1, a 1:1 modeling of the road of the corresponding condition is performed using 3D modeling software to obtain a three-dimensional model including a road model and a rainfall area model; S3. Performing unstructured meshing on the three-dimensional model in step S2 and encrypting the mesh around the three-dimensional model to improve calculation accuracy, thereby obtaining a mesh file; S4. Import the grid file obtained in step S3 into the Fluent solver, set the components, calculation model, algorithm and boundary conditions, solve the road model and rainfall area model in the grid file, the solution model uses the discrete phase model, i.e., the DPM model, in the Fluent solver to simulate rainfall, and uses the Euler liquid film model, i.e., the EWF model, to simulate the runoff formed after raindrop particles fall on the road surface, the road model in the grid file is set as the wall boundary condition, the top of the rainfall area model in the grid file is set as the velocity inlet, and the rest of the rainfall area model in the grid file is set as the pressure outlet; S5. Import rainfall data parameters into the Fluent solver, determine rainfall intensity, raindrop size, and rainfall duration, initialize the simulation, and start simulating the rainfall process until the calculation converges to obtain the runoff that changes dynamically over time. When the residual value is less than 0.0001, it is considered converged; S6. The water film thickness cloud map and the runoff cloud map of the three-dimensional model are exported and processed to obtain the corresponding water film thickness distribution and drainage path length; S7. Compare the calculated maximum water film thickness value with the water film thickness safety threshold value based on the drainage path length cloud map and the water film thickness cloud map. When the calculated maximum water film thickness value is greater than the water film thickness safety threshold value, it indicates that the road condition does not meet the driving safety requirements in rainy days. Based on a large amount of rainy day traffic accident data and actual water film thickness verification, the calculation method of the water film thickness safety threshold is obtained: d = (1.449 - 0.158v 0.983 p -0.489 )μ 0.794 T 0.978 × 1.821 Where d is the water film thickness threshold to ensure driving safety, in mm, v is the vehicle speed, in m / s; p is the tire pressure, in kPa; T is the construction depth, in mm; μ is the road skid resistance coefficient, dimensionless; S8. Adjust the longitudinal slope and superelevation gradient of the linear indicators until the water film thickness meets the safety threshold. If changing the linear indicators cannot make the water film thickness meet the safety requirements, it is necessary to solve the water accumulation problem by paving drainage pavement and setting up drainage facilities in the corresponding areas where the water film thickness exceeds the safety threshold.

2. A simulation method for wide - width road surface drainage runoff and water film thickness under heavy rainfall based on Fluent software according to claim 1, characterized in that: The 3D modeling software used in step S2 is Space Claim.

3. The simulation method for wide - width road surface drainage runoff and water film thickness under heavy rainfall based on Fluent software according to claim 2, wherein: The three-dimensional model is composed of a road model and a rainfall area model that share topology. The rainfall area is constructed in a rectangular parallelepiped manner. After the road model and the rainfall area are shared topologically, the boundary condition of the road model is determined.

4. A simulation method for wide - width road surface drainage runoff and water film thickness under heavy rainfall based on Fluent software according to claim 3, characterized in that, The rainfall simulation of the DPM model is as follows: 1) The flow input is stable and consistent with the set rainfall intensity; 2) Completely cover the surface of the road geometry model and be evenly distributed; 3) Use granular method to restore the rainfall process; 4) Controllable rainfall duration.

5. A simulation method for wide - width road surface drainage runoff and water film thickness under heavy rainfall based on Fluent software according to claim 4, characterized in that: The EWF model is adopted to simulate the road surface runoff, that is, to simulate the flow of rainwater runoff on the road surface, the distribution of water film thickness in each area of the road, etc., including: 1) It can be coupled with the DPM model for calculation, collect DPM fluid particles and form a water film on the surface of the road geometric model; 2) It can simulate the flow of road surface runoff, track the water film in the selected area, and converge to form runoff under the action of gravity, surface tension, etc., and flow out of the road width and dissipate; 3) It can intuitively reflect the distribution of road surface ponding depth at different positions in the form of water film thickness.

6. A simulation method for wide - width road surface drainage runoff and water film thickness under heavy rainfall based on Fluent software according to any one of claims 1 to 5, characterized in that, The unstructured grid division of the three-dimensional model includes the steps: The grid division uses the pipeline working mode in Fluent Meshing. First, import the three-dimensional model, then add local dimensions, set the target grid size of the wall boundary to 0.05m. In the surface grid settings, set the global minimum size to 0.05m, the growth rate to 1.2, and the rest of the settings to default. In the description of geometric structure settings, select that the model consists only of fluid regions without voids, and select no for all other settings. Then update the region type setting, set the region type to fluid, that is, fluid characteristics, do not add a boundary layer, and then generate volume grids.

7. A simulation method for wide - width road surface drainage runoff and water film thickness under heavy rainfall based on Fluent software according to claim 6, characterized in that, The steps of the simulation analysis of the three-dimensional model include: Use the pressure-based type, absolute velocity format, transient analysis, and the gravity is in the negative direction of the z-axis; Turn on DPM tracking, adjust the maximum number of steps to 5000 in the discrete phase settings, select to interact with the continuous phase, select random collision, aggregation, and fragmentation in the physical model. In the injection source settings, select the surface incidence form, determine the particle size and flow rate according to the local rainfall, set the time according to the research rainfall duration, set it to vertical incidence. On the basis of simulating rainfall using the DPM model, turn on the EWF model on the model wall to collect raindrops and form road surface runoff. In practical applications, check solve momentum, that is, solve momentum and DPM collection, that is, collect the raindrop particles generated by DPM, and consider gravity and surface pressure of the liquid film in the vector options. The liquid film material is selected as liquid water, and the surface tension coefficient is 0.07194n / m. For the discretization of time, continuity, and vectors, first-order explicit is used. To improve the calculation accuracy, the time step of the initial calculation is taken as 0.01s; In the initialization module, select the calculation reference position on the raindrop incidence surface, and then start the operation. The number of time steps and step size depend on the research. The more steps, the more stable the road surface runoff tends to be. The more step sizes, the more rainfall details can be seen. After the calculation is completed, obtain the cloud diagram of the drainage path length and water film thickness distribution in the cloud diagram module.

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