Three-dimensional numerical simulation method for river meandering flow

Abstract

This invention discloses a three-dimensional numerical simulation method for river bend circulation. The method includes the following steps: determining the total length, width, and height of the computational field; the computational field includes the bend core area, upstream transition section, and downstream transition section; constructing the three-dimensional topography of the river channel, and then establishing a three-dimensional model of the computational field based on the determined computational field range; generating the main mesh and boundary layer mesh of the computational field; setting boundary conditions; establishing a three-dimensional numerical model of the bend circulation, including continuity equations, momentum equations, turbulence models, and a VOF model; the VOF model is used to simulate the bend circulation and capture the free surface of the river flow; converting the three-dimensional numerical model of the bend circulation into a system of linear or nonlinear algebraic equations, and then iteratively solving the algebraic equations; outputting the calculation results. This invention achieves the goals of high-precision reconstruction of river topography, efficient generation of high-quality meshes, and accurate simulation of the three-dimensional circulation structure.

Description

Technical Field

[0001] This invention relates to the field of numerical simulation technology of river hydrodynamics, specifically to a three-dimensional numerical simulation method for river bend circulation. Background Technology

[0002] Natural river bend circulation is a typical phenomenon in river dynamics. It refers to the phenomenon where, when water flows sharply through a bend, due to the inertial effect of centrifugal force, its kinetic energy is converted into potential energy at the concave bank boundary, causing a rise in water level. Under the influence of the transverse gradient, a transverse circulation is generated, forming a longitudinal spiral flow together with the longitudinal flow. The bend circulation flow field has a complex structure, including transverse circulation, vertical spiral flow, and boundary layer separation, and has a significant impact on riverbed evolution, sediment transport, and pollutant diffusion.

[0003] In existing technologies, the main research methods for river bend circulation include physical model experiments, two-dimensional simplified numerical simulation, and three-dimensional numerical simulation techniques.

[0004] Among them, physical model experiments and two-dimensional simplified numerical simulations have drawbacks such as high cost, long cycle, and difficulty in reflecting the details of three-dimensional flow fields.

[0005] Three-dimensional numerical simulation technology has been applied in river flow field research, but the following technical problems still exist: First, the accuracy of terrain modeling is insufficient: traditional methods often use regular grids or simple curved surfaces to fit river terrain, which makes it difficult to truly reflect the complex morphology of natural river channels (such as riverbed undulations, shoreline meanders, etc.). Second, the mesh generation efficiency is low: the mesh generation process for complex curved geometry is cumbersome and prone to problems such as mesh distortion or insufficient boundary layer capture, which affects the calculation accuracy. Third, the physical model is oversimplified: the three-dimensional characteristics of the bend circulation (such as the range of the calculation field, free surface fluctuations, turbulent anisotropy, etc.) are not fully considered, resulting in a large deviation between the simulation results and the measured data. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention proposes a three-dimensional numerical simulation method for river bend circulation, which can accurately reconstruct river topography, efficiently generate high-quality meshes, and accurately simulate the three-dimensional circulation structure.

[0007] To achieve the above objectives, the present invention provides a three-dimensional numerical simulation method for river bend circulation, characterized by the following steps: S1) Obtain basic data within the computational field and determine the total length, total width, and total height of the computational field; The computational field includes the core area of ​​the curve, the upstream transition section, and the downstream transition section; S2) Based on the elevation data of the river channel topography within the calculation field, construct the three-dimensional topography of the river channel, and then establish a three-dimensional model of the calculation field based on the determined scope of the calculation field. S3) Based on the established three-dimensional model of the computational field, generate the main mesh of the computational field and generate the boundary layer mesh near the riverbed; S4) Take the inlet section of the upstream transition section as the inlet boundary and set the inlet boundary as the velocity inlet; take the outlet section of the downstream transition section as the outlet boundary and set the outlet boundary as the pressure outlet. S5) Establish a three-dimensional numerical model of the bend circulation, including the continuity equation, momentum equation, turbulence model, and VOF model; the VOF model is used to simulate the bend circulation and capture the free water surface of the river flow. S6) The three-dimensional numerical model of the curved circulation is converted into a system of linear or nonlinear algebraic equations, and then the system of algebraic equations is solved iteratively. S7) Output the calculation results, which include the velocity distribution, pressure distribution, and free surface morphology data of the flow field, for analyzing the three-dimensional structural characteristics of the bend circulation.

[0008] Furthermore, in S1), the basic data includes river topographic elevation data, upstream water level, downstream water level, flow rate, average water surface width, average water depth, bend centerline radius, and bend core area arc length.

[0009] Furthermore, in S1), the total length of the computational field is calculated using the following formula. In the formula, L To calculate the total length of the field, L up The length of the upstream transition section. L bend The arc length of the core area of ​​the curve, L down The length of the downstream transition section. R The radius of the curve's centerline. n 1 , n 2 This is a length coefficient, without units. n 1 ∈ [5,10], n2 ∈ [3,5]; The total width of the computational field is calculated using the following formula. In the formula, B To calculate the total width of the field, B 0 The average width of the water surface. n 3 This is a width factor, without units. n 3 ∈ [1,3]; The total height of the computational field is calculated using the following formula. In the formula, H To calculate the total height of the field, h 0 The average water depth, n 4 This is a height coefficient, without units. n 4 ∈ [3,5].

[0010] Furthermore, in S2), SubD technology is used to construct the three-dimensional topography of the river channel, and the undulation of the riverbed and the morphology of the shoreline are accurately restored by controlling the subdivision and smoothing of the grid.

[0011] Furthermore, in S3), the main mesh of the computational field is generated through polyhedral mesh technology; and the boundary layer mesh is generated using prism layer mesh.

[0012] Furthermore, in S3), the characteristic length of the main mesh size is calculated using the following formula. In the formula, L 0 The feature length is the main mesh size. h 0 This represents the average water depth.

[0013] Furthermore, in S3), the number of boundary layers is 5 to 10.

[0014] Furthermore, in S5), the VOF model is expressed by the following formula: In the formula, F w This represents the volume fraction of water. t For time, ρ For fluid density, ν is the molecular kinetic viscosity coefficient.

[0015] Furthermore, in S6), the finite volume method is used to discretize the three-dimensional numerical model of the curved circulation, thereby converting the three-dimensional numerical model of the curved circulation into a system of linear or nonlinear algebraic equations. The specific steps include: dividing the computational field into a series of finite numbers of adjacent control volume elements using the finite volume method, with the relevant physical quantities within each control volume element precisely described by the mass conservation equation and the momentum conservation equation; calculating the values ​​of each variable at the centroid of each control volume element, and then using interpolation methods to obtain the values ​​of each variable on the surface of the control volume element; and performing surface integrals or volume integrals on each control volume element, thereby transforming the differential equations into a system of linear or nonlinear algebraic equations.

[0016] Furthermore, in S6), the SIMPLE algorithm is used to iteratively solve the system of algebraic equations. The specific solution steps include: first, assuming a pressure field, solving the momentum equation, then solving the pressure correction equation derived from the continuity equation, and thus obtaining the corrected pressure field; then updating the velocity field and pressure field, and gradually improving the hypothetical field through iteration until a convergent velocity field and pressure field are obtained.

[0017] The advantages of this invention are: 1. This invention uses SubD technology to model complex river topography, and combines polyhedral mesh and prism layer mesh technology to significantly reduce the number of elements and improve computational efficiency while ensuring mesh quality; 2. This invention couples the VOF method, NS equations, and turbulence model, which can completely capture the three-dimensional structure and free surface morphology of bend circulation, and efficiently and accurately simulate the three-dimensional complex flow field of natural river bend circulation. It is applicable to the simulation of natural river bend circulation of different scales and morphologies, and provides reliable technical support for engineering design and scientific research. The present invention provides a three-dimensional numerical simulation method for river bend circulation, which overcomes the problems of low terrain modeling accuracy, poor mesh generation efficiency, and excessive simplification of physical models in the three-dimensional numerical simulation of natural river bend circulation. It achieves the goal of high-precision restoration of river topography, efficient generation of high-quality meshes, and accurate simulation of three-dimensional circulation structure. Attached Figure Description

[0018] Figure 1 This is a flowchart of the present invention; Figure 2This is a simulated velocity distribution diagram from an embodiment of the present invention; Figure 3 This is a simulated pressure distribution diagram from an embodiment of the present invention; Figure 4 This is a simulated VOF distribution diagram from an embodiment of the present invention. Detailed Implementation

[0019] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0020] In the description of this invention, it should be understood that the terms "length," "width," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientation or positional relationships, are based on the orientation or positional relationships shown in the accompanying drawings and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on the invention. Figure 1 As shown, the present invention provides a three-dimensional numerical simulation method for river bend circulation, comprising the following steps: S1) Obtain basic data within the computational field and determine the scope of the computational field.

[0021] The scope of the computational field includes its total length, total width, and total height. The computational field includes the core area of ​​the curve, the upstream transition section, and the downstream transition section.

[0022] The basic data includes river topographic elevation data, upstream water level, downstream water level, flow rate, average water surface width, average water depth, bend centerline radius, and bend core area arc length.

[0023] The core region of the bend is the central area of ​​the entire simulation, and its function is to accurately capture and reproduce the core physical phenomenon of bend circulation. The upstream transition section is the straight channel before the water flows into the bend, and its function is to allow the water to develop a fully developed boundary layer flow state before entering the core region of the bend. The downstream transition section is the straight channel after the water flows out of the bend, and its function is to ensure the stable convergence of numerical calculations and the integrity of physical processes.

[0024] Specifically, the elevation data of the river channel topography is obtained based on survey data; the upstream water level is obtained based on hydrological data. h 1 Downstream water level h 2 ,flow Q Average width of water surface B 0 Average water depth h 0 Radius of the centerline of the curveR and the arc length of the core area of ​​the curve L bend .

[0025] The total length of the computational field includes the core area of ​​the curve and the lengths of the upstream and downstream transition sections. The total length of the computational field is calculated using the following formula. In the formula, L To calculate the total length of the field, the unit is meters. L up The length of the upstream transition section is in meters. L bend This refers to the arc length of the core area of ​​the curve, in meters. L down The length of the downstream transition section is in meters. R The radius of the curve's centerline is in meters. n 1 , n 2 This is a length coefficient, without units. n 1 ∈ [5,10], n 2 ∈ [3,5].

[0026] The total width of the computational field is widened towards both the concave and convex banks of the curve. n 3 B 0 The total width of the computational field is calculated using the following formula. In the formula, B To calculate the total width of the field, the unit is meters. B 0 The average width of the water surface, in meters. n 3 This is a width factor, without units. n 3 ∈ [1,3].

[0027] The total height of the computational field is calculated using the following formula. In the formula, H To calculate the total height of the field, the unit is meters. h 0 The average water depth is expressed in meters (m). n 4 This is a height coefficient, without units. n 4 ∈ [3,5].

[0028] This embodiment performs a three-dimensional numerical simulation of a typical natural river bend, collecting measured topographic and hydrological data of the river channel. Elevation data of the river channel are obtained through measurement and processed to obtain the river centerline; the upstream water level is determined using hydrological data. h 1 =5.2m, downstream water level h 2 =4.8m, flow rate Q =160m 3 / s; Get the average width of the water surface B 0 =20m, average water depth h 0 =5.0m, radius of the curve centerline R =50m, arc length of the core area of ​​the curve L bend =78.5m. According to the computational field determination method of the present invention, coefficients are selected... n 1 =5, n 2 =3, n 3 =1, n 4 =3, then calculate the field range: total length L =238.5m, total width B =60m, total height H =15m.

[0029] S2) Based on the elevation data of the river channel topography within the calculation field, construct the three-dimensional topography of the river channel, and then establish a three-dimensional model of the calculation field based on the scope of the calculation field determined in step S1).

[0030] Preferably, the SubD (Subdivision Surface) technology is used to construct the three-dimensional topography of the river channel, and the riverbed undulation and shoreline shape are accurately restored by controlling the subdivision and smoothing of the grid.

[0031] In this embodiment, the control grid is constructed using the river topographic elevation point data obtained in step S1), and an initial coarse grid is generated based on the elevation points. The control grid is then subdivided three times using a subdivision algorithm, and combined with smoothing technology, the resulting three-dimensional river topographic model accurately reproduces the deep channels, shallows, and tortuous shapes of the riverbed bottom, with a continuous and smooth surface and no sharp edges, laying the foundation for high-quality grid division.

[0032] S3) Generate the main mesh and boundary layer mesh.

[0033] Based on the three-dimensional model of the computational field established in step S2), the main mesh of the computational field is generated to reduce the number of elements and improve computational efficiency. A boundary layer mesh is generated near the riverbed to accurately capture the flow field characteristics near the wall.

[0034] The quality of the mesh directly determines whether the secondary flow and separation zone of the bend circulation can be accurately captured. Due to the complex topography and strong curvature of natural river channels, mesh generation must balance overall computational efficiency with analytical accuracy of near-wall flow. Therefore, it is necessary to generate a main mesh and a boundary layer mesh.

[0035] Specifically, the main mesh of the computational field is generated using polyhedral mesh technology, and the boundary layer mesh is generated using prism layer mesh.

[0036] The characteristic length of the main mesh size is calculated by the following formula. In the formula, L 0 The feature length is the main mesh size. h 0 This represents the average water depth.

[0037] In addition, the number of boundary layers is 5 to 10 to ensure that the buffer layer is crossed to enter the logarithmic law region; the growth rate is controlled between 1.1 and 1.2 to avoid excessive growth rate causing the mesh quality to deteriorate and the transition to the main mesh to be unsmooth.

[0038] In this embodiment, the characteristic length of the main mesh size L 0 =0.4m; Set a boundary layer grid on the bottom surface of the riverbed, with 8 boundary layer layers and a growth rate controlled at 1.15.

[0039] S4) Set boundary conditions.

[0040] Specifically, the inlet section of the upstream transition section is used as the inlet boundary, and the inlet boundary is set as the velocity inlet; the outlet section of the downstream transition section is used as the outlet boundary, and the outlet boundary is set as the pressure outlet.

[0041] Specifically, the upstream water level h 1 The inlet velocity at the above height is set to 0, and the upstream water level is adjusted. h 1 The average inlet velocity at the following heights is calculated using the following formula. In the formula, V upstream water level h 1 The following are the average inlet velocities at different heights, in m / s. Q The measured flow rate is expressed in cubic meters per second (m³). 3 / s, A The inlet cross-section is the water flow area, in m². 2 .

[0042] Specifically, the downstream water level h 2 The outlet pressure at the above height is set to 0, and the downstream water level is set to... h 2 The outlet pressure at the following heights is set according to the pressure distribution of the purified water.

[0043] In addition, the river topography, the perimeter and top boundaries of the computational field are set as non-slip solid walls.

[0044] In this embodiment, the upstream water level h 1 Average inlet velocity at heights below 5.0m (elevation) V = Q / A =2.0m / s.

[0045] S5) Establish a three-dimensional numerical model of the bend circulation, including the continuity equation, momentum equation, turbulence model, and VOF model.

[0046] Specifically, the fluid circulation in the bend of the river follows mass conservation and is assumed to be of constant density in the numerical simulation. The continuity equation is expressed by the following formula. In the formula, u This represents the velocity component of the fluid in the x-direction, with units of m / s. v This represents the velocity component of the fluid in the y-direction, with units of m / s. w This represents the velocity component in the z-direction of the fluid, with units of m / s.

[0047] Specifically, the fluid circulation in a river bend follows the law of conservation of momentum, which is expressed by the following equation: In the formula, ν is the molecular kinetic viscosity coefficient, with units of m. 2 / s, ν T The viscosity coefficient for turbulent motion is expressed in m. 2 / s, S u for x Source term in direction, in m / s 2 , S v for y Source term in direction, in m / s 2 , S w for z Source term in direction, in m / s 2 .

[0048] Specifically, the turbulence model adopts a two-equation k-ε model, which is expressed by the following equation: In the formula, k Turbulent kinetic energy, unit is m 2 / s 2 , ε Turbulent kinetic energy dissipation rate, in m³ 2 / s 2 , σ k The Prandtl number is the turbulent kinetic energy, which is dimensionless. σ s Prandtl number, representing the dissipation rate, is dimensionless. S k Turbulent kinetic energy k The source term, in units of m 2 / s 3 , S ε Turbulent kinetic energy ε The source term, in units of m 2 / s 3 .

[0049] In addition, a VOF model is introduced to simulate the bend circulation and capture the free water surface of the river flow.

[0050] The VOF model makes the following assumptions: First, water, air, or a mixture of the two in the same unit have the same velocity, that is, they obey the same set of momentum equations, and the volume functions of the water and air phases are treated as separate variables in the entire seepage field. Second, in any given unit, the sum of the volume fractions of water and gas equals 1, if F w If the volume fraction of water is expressed as 1-, then the volume fraction of gas is 1- F w ;when F w =1 indicates that the unit is entirely occupied by the aqueous phase; when F w =0 indicates that the cell is entirely occupied by the gas phase; when 0 < F w <1 indicates that the unit is a water-gas two-phase interface unit; Third, the variables shared by the water and gas phases, such as pressure and flow rate, are all represented by the weighted average of volume functions.

[0051] By solving the volume function, the volume fractions of water and air phases at various points in space can be obtained. In the interface region, a piecewise linear interpolation geometric reconstruction method is used to obtain the water-air interface, thereby obtaining the free liquid surface of the river flow.

[0052] The VOF model is expressed by the following formula: In the formula, F w This represents the volume fraction of water. t Time, in seconds. ρ Fluid density, in m³ 3 / s, ν is the molecular kinetic viscosity coefficient, with units of m. 2 / s.

[0053] In this embodiment, a three-dimensional numerical model of the curved circulation is established in the CFD solver, and water and air are set as incompressible fluids.

[0054] S6) Convert the three-dimensional numerical model of the curved circulation into a system of linear or nonlinear algebraic equations, and then iteratively solve the system of algebraic equations.

[0055] Preferably, the finite volume method is used to discretize the three-dimensional numerical model of the bend circulation. The pressure term adopts the PRESTO! scheme, and the momentum and turbulence terms adopt the second-order upwind scheme, thereby converting the three-dimensional numerical model of the bend circulation into a system of linear or nonlinear algebraic equations. The finite volume method uses an unstructured mesh, which is more suitable for handling problems with complex geometries.

[0056] The specific steps include: dividing the computational field into a series of finite numbers of adjacent control volume elements using the finite volume method, with the relevant physical quantities within each control volume element precisely described by the mass conservation equation and the momentum conservation equation; calculating the values ​​of each variable at the center of mass of each control volume element, and then using interpolation methods to obtain the values ​​of each variable on the surface of the control volume element; and performing surface integrals or volume integrals on each control volume element to transform the differential equations into a system of linear or nonlinear algebraic equations.

[0057] Preferably, the SIMPLE algorithm (Semi-Implicit Method for Pressure-Linked Equations) is used to iteratively solve the system of algebraic equations.

[0058] The SIMPLE algorithm is a pressure-velocity coupled algorithm for incompressible flow. The specific solution steps include: first, assuming a pressure field and solving the momentum equation, then solving the pressure correction equation derived from the continuity equation to obtain the corrected pressure field; then updating the velocity field and pressure field. These hypothetical fields are gradually improved through iteration until a convergent velocity field and pressure field are obtained.

[0059] In this embodiment, a residual convergence criterion is set, where the residuals of both the continuity equation and the momentum equation are less than 1 × 10⁻⁶. -4 The residual of the turbulence equation is less than 1×10 -5 Unsteady-state calculations (transient) were performed with a time step of 0.01 s and a simulation physical time of 100 s to ensure that the flow field evolved from the initial state to a fully developed curved circulation steady state.

[0060] S7) Output the calculation results, which include the velocity distribution, pressure distribution, and free surface morphology data of the flow field, for analyzing the three-dimensional structural characteristics of the bend circulation.

[0061] In this embodiment, after the calculation converges, the three-dimensional structural characteristics of the bend circulation are analyzed based on data such as the velocity distribution, pressure distribution, and free surface morphology of the flow field. A typical helical flow structure is observed at the bend, where the surface water flows towards the concave bank and the bottom water flows towards the convex bank, forming a transverse circulation. The free surface simulation results show that the water level on the concave bank is slightly higher than that on the convex bank, which is consistent with the "bend superelevation" phenomenon in natural river bends.

[0062] like Figure 2 The diagram shown is a velocity distribution simulation from an example. Comparing the simulated cross-sectional velocity distribution with experimental data from the actual physical model of the river channel, the velocity distribution trends are consistent, with a maximum error of less than 5%.

[0063] like Figure 3 The figure shows the pressure distribution simulated in the embodiment. The simulated pressure distribution is compared with the experimental data from the actual physical model of the river channel; the pressure distribution is close to the theoretical value.

[0064] like Figure 4 The image shows a simulated VOF distribution map from an example. Comparing the simulated VOF distribution map with experimental data from a real physical model of the river channel, the free surface is closer to the natural river channel morphology.

[0065] The above Figures 2-4 The accuracy of the three-dimensional numerical simulation method of the present invention has been verified.

[0066] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A three-dimensional numerical simulation method for river bend circulation, characterized in that, Includes the following steps: S1) Obtain basic data within the computational field and determine the total length, total width, and total height of the computational field; The computational field includes the core area of ​​the curve, the upstream transition section, and the downstream transition section; S2) Based on the elevation data of the river channel topography within the calculation field, construct the three-dimensional topography of the river channel, and then establish a three-dimensional model of the calculation field based on the determined scope of the calculation field. S3) Based on the established three-dimensional model of the computational field, generate the main mesh of the computational field and generate the boundary layer mesh near the riverbed; S4) Take the inlet section of the upstream transition section as the inlet boundary and set the inlet boundary as the velocity inlet; take the outlet section of the downstream transition section as the outlet boundary and set the outlet boundary as the pressure outlet. S5) Establish a three-dimensional numerical model of the bend circulation, including the continuity equation, momentum equation, turbulence model, and VOF model; the VOF model is used to simulate the bend circulation and capture the free water surface of the river flow. S6) The three-dimensional numerical model of the curved circulation is converted into a system of linear or nonlinear algebraic equations, and then the system of algebraic equations is solved iteratively. S7) Output the calculation results, which include the velocity distribution, pressure distribution, and free surface morphology data of the flow field, for analyzing the three-dimensional structural characteristics of the bend circulation.

2. The three-dimensional numerical simulation method for river bend circulation according to claim 1, characterized in that: In S1), the basic data includes river topographic elevation data, upstream water level, downstream water level, flow rate, average water surface width, average water depth, bend centerline radius, and bend core area arc length.

3. The three-dimensional numerical simulation method for river bend circulation according to claim 2, characterized in that: In S1), the total length of the computational field is calculated using the following formula. In the formula, L To calculate the total length of the field, L up The length of the upstream transition section. L bend The arc length of the core area of ​​the curve, L down The length of the downstream transition section. R The radius of the curve's centerline. n 1 , n 2 This is a length coefficient, without units. n 1 ∈ [5,10], n 2 ∈ [3,5]; The total width of the computational field is calculated using the following formula. In the formula, B To calculate the total width of the field, B 0 The average width of the water surface. n 3 This is a width factor, without units. n 3 ∈ [1,3]; The total height of the computational field is calculated using the following formula. In the formula, H To calculate the total height of the field, h 0 The average water depth, n 4 This is a height coefficient, without units. n 4 ∈ [3,5].

4. The three-dimensional numerical simulation method for river bend circulation according to claim 3, characterized in that: In S2), SubD technology is used to construct the three-dimensional topography of the river channel, and the undulation of the riverbed and the morphology of the shoreline are accurately restored by controlling the subdivision and smoothing of the grid.

5. The three-dimensional numerical simulation method for river bend circulation according to claim 4, characterized in that: In S3), the main mesh of the computational field is generated by using polyhedral mesh technology; the boundary layer mesh is generated by using prism layer mesh.

6. The three-dimensional numerical simulation method for river bend circulation according to claim 5, characterized in that: In S3), the characteristic length of the main mesh size is calculated by the following formula. In the formula, L 0 The feature length is the main mesh size. h 0 This represents the average water depth.

7. The three-dimensional numerical simulation method for river bend circulation according to claim 6, characterized in that: In S3), the number of boundary layers is 5 to 10.

8. The three-dimensional numerical simulation method for river bend circulation according to claim 1, characterized in that: In S5), the VOF model is expressed by the following formula: In the formula, F w This represents the volume fraction of water. t For time, ρ For fluid density, ν is the molecular kinetic viscosity coefficient.

9. The three-dimensional numerical simulation method for river bend circulation according to claim 1, characterized in that: In S6), the finite volume method is used to discretize the three-dimensional numerical model of the curved circulation, thereby converting the three-dimensional numerical model of the curved circulation into a system of linear or nonlinear algebraic equations. The specific steps include: dividing the computational field into a series of finite numbers of adjacent control volume elements using the finite volume method, with the relevant physical quantities within each control volume element accurately described by the mass conservation equation and the momentum conservation equation; calculating the values ​​of each variable at the centroid of each control volume element, and then using interpolation methods to obtain the values ​​of each variable on the surface of the control volume element; and performing surface integrals or volume integrals on each control volume element, thereby transforming the differential equations into a system of linear or nonlinear algebraic equations.

10. The three-dimensional numerical simulation method for river bend circulation according to claim 9, characterized in that: In S6), the SIMPLE algorithm is used to iteratively solve the algebraic equation system. The specific solution steps include: first, assuming a pressure field, solving the momentum equation, then solving the pressure correction equation derived from the continuity equation, and then obtaining the corrected pressure field; then updating the velocity field and pressure field, and gradually improving the hypothetical field through iteration until a convergent velocity field and pressure field are obtained.

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