CN114925624A - Natural river channel three-dimensional water flow numerical simulation method - Google Patents
Natural river channel three-dimensional water flow numerical simulation method Download PDFInfo
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Abstract
The invention discloses a three-dimensional water flow numerical simulation method of a natural river channel, which is characterized in that gridding software is firstly adopted to carry out three-dimensional gridding division on a natural river channel calculation domain; then starting FLUENT software, and guiding the three-dimensional grid of the natural river channel into a three-dimensional calculation module of the FLUENT software; selecting a pressure-based separation type solver solution, determining a water-gas two-phase flow-based VOF calculation model and a K-epsilon turbulence model, and setting material parameters, an operation environment and boundary conditions; adjusting parameters set for controlling the solution; initializing a flow field and solving; and finally, displaying and outputting a calculation result to obtain water flow characteristic parameters including a speed field and a pressure field. The method can better realize the three-dimensional space subdivision of the complex shape of the natural river channel, so that the method can better complete the three-dimensional water flow numerical simulation of the river channel, does not need to carry out coordinate transformation on a water flow control equation, and improves the accuracy and the stability of the three-dimensional water flow numerical simulation of the natural river channel.
Description
Technical Field
The invention relates to the technical field of computational fluid mechanics calculation of natural river channels, in particular to a numerical simulation method for three-dimensional water flow of a natural river channel with irregular width.
Background
In engineering construction such as channel improvement, river regulation, hydropower development and the like, three-dimensional water flow numerical simulation of a natural river is usually required to be carried out so as to obtain a velocity field, a pressure field, a water surface line, even turbulent kinetic energy k and turbulent kinetic energy dissipation rate epsilon distribution in the river, and the three-dimensional water flow numerical simulation is used for guiding engineering design and management.
At present, the numerical simulation of the hydrodynamic force of the natural riverway is mainly focused on one-dimensional and two-dimensional models. CN114091163A discloses a river channel structure overflowing numerical simulation method based on a finite volume method. Firstly, acquiring plane geometric data, river section data and structure geometric dimensions of a river channel, wherein the river channel adopts one-dimensional finite volume unit dispersion, a hydraulic power element value is stored in a unit center, and the position of a structure is a unit interface. Calculating the water quantity passing through the structure interface in each time step according to a structure overflowing formula, deducting and increasing the water quantity in an upstream unit and a downstream unit adjacent to the interface by adopting a source item processing method, reconstructing a hydraulic element value at the structure interface by adopting a non-reflection boundary condition to ensure the continuity of calculation, and further calculating the numerical flux at the structure interface. The method can accurately reflect the overflowing characteristics of each structure, simultaneously ensure the accuracy and stability of the integral calculation of the one-dimensional river flow model, and provide a new solution for the overflowing treatment of the structures under the numerical frame of the one-dimensional finite volume method. CN114117609A relates to a method and device for treating a navigation channel, the device comprises: measuring the underwater topography of a river mouth by adopting an RTK (real-time kinematic) matched with a multi-beam sounding system, determining the geographic position coordinates of a doorsill according to the topography, and analyzing the characteristics of the underwater topography; a water-sand two-phase numerical simulation system is utilized to build a two-dimensional hydrodynamic model according to the underwater topography of the river mouth; calculating a background flow field by using a two-dimensional hydrodynamic model, and determining water depth and mainstream distribution characteristics; determining the dredging range and the dredging scale of the sediment of the check sand bank according to the water depth and the main flow distribution characteristics by combining with the channel design indexes; simulating a dredging effect by using a two-dimensional hydrodynamic model according to a runoff dynamic condition, a mechanical disturbance parameter and an engineering layout, and optimizing a dredging range and a dredging scale; and selecting the type of the dredging ship and the number of the ships for the sediment mechanical disturbance according to the optimized dredging range and the dredging scale so as to carry out dredging treatment by the ships.
The three-dimensional hydrodynamic numerical simulation calculation domain is generally regular in size and convenient for mesh generation, and the application of three-dimensional water flow number simulation of a natural river channel is greatly limited due to the facts that the surface of the natural river channel is uneven, the width and the depth are different, the shoreline is bent, the overall solid shape of the river channel is extremely irregular, and the mesh generation is very difficult. CN113627050A provides a method for optimizing a river channel scouring undercut treatment scheme, the whole method is based on Fluent software, numerical simulation is carried out on the whole river channel only before the river channel undercut treatment scheme is implemented, river channel water flow state analysis, river channel and protective building pressure analysis and protective building shear stress analysis are carried out on the simulation result, and scheme optimization is guided according to the analysis result. The method changes the engineering problem of optimizing the river bed scouring undercut treatment scheme into a mathematical problem by utilizing the powerful property of Revit modeling, the high quality of hypermesh division grids, the advanced fluid numerical simulation method of Fluent and the intuitiveness of Post-processing of Tecplot or CFD-Post simulation results. By adopting the simulation technology, a river channel model consistent with an actual system is established, the riverbed scouring undercut treatment is simulated, structural parameters of a riverbed treatment building are optimized according to a simulation result, and optimization guidance is provided for a riverbed scouring undercut treatment scheme. The method uses hypermesh software to effectively divide the grids of the natural river channel edge-beach shallow area, and meanwhile, the number of grid nodes in the water depth direction is too small, so that an ideal simulation effect is difficult to obtain in the aspects of calculating the accuracy of the water surface line and the speed field. CN112784505A discloses a river three-dimensional flow field data processing method based on numerical-analytic combined solution, wherein in the solution process, a longitudinal grid of the river needs to be split, and on the longitudinal section of the river, the cross sectional area, water level, flow and water level gradient of each section of the upstream and downstream of the river are calculated by numerical simulation; calculating and calculating to obtain a three-dimensional flow field structure of the cross section of the river channel according to a three-dimensional analysis model of the cross section by taking the calculated water level and flow as boundary conditions on the cross section to be solved and the moment based on the user specified conditions; and integrating the calculation result and the cross section three-dimensional analysis model result to obtain a three-dimensional flow field calculation result. The invention can save a large amount of calculation time; the cross section three-dimensional calculation result can be independently output according to the driving factor, so that the result can be conveniently analyzed by a practitioner; the model adopts a blocking design, and the numerical model and the analysis model are relatively independent, so that the secondary development of a user is facilitated. According to the method, the water level, the flow and the water surface line obtained by calculation through the one-dimensional model are used as boundary conditions of the local section, and the three-dimensional flow field is calculated through an analytic method on the appointed section.
In addition, the three-dimensional water flow numerical simulation method of the natural river channel also comprises the following steps: (1) the plane orthogonal network line transformation is combined with vertical dimensionless transformation, the method needs to carry out coordinate transformation on a control equation, the form is very complex, and the adaptability to the natural river channel with complex boundary conditions is poor; (2) the grid nodes can not be accurately arranged on the complex boundary of the natural river channel, and the grid needs to be encrypted to increase the accuracy of a calculation result, so that the number of grid units is huge, and the calculation cost is high; (3) the method can adapt to complex boundary conditions to a certain extent, such as grid arrangement of shallow areas, is most widely applied at present, but the control equation form after transformation is extremely complex, the calculation result needs to be converted, the calculation difficulty is increased, new errors can be introduced, the method is easy to disperse under certain conditions, and the errors are larger at complex terrain change positions.
In addition, in the process of numerical simulation of three-dimensional water flow of a natural river channel, the subdivision of three-dimensional meshes of the river channel is the most basic and important work in the numerical simulation, however, as the surface of the natural river channel is uneven, the width of the surface of the natural river channel is different, the shoreline of the natural river channel is bent, the overall shape of the river channel is extremely irregular, and the automatic division of the three-dimensional meshes by using software is very difficult or even impossible, so that the application of the three-dimensional water flow numerical simulation of the natural river channel is greatly limited.
CN201110372235.X discloses a complex river channel meshing method for river channel hydrological numerical simulation, which comprises the steps of freely dividing various complex river channel areas with tributary in and out and convergence, Jiangxin continents and the like into simple area sets, setting area control curve grid intervals according to the river channel numerical simulation requirement, generating two-dimensional grids, and merging the simple area grids to obtain an initial grid after complex river channel division. Therefore, for a specific region of a river course shoreline, the density of the dots in the region can be flexibly increased according to the requirement to realize the encryption and division of the grids in the region. In addition, the CN201810929678.6 branch-free river channel two-dimensional structure mesh subdivision method based on the topographic feature boundary line includes three steps of (1) obtaining basic data, (2) primarily subdividing a target river reach two-dimensional structure mesh, and (3) transversely encrypting a primary subdivision result. According to the method, characteristic terrain boundary lines such as a river boundary line, a body line, a beach groove boundary line and a water line are brought into a two-dimensional structure grid dividing process of a river area, so that the divided grid can be well adapted to river boundary changes.
However, the above methods can only realize two-dimensional grid subdivision of the river channel, and cannot be applied to analog computation of three-dimensional water flow of the river channel. The current three-dimensional water flow numerical simulation grid processing method of the natural river comprises the following steps: (1) the plane orthogonal network line transformation is combined with vertical dimensionless transformation, the method needs to carry out coordinate transformation on a control equation, the form is very complex, and the adaptability to the natural river channel with complex boundary conditions is poor; (2) the grid nodes can not be accurately arranged on the complex boundary of the natural river channel, and the grid needs to be encrypted to increase the accuracy of a calculation result, so that the number of grid units is huge, and the calculation cost is high; (3) the method can adapt to complex boundary conditions to a certain extent, is widely applied at present, but has the defects of extremely complex control equation form after transformation, conversion of calculation results, increase of calculation difficulty, introduction of new errors, easiness in divergence in some cases and large errors in complex places of terrain change.
Disclosure of Invention
Aiming at the defects of the prior art, the technical problems to be solved by the invention are as follows: the method for simulating the three-dimensional water flow numerical value of the natural river channel is simpler, more reliable and higher in accuracy, can better realize the subdivision of the three-dimensional space of the river channel, better realizes the three-dimensional water flow numerical simulation of the natural river channel, and improves the accuracy and stability of the three-dimensional water flow numerical simulation of the natural river channel.
In order to solve the technical problem, the invention adopts the following technical scheme:
a three-dimensional water flow numerical simulation method for a natural river channel is characterized by comprising the following steps:
firstly, adopting gridding software to carry out three-dimensional gridding subdivision on a natural river channel calculation domain in a sub-region mode;
secondly, starting FLUENT software (the FLUENT software is an existing software package related to fluid reaction, and is strong in calculation performance, good in simulation and high in calculation precision), and guiding the three-dimensional grid of the natural river channel into a three-dimensional (3D) calculation module of the FLUENT software;
and further, in the second step, after the three-dimensional grid of the natural river channel is led into a three-dimensional (3D) calculation module of FLUENT software, the grid quality is checked firstly, the accuracy of the grid is ensured to be within a preset accuracy range, no negative volume grid exists, otherwise, the first step is returned, the grid subdivision is carried out on the three-dimensional geometric model of the natural river channel again, and the grid subdivision fineness is improved. Therefore, the accuracy and reliability of subsequent calculation can be better ensured.
Selecting a solver (a solver based on pressure and a solver based on density are adopted in FLUENT software), selecting a separation solver solution based on pressure by the solver, selecting non-constant flow calculation in a time mode, and selecting a 1st-order Impplicit (first-order implicit) discrete format;
and step four, determining a calculation model, namely selecting a VOF model of the water-gas two-phase flow, and tracking a free water-gas interface by adopting a VOF method. The VOF method is an effective method for processing complex free surfaces, and can truly reflect the fluctuation condition of the water surface of a riverway. The volume fraction of aqueous phase in the control body was specified as: alpha is alpha w Controlling the body to be anhydrous and full of air as 0; alpha (alpha) ("alpha") w The control body is filled with water and has no air as 1; 0<α w <1, controlling the body to be filled with a part of water; water and airThe sum of the volume fractions of gas is 1, i.e.. alpha w +α a 1. Volume fraction of water alpha w The control differential equation of (2) is shown in the following formula, and the tracking of the water-gas interface is completed by solving the continuous equation.
In the above formula, α w Representing a volume fraction of the body of water; t represents time (unit, s); x is a radical of a fluorine atom i Representing coordinates (i ═ 1,2,3, corresponding to the x, y and z coordinates, respectively);
and then selecting a viscosity option, selecting a standard K-epsilon model (an RNG K-epsilon model or a readable K-epsilon model) as the turbulence model, wherein the two equation K-epsilon turbulence model can well reflect the influence of the water flow turbulence of the natural river channel. The influence of energy exchange in natural rivers on water flow is not obvious, so that an energy equation is not solved, and the calculation workload is reduced.
Fifthly, setting material parameters, an operation environment and boundary conditions;
further, in the fifth step, air and liquid water are selected from the material library, the air is set as a first phase, and the liquid water is set as a second phase; setting a reference pressure point position (the reference pressure point position is usually selected in the atmosphere and is consistent with the atmospheric pressure, and the pressure of other positions is conveniently calculated by taking the reference pressure point position as a standard) and a gravity acceleration (the gravity acceleration is usually a constant value, and the small difference caused by the height change is ignored so as to be convenient to calculate); then respectively defining and labeling two region areas for defining boundary conditions, using a separator tool in a Grid menu to mark the areas, and decomposing an upstream end inlet and a downstream end outlet into a submerged part (area) and an air connected part (area); boundary conditions are respectively set in the two part areas, the inlet of the submerged part is set as a mass inlet boundary, the volume fraction of water is 1, the part connected with air is set as a pressure inlet boundary, and the volume fraction of water is 0; the outlet of the submerged part is set as an outflow boundary, the part connected with the air is set as a pressure outlet, and the volume fraction of water is 0; setting the top boundary of the model as a pressure outlet boundary, wherein the water volume fraction is 0; the bottom of the model is a rough wall boundary. The setting can better accord with the actual situation, and the calculation precision is improved.
Sixthly, adjusting and setting parameters for controlling solving, selecting a Piso algorithm for pressure solving, setting an under-relaxation factor, and selecting a first-order windward discrete format;
step seven, initializing a flow field and solving;
further, in the seventh step, after initializing the flow field, a region of the initial water body is defined and marked, and then the water volume fraction of the region is assigned to 1; then setting monitoring parameters of a solving process; then, the solving time step length and the step number are set, and the solving is started. Therefore, part of the water body is filled in the calculation domain first, and the time for flowing into the water body from the inlet to fill the calculation domain can be greatly reduced.
And step eight, displaying and outputting a calculation result to obtain water flow characteristic parameters including a speed field and a pressure field. The calculation result can be output to post-processing software such as Tecplot for processing.
The method is adopted to carry out the numerical simulation calculation of the three-dimensional water flow of the river channel, so that the three-dimensional mesh division of the complex shape of the natural river channel can be realized, and enough mesh nodes are ensured to be arranged in the water depth direction; the water-gas two-phase flow VOF method can be accurately captured from the water surface; and (3) realizing the three-dimensional water flow numerical simulation of the natural river channel based on a mature FLUENT computing platform. Therefore, the invention does not need to carry out coordinate transformation on the water flow control equation, and greatly improves the accuracy and stability of the three-dimensional water flow numerical simulation of the natural river channel.
Furthermore, in the first step, the natural river integral model is firstly decomposed into continuous and non-overlapping columnar sub-domains in the horizontal direction, then each sub-domain is regularized and then is subjected to mesh subdivision by adopting meshing software, and then the subdivided sub-domains are combined to form a natural river three-dimensional mesh assembly.
The invention is based on the idea of 'discrete', and decomposes the natural river into the columnar subdomains which are continuous in the horizontal direction and do not overlap with each other, so that each subdomain is conveniently regularized with the least error cost, then the regularized subdomains can be automatically meshed by adopting software conveniently, and finally, each subdomain is merged to form the natural river three-dimensional mesh assembly. The method can conveniently and quickly realize the three-dimensional network subdivision of the complex natural river channel, and has the advantages of high efficiency, good quality of generated grids and high precision of representing the three-dimensional complex boundary characteristics of the natural river channel.
Further, the regularizing each subdomain is to convert a curved surface of a riverbed at the lower bottom surface of each subdomain into a plane.
Therefore, the mesh is converted into a regular body to facilitate subsequent mesh generation.
Further, the adopted gridding software is Gambit software.
The Gambit software is the existing software which can help analysts and designers to establish a grid-connected gridded Computational Fluid Dynamics (CFD) model, can directly realize grid subdivision on a regular three-dimensional region, and is powerful in function and fast in calculation.
Further, the first step specifically includes the steps of:
a, acquiring four boundary lines (including two boundary lines and a connecting line between corresponding end points of the two boundary lines) of a river channel in a three-dimensional water flow numerical simulation area to be calculated, constructing a horizontal plane surrounded by the four boundary lines, giving the number of nodes of each boundary line, adopting polygons capable of being spliced and extended along the horizontal plane, taking two adjacent boundary nodes as one side of the polygon, performing two-dimensional mesh subdivision on the area between the four boundary lines, dividing the area into a plurality of polygons, introducing river bed elevation, and performing interpolation to obtain the terrain elevation of each node (namely the position of a polygon corner) in each polygon unit corresponding to the position of a river bed, thereby obtaining a river bed bottom surface model formed by splicing a plurality of polygon units;
b, using each polygon unit in the river bed bottom surface model as a lower bottom surface, endowing each node of the polygon unit with certain same top elevation to form an upper top surface, obtaining a columnar three-dimensional sub-domain, and compiling node coordinates and elevations of each sub-domain into data files one by one, wherein each sub-domain is arranged in a mode of firstly arranging the lower bottom surface and then arranging the upper top surface, and the lower nodes are arranged in a reverse order;
and c, importing the node data files of all the sub-domains into Gambit software, compiling a Journal file by using a Gambit programming language, automatically generating lines, surfaces and three-dimensional polyhedrons one by one, assigning splitting node numbers to each edge of each polyhedron, automatically meshing the polyhedrons, merging coplanarity by using a face connect command after all sub-domain meshes are generated, and finally generating a natural river channel three-dimensional mesh assembly.
Therefore, the method can conveniently and quickly realize the three-dimensional mesh generation of the natural river channel to generate the natural river channel three-dimensional mesh assembly so as to meet the requirement of the natural river channel three-dimensional water flow numerical simulation, improve the accuracy, reliability and stability of the subsequent three-dimensional water flow numerical simulation, simultaneously utilize the existing simple model three-dimensional division software to realize the three-dimensional division of a complex space, and has the advantages of simple steps, strong operability, high automation degree and the like.
Further, the polygon in the step a is a triangle or a quadrangle, and the polyhedron in the step c is a pentahedron or a hexahedron.
Therefore, a triangle or a quadrangle is adopted, polygonal nodes can be conveniently arranged on the boundary, the adaptability to plane complex boundaries is good, modeling is simpler, splicing extension along the horizontal plane is conveniently realized, and two-dimensional mesh generation is conveniently realized.
Further, in the step a, four boundary lines of the natural river channel of the three-dimensional numerical value region to be calculated are obtained according to the existing river channel topographic map, and the authenticity of data of the natural river channel is guaranteed.
Further, in the step a, when the two-dimensional mesh splitting is performed, the side length range of the polygon takes values from several centimeters to several meters. Particularly, the range can be as small as possible on the basis of not influencing the processing efficiency of a computer, and the smaller the value is, the better the numerical simulation calculation precision of the three-dimensional water flow of the follow-up river channel is improved.
Further, in the step a, when the two-dimensional grid is split, the side length range of a polygon at the position of a key region of interest in the river channel is smaller, so that the distribution density of the polygon is larger. And realizing the encryption effect of the plane grid.
Therefore, the three-dimensional numerical simulation calculation precision of the river in the key region of interest can be improved, the side length of a polygon in the region of no interest can be larger, the number of three-dimensional units is reduced overall, and the calculation efficiency is improved.
Furthermore, the important region of interest in the river is a region related to the position of water conservancy facility construction or river renovation in the river.
Therefore, the three-dimensional numerical simulation calculation precision of the river channel in the engineering relevant area can be improved, and the river channel engineering construction is facilitated.
More preferably, in the step c, the nodes on the edge line in the vertical direction are distributed in a non-even manner, and the nodes are distributed more densely at the associated height position and sparsely at the non-associated height position in the subsequent calculation.
Therefore, vertical grid encryption is realized, and compared with average distribution, the calculation precision of subsequent corresponding application conditions can be better improved. For example, under the subsequent simulation calculation requirement related to the river bed bottom sediment scouring condition, the upper end is sparse, and the lower end is dense; under the requirement of simulation calculation of influence of riverbed water conditions on sailing, the upper end is dense, and the lower end is sparse; under the requirement of simulation calculation of influence of riverbed water conditions on fishes in the riverbed water conditions, the upper end and the lower end of the riverbed water conditions are sparse, and the middle of the riverbed water conditions is dense. Therefore, the vertical grid encryption condition can be flexibly adjusted according to the specific requirements of different subsequent applications. The reliability of the subsequent application calculation is greatly improved. And the method can carry out grid encryption adjustment on the horizontal plane and the vertical height direction according to the requirements. The application range of the subsequent application is greatly improved, and the precision and the reliability of the subsequent analog calculation application are improved.
And further, in the step b, assigning values to the top elevations of all nodes of the polygonal unit according to the height of the highest water level of the river channel.
Therefore, the simulation calculation of the three-dimensional numerical value of the river channel under any water level condition is ensured to be within the height range of the three-dimensional grid divided by the method, and the natural river channel three-dimensional grid assembly obtained by the method can be used for the simulation calculation of the three-dimensional numerical value of the river channel under any condition.
Further, the step c specifically comprises the following steps:
c1, inputting subdomain node coordinates and an elevation assembly data file in Gambit software;
c2 defines 6 or 8 nodes numbered d1-d6 or d1-d8 for the current sub-domain;
c3 generating 6 or 8 sides b1-b6 or b1-b8 for two-two nodes in the current subdomain;
c4 making all 6 or 8 edges in the current sub-domain generate a pentahedron or hexahedron;
c5, assigning the number of grid nodes to each edge of the current sub-domain (the number of nodes is determined according to the calculation precision, and can be a plurality of or ten nodes, and the node arrangement can be equally or unequally distributed);
c6 automatically mesh the current sub-domain;
c7 judging whether all subdomains are completed; otherwise, selecting the next adjacent subdomain and circularly executing the steps c2-c 7; if yes, go to step c 8;
c8 selecting all the surfaces, merging the coplanar surfaces by using a face connect command;
c9, completing the corresponding natural river three-dimensional mesh generation.
Thus, automatic execution of Gambit software is facilitated.
In conclusion, the method can better realize the subdivision of the three-dimensional space of the river channel, so that the three-dimensional water flow numerical simulation of the river channel can be better completed, the coordinate change of a water flow control equation is not needed, and the accuracy and the stability of the three-dimensional water flow numerical simulation of the natural river channel are improved.
Drawings
Fig. 1 is a diagram of the river situation and the riverbed topography of a research river reach of Chongqing at the upstream of the Yangtze river in the embodiment.
Fig. 2 is a three-dimensional grid section of the river reach shown in fig. 1.
Fig. 3 is a schematic water depth view of the river reach of fig. 1.
Fig. 4 is a schematic representation of the surface flow rates of the river reach of fig. 1.
Fig. 5 is a schematic diagram of the pressure field distribution of the river reach shown in fig. 1.
Fig. 6 is a schematic longitudinal profile velocity field of the river reach of fig. 1.
Fig. 7 is a schematic cross-sectional velocity field of the river reach of fig. 1.
Fig. 8 is a schematic diagram of performing two-dimensional mesh generation on an area between four boundary lines of a river channel where a three-dimensional numerical area needs to be calculated in the first step of the present invention.
FIG. 9 is a schematic representation of a single pentahedral subdomain in a first step of the present invention.
FIG. 10 is a schematic view of a single hexahedral subdomain in a first step of the present invention.
FIG. 11 is a schematic flow chart of step c in the first step of the present invention.
Fig. 12 is a schematic diagram of a natural river three-dimensional grid assembly finally generated by subdivision in the first step of the invention.
Detailed Description
The present invention will be described in further detail with reference to the following embodiments.
The specific implementation mode is as follows: in the present embodiment, the present invention will be further described with reference to examples.
As shown in figure 1, the mileage of an upstream channel of a certain river reach in the Chongqing area at the upstream of the Yangtze river is 534.5km, and the mileage of a downstream channel is 526.5km, which is about 8 km. The river reach is slightly curved, but the banks on the two sides are extremely irregular, and the Shang beach protrudes out of the center of the river from the right bank and is opposite to the group pig beach on the left bank and the Guojia mouth stone beam; the rapeseed beams are half towards the middle of the downstream inclined horizontal river, protrude about 290m in the river and are opposite to the bank door latch; the crossbeam stone beam on the left bank extends into the river obliquely downwards, the length of the crossbeam stone beam is about 250m, the head of the stone beam is higher, the elevation between the rear part of the reef and the left bank is lower, the low water period is one inland river, and the tail of the crossbeam is opposite to the dove beach rock disk in the submerged river on the south bank. The lower reaches of all reefs form a deep mass, the deep body deep pool and the shallow groove are alternated along the journey, and the deep body line is bent by the opposite of the reefs on the two sides. The river bed form enables the water flow to have obvious three-dimensional characteristics such as transverse flow, backflow, sliding beam water, bubble swirl and the like, a three-dimensional water flow mathematical model is adopted for simulation, and the working condition is calculated: upstream incoming flow rate Q30400 m 3 And s, the downstream outlet water level H is 152 m.
The method is adopted for carrying out three-dimensional water flow numerical simulation in the river reach, and specifically comprises the following steps:
1. using Gambit software, performing three-dimensional mesh generation on a natural river channel calculation domain of a researched river reach by adopting a sub-area sub-domain method, as shown in fig. 1, arranging 9235 triangular units and 4826 nodes on a plane, vertically arranging 25 nodes in water depth, and outputting a mesh file, wherein the total of 230875 pentahedral units are formed in the three-dimensional mesh.
2. And (3) starting FLUENT software, clicking a File-read command to read in a case File, importing a natural river channel three-dimensional Grid mesh File into a FLUENT 3D (three-dimensional) computing module, clicking a check command under a Grid menu to check the Grid quality, ensuring that the Grid precision is within a preset precision range and no negative volume Grid exists, and returning to the first step to re-perform Grid subdivision on a natural river channel three-dimensional geometric model and improve the Grid subdivision precision.
3. Selecting a solver: clicking Define (definition) -Model (Model) -Solver (Solver) in sequence to enter a Solver setting menu, selecting PressureBased (namely a Pressure-Based Solver) by the Solver, selecting Unsteady (namely a non-constant flow calculation option) in a Time option, selecting 1st-order Implicit (first-order implicit) discrete format in Unsteady format, and selecting default values by other items.
4. Determining a calculation model: click on Define Model Multiphase in turn, select Volume of Fluid (VOF) (Fluid Volume fraction method), set the number of phases to 2.
5. Click sequentially on Define-Model-Viscous, select the standard K-epsilon Model and the standard wall function.
6. Setting material parameters, operating environment and boundary conditions: click on Define-Model-Material in turn, selecting air and liquid water from the materials library.
7. Click sequentially on Define-Model-phase, set air to primary-phase (first phase) and water to secondary-phase (second phase).
8. Sequentially clicking the Define-Model-Operation Conditions, and setting the reference pressure position and the gravitational acceleration. The reference pressure point is selected in the atmosphere and is consistent with the atmospheric pressure, so that the pressure of the rest positions can be conveniently calculated by taking the reference pressure point as a standard; the gravity acceleration is a constant value, and small differences caused by height changes are ignored so as to facilitate calculation.
9. Clicking Adapt (definition) -region in sequence, defining and Mark two region regions for defining boundary conditions according to the upstream and downstream positions and the water level. Clicking Grid-Separate-face splits the upstream inlet and downstream outlet into flooded and air-bound parts with labeled areas, see fig. 2.
10. Sequentially clicking a Define-Model-boundary Conditions, respectively setting boundary Conditions, setting an inlet of a submerged part as a mass inlet boundary, setting a water volume fraction as 1, setting a part connected with air as a pressure inlet boundary, and setting the water volume fraction as 0; the outlet of the submerged part is set as an outflow boundary, the part connected with the air is set as a pressure outlet, and the volume fraction of water is 0; setting the top boundary of the model as a pressure outlet boundary, wherein the water volume fraction is 0; the bottom of the model is a rough wall boundary.
11. Adjusting parameters set for controlling the solution: clicking Solution, Control and Solution, selecting a Piso algorithm for pressure Solution, setting an under-relaxation factor, and selecting a first-order windward discrete format.
12. Click the Solve-initialization velocity field and the pressure field.
13. Clicking Adapt (definition) -region, defining the region according to the calculation domain range and the initial water level and marking by Mark, clicking Solve-Initialize-Patch to set the just defined and marked region as the water phase, and dividing the water volume into 1.
14. Clicking on Solve-monitors-residual sets the monitoring parameters of the solution process.
15. And clicking the solution-iteration to set a time step length and an iteration step number for solving.
16. After the calculation is finished, a File-export is clicked, the Tecplot File is selected to be output for post-processing, and water flow characteristic parameters such as a speed field and a pressure field are obtained, and the water flow characteristic parameters are shown in figures 3 to 7. (fig. 3 is a watercourse depth map, fig. 4 is a water surface flow velocity map, fig. 5 is a watercourse pressure field distribution map, fig. 6 is a watercourse longitudinal section velocity field, fig. 7 is a watercourse transverse section velocity field)
In addition, referring to fig. 8-12 when the concrete process of the first step is implemented, in the step, the natural river integral model is decomposed into continuous and non-overlapping columnar sub-domains in the horizontal direction, then each sub-domain is regularized and then is subjected to mesh division by using meshing software, and then the divided sub-domains are combined to form a natural river three-dimensional mesh assembly.
The invention is based on the idea of 'discrete', and decomposes the natural river into continuous and non-overlapping columnar sub-domains in the horizontal direction, so that each sub-domain is conveniently regularized with the least error cost, then the regularized sub-domains can be automatically meshed and subdivided by software conveniently, and finally, each sub-domain is combined to form the natural river three-dimensional mesh assembly. Therefore, the method conveniently and quickly realizes the three-dimensional network subdivision of the complex natural river channel, and has the advantages of high efficiency, good quality of generated grids and high precision of representing the three-dimensional complex boundary characteristics of the natural river channel.
Wherein, the regularizing each subdomain refers to converting the riverbed curved surface of the lower bottom surface of each subdomain into a plane.
Therefore, the mesh is converted into a regular body to facilitate subsequent mesh generation.
Wherein, the adopted gridding software is Gambit software.
The Gambit software is the existing software which can help an analyst and a designer to establish a grid-connected Computational Fluid Dynamics (CFD) model, can directly realize grid subdivision on a regular three-dimensional region, and is strong in function and quick in calculation.
When the first step is implemented, the method specifically comprises the following small steps:
a, acquiring four boundary lines (including two boundary lines and a connecting line between corresponding end points of the two boundary lines) of a river channel of a three-dimensional numerical value area to be calculated, constructing a horizontal plane surrounded by the four boundary lines, giving the number of nodes of each boundary line, adopting a polygon capable of being spliced and extended along the horizontal plane, taking two adjacent boundary nodes as one side of the polygon, performing two-dimensional mesh subdivision on the area between the four boundary lines, referring to fig. 8, subdividing the area into a plurality of polygons, introducing river bed elevation, and performing interpolation to obtain the terrain elevation of each node (namely the position of a polygon corner) in each polygon unit corresponding to a river bed position, thereby obtaining a river bed bottom model formed by splicing a plurality of polygon units;
b, using each polygon unit in the river bed bottom surface model as a lower bottom surface, endowing each node of the polygon unit with certain same top elevation to form an upper top surface, obtaining a columnar three-dimensional subdomain, and compiling the node coordinates and elevations of each subdomain into data files one by one, wherein the upper and lower nodes are arranged in a reverse order according to the mode of firstly lowering the bottom surface and then ascending the top surface;
c, importing the node data files of each sub-domain into Gambit software, compiling a Journal file by using a Gambit programming language, automatically generating lines, surfaces and three-dimensional polyhedrons one by one, assigning splitting node numbers to each edge of each polyhedron, automatically meshing the polyhedrons, merging coplanar surfaces by using a face connect command after all sub-domain meshes are generated, and finally generating a natural river three-dimensional mesh assembly.
Therefore, the method can conveniently and quickly realize the three-dimensional mesh generation of the natural river channel to generate the natural river channel three-dimensional mesh assembly so as to meet the requirements of the numerical simulation and calculation of the three-dimensional water flow of the natural river channel and improve the accuracy, reliability and stability of the subsequent three-dimensional water flow simulation calculation. Meanwhile, the method utilizes the existing simple model three-dimensional subdivision software to realize the three-dimensional subdivision of the complex space, and has the advantages of simple steps, strong operability, high automation degree and the like.
Wherein, the polygon in step a is a triangle or a quadrangle, and the polyhedron in step c is a pentahedron (as shown in fig. 9) or a hexahedron (as shown in fig. 10).
Therefore, the triangle or the quadrangle is adopted, polygonal nodes can be conveniently arranged on the boundary, the adaptability to complex boundaries is good, meanwhile, the modeling is simpler, the splicing extension along the horizontal plane is conveniently realized, and the two-dimensional mesh subdivision is conveniently realized.
In the step a, four boundary lines of the river channel of the three-dimensional numerical region to be calculated are obtained according to the existing river channel map. And the data authenticity is ensured.
And a, in the step a, when the two-dimensional grid is split, the side length range of the polygon takes values from several centimeters to several meters. Particularly, the method can be in a range as small as possible on the basis of not influencing the processing efficiency of a computer, and the smaller the value is, the more beneficial the improvement of the subsequent three-dimensional numerical simulation calculation precision of the river channel is.
In the step a, when the two-dimensional grid is split, the value of the side length range of a polygon at the position of a key region of interest in the river channel is smaller, so that the distribution density of the polygon is larger, and the grid encryption is realized.
Therefore, the three-dimensional numerical simulation calculation precision of the river channel in the key region of interest can be improved. The value of the polygon in the non-concerned area is larger, and the total number of the grid units is reduced overall, so that the operation efficiency is improved.
Wherein, the important region of interest in the river course relates to the position region for water conservancy facility construction or river course renovation in the river course.
Therefore, the three-dimensional numerical simulation calculation precision of the river channel in the engineering relevant area can be improved, and the river channel engineering construction is facilitated.
In the step c, node arrangement of the upper line in the vertical direction adopts non-average distribution, and distribution is denser in the position of the subsequent calculation associated height and distribution is sparser in the position of the non-associated height.
Therefore, vertical grid encryption is realized, and compared with average distribution, the calculation precision of subsequent corresponding application conditions can be better improved. For example, under the subsequent simulation calculation requirements related to the sediment scouring condition at the bottom of the riverbed, the upper end of the river bed is sparse, and the lower end of the river bed is dense; under the requirement of simulation calculation of influence of riverbed water conditions on sailing, the upper end is dense, and the lower end is sparse; under the requirement of simulation calculation of influence of riverbed water conditions on fishes in the riverbed water conditions, the upper end and the lower end of the riverbed water conditions are sparse, and the middle of the riverbed water conditions is dense. Therefore, the vertical grid encryption condition can be flexibly adjusted according to the specific requirements of different subsequent applications. The reliability of the subsequent application calculation is greatly improved. And the method can carry out grid encryption adjustment on the horizontal plane and the vertical height direction according to the requirements. The application range of subsequent application is greatly improved, and the precision and the reliability of subsequent analog calculation application are improved.
And b, assigning a value to the top elevation of each node of the polygonal unit according to the height of the highest water level of the river channel.
Therefore, the simulation calculation of the three-dimensional numerical value of the river channel under any water level condition is ensured to be within the height range of the three-dimensional grid divided by the method, and the natural river channel three-dimensional grid assembly obtained by the method can be used for the simulation calculation of the three-dimensional numerical value of the river channel under any condition.
Referring to fig. 11-12, the step c specifically includes the following steps:
c1, inputting subdomain node coordinates and an elevation assembly data file in Gambit software;
c2 defines 6 or 8 nodes numbered d1-d6 or d1-d8 for the current sub-domain;
c3 generating 6 or 8 sides b1-b6 or b1-b8 for two-two nodes in the current subdomain;
c4 making all 6 or 8 edges in the current sub-domain generate a pentahedron or hexahedron;
c5, assigning the number of grid nodes to each edge of the current sub-domain (the number of nodes is determined according to the calculation precision, and can be a plurality of or ten nodes, and the node arrangement can be equally or unequally distributed);
c6 automatically mesh the current sub-domain;
c7 judging whether all subdomains are completed; otherwise, selecting the next adjacent subdomain and circularly executing the steps c2-c 7; if yes, go to step c 8;
c8 selecting all the surfaces, merging the coplanar surfaces by using a face connect command;
c9, completing the corresponding natural river channel three-dimensional mesh generation, and obtaining a natural river channel three-dimensional mesh combination, as shown in figure 12.
Therefore, automatic execution of Gambit software is facilitated.
Claims (10)
1. A three-dimensional water flow numerical simulation method for a natural river channel is characterized by comprising the following steps:
firstly, adopting gridding software to carry out three-dimensional gridding subdivision on a natural river channel calculation domain in a sub-region mode;
secondly, starting FLUENT software, and guiding the three-dimensional grid of the natural river channel into a three-dimensional calculation module of the FLUENT software;
selecting a solver, selecting a pressure-based separation type solver solution by the solver, selecting non-constant flow calculation in a time mode, and selecting a 1st-order Implicit discrete format;
fourthly, determining a calculation model, selecting a VOF calculation model of water-gas two-phase flow, then selecting a viscosity option, and selecting a standard K-epsilon model, an RNG K-epsilon model or a readable K-epsilon model for the turbulence model;
fifthly, setting material parameters, an operation environment and boundary conditions;
sixthly, adjusting and setting parameters for controlling solving, selecting a Piso algorithm for pressure solving, setting an under-relaxation factor, and selecting a first-order windward discrete format;
step seven, initializing a flow field and solving;
and eighthly, displaying and outputting a calculation result to obtain water flow characteristic parameters including a speed field and a pressure field.
2. The method for simulating the three-dimensional water flow numerical value of the natural river channel according to claim 1, wherein in the second step, after the three-dimensional grid of the natural river channel is introduced into a three-dimensional computing module of FLUENT software, the grid quality is checked to ensure that the grid precision is within a preset precision range and no negative volume grid exists, otherwise, the method returns to the first step to perform grid subdivision on the three-dimensional geometric model of the natural river channel again, and the grid subdivision fineness is improved.
3. The method for numerical simulation of the three-dimensional water flow of the natural river according to claim 1, wherein in the fifth step, air and liquid water are selected from a material library, the air is set as a first phase, and the liquid water is set as a second phase; setting the position of a reference pressure point and the gravity acceleration; then respectively defining and labeling two region areas for defining boundary conditions, using a separator tool in a Grid menu to mark the areas, and decomposing an upstream end inlet and a downstream end outlet into a submerged part and an air connected part; boundary conditions are respectively set in the two part areas, the inlet of the submerged part is set as a mass inlet boundary, the volume fraction of water is 1, the part connected with air is set as a pressure inlet boundary, and the volume fraction of water is 0; the outlet of the submerged part is set as an outflow boundary, the part connected with the air is set as a pressure outlet, and the volume fraction of water is 0; setting the top boundary of the model as a pressure outlet boundary, wherein the water volume fraction is 0; the bottom of the model is a rough wall boundary.
4. The method for simulating the three-dimensional water flow numerical value of the natural river according to claim 1, wherein in the seventh step, after the flow field is initialized, a region of the initial water body is defined and marked, and then the water volume fraction of the region is assigned to 1; then setting monitoring parameters of a solving process; then, the solving time step length and the step number are set, and the solving is started.
5. The numerical simulation method of the three-dimensional water flow of the natural river channel according to claim 1, wherein in the first step, the integral model of the natural river channel is decomposed into continuous and non-overlapping columnar sub-domains in the horizontal direction, then each sub-domain is regularized and then is subjected to mesh generation by using meshing software, and then the divided sub-domains are combined to form a three-dimensional mesh assembly of the natural river channel;
wherein, the regularizing each subdomain refers to converting a riverbed curved surface of the lower bottom surface of each subdomain into a plane;
the adopted gridding software is Gambit software.
6. The method for simulating the three-dimensional water flow numerical value of the natural river according to claim 5, wherein the first step specifically comprises the following steps: a, acquiring four boundary lines of a natural river channel of an area needing to calculate three-dimensional water flow numerical values, constructing a horizontal plane surrounded by the four boundary lines, giving the number of nodes of each boundary line, adopting polygons which can be spliced and extended along the horizontal plane, taking two adjacent boundary nodes as one side of the polygon, performing two-dimensional mesh subdivision on the area between the four boundary lines to divide the area into a plurality of polygons, introducing river bed elevation, interpolating to obtain the terrain elevation of each node in each polygon unit corresponding to the position of a river bed, and further obtaining a river bed bottom model formed by splicing a plurality of polygon units;
b, using each polygon unit in the river bed bottom surface model as a lower bottom surface, endowing each node of the polygon unit with certain same top elevation to form an upper top surface, obtaining a columnar three-dimensional subdomain, and compiling the node coordinates and elevations of each subdomain into data files one by one, wherein the upper and lower nodes are arranged in a reverse order according to the mode of firstly lowering the bottom surface and then ascending the top surface;
and c, importing the node data files of all the sub-domains into Gambit software, compiling a Journal file by using a Gambit programming language, automatically generating lines, surfaces and three-dimensional polyhedrons one by one, assigning splitting node numbers to each edge of each polyhedron, automatically meshing the polyhedrons, merging coplanarity by using a face connect command after all sub-domain meshes are generated, and finally generating a natural river channel three-dimensional mesh assembly.
7. The method for numerical simulation of three-dimensional water flow of a natural river channel according to claim 6, wherein the polygon in step a is a triangle or a quadrangle, and the polyhedron in step c is a pentahedron or a hexahedron;
in the step a, when the two-dimensional grid is split, the side length range of a polygon takes values from several centimeters to several meters;
in the step a, when the two-dimensional grid is divided, the side length range of a polygon at the position of a key region of interest in the river channel is smaller, so that the distribution density of the polygon is higher;
the important concerned area in the river channel relates to a position area for water conservancy facility construction or river channel renovation in the river channel. .
8. The method for simulating the three-dimensional water flow numerical value of the natural river channel according to claim 6, wherein in the step c, the nodes on the edge line in the vertical direction are distributed in a non-even manner, and are distributed more densely at the position of the associated height in the subsequent calculation and are distributed more sparsely at the position of the non-associated height. .
9. The method for simulating the three-dimensional water flow numerical value of the natural river according to claim 6, wherein in the step b, the top elevation of each node of the polygonal unit is assigned according to the height of the highest water level of the river.
10. The method for simulating the three-dimensional water flow numerical value of the natural river according to claim 6, wherein the step c specifically comprises the following steps:
c1, inputting sub-domain node coordinates and elevation assembly data files in Gambit software;
c2 defines the 6 or 8 node numbers of the current sub-domain as d1-d6 or d1-d 8;
c3 two-by-two nodes in the current subdomain generate 6 or 8 edges b1-b6 or b1-b 8;
c4 making all 6 or 8 edges in the current sub-domain generate a pentahedron or hexahedron;
c5 specifies the number of mesh nodes for each edge of the current subdomain;
c6 automatically mesh-dividing the current sub-domain;
c7 judging whether all subdomains are completed; otherwise, selecting the adjacent next subdomain and circularly executing the steps c2-c 7; if yes, go to step c 8;
c8 selecting all the surfaces, and merging the coplanar surfaces by using a face connect command;
c9, completing the corresponding natural river three-dimensional mesh generation.
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