CN114184239A - Channel flow measurement method based on optimal shrinkage center cylindrical rectangular groove - Google Patents
Channel flow measurement method based on optimal shrinkage center cylindrical rectangular groove Download PDFInfo
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Abstract
The invention discloses a channel flow measurement method based on an optimal shrinkage degree center cylindrical rectangular groove, which mainly comprises the steps of simulating a given center cylindrical rectangular groove under different shrinkage degree conditions through a CFD (computational fluid dynamics) method, judging whether effective water depth exists in front of the groove through the form of water jump, and obtaining the optimal shrinkage degree when the effective water depth exists in a certain minimum shrinkage degree under any flow condition; carrying out data processing on water depth and shrinkage flow-through width under different shrinkage degrees and flow conditions by means of SPSS and Origin to obtain a flow prediction formula of a central cylindrical rectangular groove based on different shrinkage degrees, bringing the optimal shrinkage degree into the flow prediction formula to obtain the flow prediction formula based on the central cylindrical rectangular groove based on the optimal shrinkage degree, placing the central cylindrical rectangular groove with the optimal shrinkage degree into a channel according to the channel size during channel flow measurement, and bringing the water depth into the flow formula after water flow is stable to obtain real-time channel flow. The invention can accurately test the channel flow, and has the advantages of convenient operation, low manufacturing cost and strong adaptability.
Description
Technical Field
The invention relates to a channel flow measurement method based on an optimal shrinkage center cylindrical rectangular groove, and belongs to the technical field of hydraulic engineering.
Background
The water management of the irrigation area is crucial to the construction of the irrigation area, and mainly refers to the reasonable adjustment and distribution of irrigation water quantity, flow and irrigation time, so that the benefits of irrigation and drainage engineering are brought into play, irrigation water sources are effectively utilized, the irrigation quality and efficiency are improved, and the stable and high yield of agriculture is promoted. The current commonly used method for water measurement in irrigation areas comprises the following steps: using water in canal system building; water is measured by using a special water measuring facility; water is measured with a current meter, etc. The method has high measurement requirement, the building cannot be damaged, deformed, leaked water, silted, blocked and the like, and internal test equipment is difficult to calibrate and maintain, and the test method is complicated and is not beneficial to application. In addition, the first task of using canal system buildings to measure water in engineering is to construct corresponding buildings, which requires a lot of manpower, material resources and financial resources. (II) the water is supplied by utilizing a special water supply setting, and the method mainly comprises four modes: firstly, a U-shaped channel flat-bottom parabola throat-section-free rectangular groove is used for measuring water quantity, the method has certain defects, the accuracy of flow prediction is poor, the scale effect is not considered during coefficient check, the flow coefficient checked on the model scale is applied to the prototype scale and is necessarily inaccurate, the speed coefficient has great experience, the application range is small, and the method can only be used for a flat-bottom channel and cannot be moved once being built; secondly, the Parshall rectangular groove is also a water measuring facility formed by contraction of open channels, and has harsh flow measuring conditions, high design and installation requirements and large measuring error; thirdly, the triangular water measuring weir has the advantages of simple structure, low manufacturing cost, convenient test and relatively high precision, but has small water passing capacity, complex calculation and poor universality; the trapezoidal measuring weir has the advantages that the structure is simple, the manufacturing cost is low, the test is convenient, when the water level in front of the weir is high, silting and congestion can be caused in a channel with poor water quality, the channel can only be used for flow measurement in clear water, the technical requirements on users during installation and use are high, and the popularization is poor; the current measuring method by using the current meter has the disadvantages of complicated current measuring process, long time consumption, poor measuring precision and difficult popularization and application in irrigation areas. With the acceleration of the modernization process, ultrasonic flow meters, electromagnetic flow meters and the like can also be applied to irrigation areas, but the ultrasonic flow meters, the electromagnetic flow meters and the like are expensive in manufacturing cost and high in maintenance cost, and the wide application of the ultrasonic flow meters, the electromagnetic flow meters and the like in the irrigation areas is limited. It becomes a difficult problem how to simply and accurately test the channel flow of the irrigation area.
Scholars at home and abroad set obstacles in the rectangular grooves to form critical flows in the rectangular grooves, wherein the critical flows comprise trihedrons, cylinders, semicylinders and the like, a flow measurement theoretical formula is provided through dimension analysis or column writing energy equations, and the flow measurement can be achieved by measuring corresponding parameters. The method for measuring the flow through the rectangular groove of the central cylinder is a simple and convenient flow measuring method with high precision, has strong applicability, and is more suitable for measuring the flow of all levels of channels in irrigation areasMore importantly, compared with obstacles such as three-surface-shaped obstacles, semi-cylinders on two sides and the like, the central cylindrical rectangular groove is simple in structure and simple in theoretical formula, but the relation coefficient of the flow and the water depth in front of the column needs to be determined in advance, and the relation between the flow and the water depth in front of the column can be obtained through dimensional analysis: q ═ a (B)c 2.5)(g0.5)(h/Bc)bAt present, students usually determine coefficients a and b through a physical model test, but the workload of the model test is large, the limiting conditions are many, errors hardly meet the precision requirement, and more importantly, when the coefficients are calibrated, the researchers usually think that the coefficients a and b obtained through 2-3 shrinkage degrees can be suitable for predicting the flow rate of a rectangular groove with any shrinkage degree, which is obviously unreasonable, and the popularization and the application of the flow measuring method of the central cylindrical rectangular groove are seriously restricted. In addition, the relation between the flow and the water depth in front of the column is usually determined by adopting a model test method at present, the calibration method has large workload, a plurality of limiting conditions and errors, the precision requirement is difficult to meet, and the influence of the shrinkage is difficult to consider in the derivation of a theoretical formula, so that the rectangular groove flow measurement method of the central cylinder is difficult to popularize and apply. In addition, the shrinkage of the rectangular groove of the central cylinder also influences the diameter of the central cylinder, which determines the amount of consumable materials of the central cylinder, and if a minimum and universal shrinkage (optimal shrinkage) is determined, the energy conservation and environmental protection are facilitated. With the rapid development of fluid dynamics (CFD) and cloud computing technologies, numerical simulation becomes another effective research means due to the advantages of convenient modeling, direct simulation of a prototype, good test repeatability and the like. However, no method for predicting the flow of the central cylindrical rectangular groove by using a numerical test means is available in the prior art. Chinese patent CN201910015788.6 discloses a method for predicting critical submergence depth of a wet room type pump station by CFD, which uses CFD to predict critical submergence depth of a pump station, but the method cannot be used to predict flow of a central cylindrical rectangular groove, and cn201811325431.x discloses a method for predicting flow of a large low-lift water pump, which uses CFD in combination with a differential pressure flow measurement method to predict flow of a large low-lift water pump, and also the method cannot be used for channel flow test of the present application. Thus, how to utilize the cloudThe flow measurement precision of the central cylindrical rectangular groove is improved by a calculation and CFD method, the influence of the shrinkage on the flow measurement precision is fully considered, and a determination method of the optimal shrinkage is provided on the basis, so that the irrigation district channel flow can be accurately and economically tested, and the method is a very worthy of research, and the construction process of realizing intelligent irrigation in the irrigation district is promoted.
Disclosure of Invention
The purpose of the invention is as follows: in order to overcome the defects in the prior art, the invention provides a channel flow measuring method based on an optimal shrinkage degree central cylindrical rectangular groove, which can predict the flow of the central cylindrical rectangular groove by using a numerical test means, can accurately and economically test the channel flow of an irrigation area under the condition of fully considering the shrinkage degree and the influence of the optimal shrinkage degree on the flow measuring precision, effectively avoids the waste of irrigation water sources, and improves the irrigation quality and efficiency.
The technical scheme is as follows: in order to solve the technical problem, the channel flow measurement method based on the optimal shrinkage degree central cylindrical rectangular groove comprises the following steps of:
step 1: establishing a physical test model of the central cylindrical rectangular groove and carrying out a physical model test, collecting the height of the submerged water depth at the front end of the cylinder after the water flow is stable, and determining the optimal shrinkage of the central cylindrical rectangular groove by a CFD (computational fluid dynamics) method;
in step 1, the determination of the optimal shrinkage r comprises the following steps:
step 1-1: carrying out a physical model test on the central cylindrical rectangular groove, manufacturing a central cylindrical rectangular groove model for fixing a certain shrinkage degree, wherein the material is transparent organic glass, the bottom of the rectangular groove is horizontally placed, the overflowing section of the rectangular groove is rectangular, the bottom width is B, the height is M, the diameter of the central cylinder is D, the ratio of the diameter of the central cylinder to the width of the rectangular groove is defined as the shrinkage degree r, and the test is carried out under different flow conditions to test the water depth in front of the central cylindrical groove;
step 1-2: determining an optimal numerical simulation method, modeling and performing numerical simulation calculation on a central cylindrical rectangular groove under a given shrinkage condition in a physical model test, meshing the established model by adopting the sizes of meshes with different scales, importing an output calculation file into Fluent, performing numerical simulation by adopting different turbulence models, dispersion methods, numerical algorithms and time step lengths, respectively deriving calculation results, performing Post-processing through CFD-Post and collecting data, finding out a calculation condition close to the test water depth of the central cylindrical rectangular groove with the given shrinkage in the step 1 from a plurality of numerical calculation data, and outputting the corresponding mesh size, turbulence models, dispersion methods, numerical algorithms and time step lengths;
step 1-3: determining the optimal shrinkage of the central cylindrical rectangular groove, keeping the width of the rectangular groove unchanged, determining the shrinkage of the central cylindrical rectangular groove by changing the diameter of the central cylinder, respectively performing geometric modeling on the central cylindrical rectangular groove under different shrinkage r conditions, and performing geometric modeling on the central cylindrical rectangular groove under different dimensionless numbers F0＝QB-1M-1.5g-0.5Under the condition, the optimal numerical simulation method obtained in the step 1-2 is adopted to carry out CFD calculation, and the dimensionless number F0The value interval is 0.01, the bottom width of the rectangular groove is kept the same during modeling, different shrinkage degrees are determined by changing the diameter of the central cylinder, the value range of the shrinkage degree r is more than 0.0 and less than 1.0, and the value interval of r is 0.01, namely 0.01, 0.02, 0.03, … …, 0.97, 0.98 and 0.99 when the geometric model is established; the order of calculation of the degree of shrinkage r is chosen as: when the calculation sequence of the shrinkage r is determined by adopting a center mean value method, namely, the flow field of the central cylindrical rectangular groove when r is 0.99 is calculated, and all dimensionless numbers F when r is 0.99 are calculated0The water jump shape of (1) is that the rectangular groove has no optimal shrinkage degree when the water jump on the column is carried out, and when r is all dimensionless numbers F of 0.990When the hydraulic jump is normal (the hydraulic jump does not occur on the column), the CFD calculation is performed by re-determining the shrinkage degree downward at a value of r ═ 0.01+0.99)/2 ═ 0.50; when r is 0.50, there is a dimensionless number F0When the hydraulic jump is on-column hydraulic jump, the upward redetermined shrinkage degree is r ═ 0.50+0.99)/2 ═ 0.745, rounded to 0.75, and when r ═ 0.50, all dimensionless numbers F0When the hydraulic jump is normal, the shrinkage is re-determined downward at a value of r ═ 0.50+0.01)/2 ═ 0.255, rounded to 0.26, and the water jump is thus characterizedCalculating the flow field of the central cylindrical rectangular groove with different shrinkage degrees until the water jump of the central cylindrical rectangular groove with a certain shrinkage degree r is a normal water jump and the water jump of the central cylindrical rectangular groove with the shrinkage degree smaller than the normal shrinkage degree by 0.01 is an on-column water jump, stopping calculating and outputting the shrinkage degree, wherein the shrinkage degree can be determined as the optimal shrinkage degree of the target rectangular groove and is recorded as r0Observing the form of the front hydraulic jump of the central cylinder in the water tank under the conditions of any shrinkage and any flow, wherein the judgment standard of the hydraulic jump form is as follows: when the hydraulic jump is on-column hydraulic jump, the shrinkage of the central cylindrical rectangular groove is ineffective shrinkage, and when the hydraulic jump is not on-column hydraulic jump (normal hydraulic jump), the shrinkage is effective shrinkage of the central cylindrical rectangular groove;
step 2: for the optimal shrinkage r which is more than or equal to the output of the step 1-30(r≥r0) 6 shrinkage degrees, namely r1, r2, r3, r4, r5 and r6 are selected, and r 1-r 6 are uniformly distributed on r0R is less than or equal to 1, the central cylindrical rectangular groove with the selected shrinkage degree is subjected to numerical calculation under different flow conditions, corresponding calculated flow Q, water depth h at the front end of the cylinder and flow width Bc after the rectangular groove is shrunk are output, and SPSS software is adopted to carry out numerical calculation on submergence water depth h at the front end of the cylinder and flow width B after the flow passage is shrunk under the conditionscAnd the corresponding calculated flow Q is combined with a theoretical formula Q ═ a (B)c 2.5)(g0.5)(h/Bc)bCarrying out nonlinear processing, respectively outputting coefficients a and b under different shrinkage r conditions, then adopting Origin to carry out fitting analysis on the coefficients a, b and r and outputting a functional relation of the coefficients, wherein g is gravity acceleration;
and step 3: substituting the fitting relational expression of the coefficients a, b and r into a theoretical formula to obtain an expression of real-time flow in the rectangular groove considering the influence of shrinkage;
and 4, step 4: will optimize the degree of shrinkage r0And corresponding contracted rectangular groove overflowing width Bc0Substituting the expression of the real-time flow in the rectangular groove considering the influence of the shrinkage in the step 3 to obtain the expression of the real-time flow in the central cylindrical rectangular groove based on the optimal shrinkage;
and 5: surveying the channel needing flow measurement in field, and measuring the channel bottom width WAmplifying the central cylindrical rectangular groove with the optimal shrinkage in the step 1 to obtain a prototype central cylindrical rectangular groove with the optimal shrinkage, wherein the amplification factor is lambda0Arranging a central cylinder rectangular groove in the channel, and measuring the depth h of the submerged water at the front end of the central cylinder after the water flow is stable0And a shrinkage width W-Wr0And (4) substituting the expression based on the real-time flow in the central cylindrical rectangular groove with the optimal shrinkage obtained in the step (4) to obtain the real-time channel flow.
Further, in the step 1-1, the length L of the rectangular groove is not less than 10D, and the length L of the central cylinder from the overflow section to the inlet section is the diameter perpendicular to the positive direction of the incoming flowinNot less than 7D, length L from outlet sectionoutNot less than 3D, wherein D is central cylinder diameter, and central cylinder overlaps with rectangular channel central symmetry face along the cross section that rivers positive direction diameter place.
Further, in the step 1-1, model tests are performed on the central cylindrical rectangular groove under different flow conditions, the flow value is selected from small to large, the water depth in the rectangular groove is gradually deepened along with the increase of the flow, the test is stopped when the water depth at the inlet of the rectangular groove is lower than the height of the rectangular groove by 0.2D, D is the diameter of the cylinder, the flow Qt in the rectangular groove is tested through an electromagnetic flowmeter in the test process, the submergence depth ht at the front end of the corresponding central cylinder is read through a water ruler arranged at the front end of the cylinder, subscript t of Qt and ht represents the test conditions, the unit of Q is L/s, and the unit of h is cm.
Further, hexahedral structured grids of different scales are adopted in grid division in the step 1-2, an external expansion structure is adopted in central cylindrical grid division, so that a plurality of different grid schemes are obtained, a VOF method is adopted in Fluent calculation for each grid scheme, different turbulence models and different numerical algorithms are selected for the VOF method, flow adopted in numerical calculation corresponds to output flow tested in the step 1 one to one, boundary conditions adopted in calculation are that an inlet is a speed inlet, an outlet is a pressure outlet, a surface is a pressure inlet, a solid boundary is set to wall, an initial condition is that air proportion is 100%, water depth hs obtained through numerical simulation is water depth hs under the condition that water and air in Post-processing CFD-Post respectively occupy 50% of free liquid level, the unit is cm, and subscript s is a digital-analog condition.
Further, error analysis is carried out on the water depth ht under the test condition obtained in the step 1-2 and the water depth hs under the digital-analog condition, the calculation formula is that | ht-hs | and/ht are less than or equal to k%, wherein | | | represents an absolute value, and when all the k values under a certain numerical calculation scheme are not more than 7, a grid division scheme and a Fluent setting scheme are output.
Further, in step 3, the relationship between the coefficient a and r is expressed by a quadratic term a ═ a1r2+B1r+C1The relation between the coefficient b and r is expressed in the form of a quadratic term b ═ a2r2+B2r+C2Wherein A is1，A2，B1，B2，C1，C2Are column term coefficients.
Further, in the step 4, based on the expression of real-time flow in the central cylindrical rectangular slot with the optimal degree of contraction
r0And Bc0The flow width of the rectangular groove corresponding to the optimal shrinkage degree and the optimal shrinkage degree is obtained.
Further, in the step 5, the real-time channel flow obtained based on the expression of the real-time flow in the central cylindrical rectangular groove with the optimal contraction degree is
Furthermore, cloud computing technology is introduced into both the model and prototype CFD computing in the invention, so that the numerical computing precision and the computing efficiency can be effectively improved.
The invention tests the real-time flow in irrigation district channels by a channel flow measuring method based on a central cylindrical rectangular groove with optimal shrinkage, which comprises the steps of verifying a numerical simulation method, carrying out numerical calculation and physical tests on a rectangular groove model, and analyzing and comparing the submergence depth at the front end of the cylinder to obtain a reasonable CFD numerical scheme comprising a mesh subdivision mode, a turbulence model and a numerical algorithm; then simulating a plurality of shrinkage degrees (fixing the width of the water tank and changing the diameter of the central cylinder) by obtaining a CFD numerical scheme, judging the pre-column water depth when the water jump on the column occurs in the central cylindrical rectangular groove as an invalid water depth, judging the pre-column water depth when the water jump on the column does not occur in the central cylindrical rectangular groove as an effective water depth, and outputting the minimum shrinkage degree when the effective water depth exists under all flow working conditions as the optimal shrinkage degree; then, the SPSS carries out nonlinear analysis on the water depth at the front end of the cylinder, the width of the corresponding rectangular groove after contraction and the calculated flow under the condition of different degrees of contraction which are output and are more than or equal to the optimal degree of contraction, and is combined with a theoretical formula to obtain a relational expression of a variable coefficient and the degree of contraction in the theoretical formula, and then the variable coefficient expressed by the degree of contraction is brought back to the theoretical formula to obtain a flow prediction formula of the rectangular groove with the center cylinder under the condition of any degree of contraction which is more than or equal to the optimal degree of contraction; and finally, substituting the obtained optimal shrinkage and the shrinkage width corresponding to the optimal shrinkage into a flow prediction formula under any shrinkage condition with the optimal shrinkage being more than or equal to the optimal shrinkage to obtain an expression based on the flow of the central cylindrical rectangular groove with the optimal shrinkage. According to the invention, the accuracy of CFD numerical simulation is improved by comparing a physical model test with a corresponding model CFD numerical calculation and using the model test to constrain a numerical calculation method, prototype data are predicted by calculating a prototype rectangular groove by an obtained high-precision numerical method, the influence of the shrinkage on the precision of a prediction result is considered, and how to reduce the manufacturing cost of a central cylinder to the minimum is further considered, so that the optimal shrinkage of any central cylinder rectangular groove is provided, and finally the real-time flow of a channel under the condition of the optimal shrinkage in an irrigation area can be accurately predicted.
Has the advantages that: the channel flow measurement method based on the central cylindrical rectangular groove with the optimal contraction degree can simply, accurately and economically predict the real-time flow of the channel in the irrigation area, so that the utilization efficiency of irrigation water is improved, the phenomenon that return water is wasted due to overlarge flow or irrigation is insufficient due to undersize flow is avoided, the optimal contraction degree of the central cylindrical rectangular groove is provided, the manufacturing consumables of the central cylinder are effectively reduced, and the manufacturing cost is saved.
Drawings
FIG. 1 is a flow chart of a channel flow measurement method based on an optimal shrinkage degree central cylindrical rectangular groove;
FIG. 2 is a schematic diagram of a central cylindrical rectangular slot model;
FIG. 3 is a split view of a central cylindrical rectangular slot grid;
FIG. 4 is a diagram of verification of numerical simulation accuracy of a central cylindrical rectangular groove;
FIG. 5 is a diagram of a central cylindrical rectangular channel numerically simulated free liquid level;
FIG. 6 is a schematic view of a normal hydraulic jump of a central cylindrical rectangular tank;
FIG. 7 is a schematic view of a hydraulic jump on a central cylindrical rectangular groove column;
FIG. 8 is a diagram illustrating the calculation of the optimal shrinkage;
FIG. 9 is a drawing showing data acquisition of the depth of water submerged at the front end of a cylinder in a central cylindrical rectangular groove with various degrees of contraction;
FIG. 10 is a graph of a quadratic polynomial fit of r to coefficient a;
FIG. 11 is a graph of a quadratic polynomial fit of r to coefficient b.
Detailed Description
The present invention will be further described with reference to the accompanying drawings.
A flow chart of the channel flow measurement method based on the optimal shrinkage degree central cylindrical rectangular groove in this embodiment is shown in fig. 1, and the specific steps are as follows:
step 1: establishing a physical test model of the central cylindrical rectangular groove and carrying out a physical model test, collecting the height of the submerged water depth at the front end of the cylinder after the water flow is stable, and determining the optimal shrinkage of the central cylindrical rectangular groove by a CFD (computational fluid dynamics) method;
in the physical model in the step 1-1, the central cylindrical rectangular groove model is made of transparent organic glass, the bottom of the rectangular groove is horizontally placed, the flow cross section of the rectangular groove is rectangular, the bottom width is 17cm, the height is 30cm, the diameter of the central cylinder is 11.4cm, and the corresponding shrinkage ratio is 0.670.
The length of the rectangular groove is 300cm, the length of the overflow section where the diameter of the central cylinder perpendicular to the positive direction of the incoming flow is located from the inlet section is 200cm, the length of the overflow section from the outlet section is 100cm, and the section where the diameter of the central cylinder along the positive direction of the incoming flow is located is overlapped with the central symmetry plane of the rectangular groove.
In the test process, the flow rates are 7.026L/s, 8.080L/s, 9.016L/s, 10.070L/s, 11.241L/s, 11.475L/s, 12.178L/s, 14.520L/s, 20.258L/s and 22.482L/s from small to large respectively. When the shrinkage degree is measured by test, the water depth is 15.785cm, 16.861cm, 17.523cm, 18.441cm, 18.578cm, 19.254cm, 19.844cm, 20.920cm, 25.020cm, 25.439cm and 26.961 cm.
Step 1-2: carrying out numerical simulation calculation on a central cylindrical rectangular groove of a physical model test, establishing a geometric model of the central cylindrical rectangular groove as shown in figure 2, dividing grids as shown in figure 3, outputting a calculation file, importing Fluent to carry out numerical calculation, exporting a calculation result, carrying out Post-processing through CFD-Post, and collecting data;
the method adopts a VOF method in Fluent calculation, adopts boundary conditions that an inlet is a speed inlet, an outlet is a pressure outlet, a surface is a pressure inlet, a solid boundary is set to be wall, and the initial condition is that the air proportion is 100 percent;
the numerical simulation flow rate and the model test flow rate are same and respectively 7.026L/s, 8.080L/s, 9.016L/s, 10.070L/s, 11.241L/s, 11.475L/s, 12.178L/s, 14.520L/s, 20.258L/s and 22.482L/s;
finding out a calculation working condition close to the water depth tested in the step 1-1 from a plurality of numerical calculation results, and outputting a corresponding grid size, a turbulence model and a numerical algorithm;
when the water depth and height obtained by numerical simulation are the water depth under the condition that water and air respectively account for 50% of free liquid level in the Post-treatment CFD-Post, and the water depth obtained by simulation is 14.873cm, 15.893cm, 17.145cm, 18.417cm, 19.244cm, 19.702cm, 20.143cm, 21.275cm, 25.607cm, 26.098cm and 27.678cm, the relative error between the water depth obtained by numerical simulation and the water depth obtained by model test is not more than 7% (as shown in figure 4), the grid subdivision at the moment is output, the grid is 1cm multiplied by 1cm, the turbulence model is Realicablk-epsilon, and the discrete mode of the control equation is finite volume method FVM; the diffusion term adopts a second-order central difference format, the convection term adopts a Quick format, the coupling of pressure and speed adopts a SIMPLEC algorithm, and the calculation mode adopts parallel calculation.
And a specific numerical calculation step:
1. modeling a central cylindrical rectangular groove of the model by using three-dimensional modeling software SolidWorks (as shown in FIG. 2), and then outputting a suffix IGS file;
2. importing the suffix name IGS file into mesh subdivision software Ansys ICEM, carrying out mesh subdivision on a central cylindrical rectangular groove shown in figure 2 (shown in figure 3), wherein the mesh size is 1cm multiplied by 1cm, the mesh type is hexahedron structured mesh, and then generating an Ansys Fluent numerical value to calculate the suffix name of the file;
3. importing the calculation file into an Ansys Fluent to calculate, wherein the specific setting mode is as follows:
reducing x, y and z of Scale in General by 0.001 times in a same ratio, and enabling the modeling and the numerical calculation to be consistent in geometric dimension;
opening multiphase flow Volume of Fluid setting in Models, selecting Implicit calculation Implicit, and taking 1 × 10 for Curian number-8Considering the volume Force Implicit Body Force, selecting Realizblek-epsilon by a turbulence model;
adding a medium water into Matricals, wherein the main term in the multiphase flow is the water, and the secondary term in the multiphase flow is air;
selecting an inlet as a speed inlet from Boundary Conditions, adopting a side wall condition for wall, adopting an outlet as a pressure outlet, and adopting a pressure inlet on the upper surface;
coupling of pressure and speed in Solution Methods adopts a Coupled algorithm, and the discrete mode of a control equation is FVM; the diffusion item adopts a second-order central difference format, and the convection item adopts a Quick format;
the Moinors sets the convergence condition of the calculation, and in the calculation, in order to improve the calculation precision, the consistency, x, y and z are all set to reach 1 multiplied by 10-6Stopping the calculation;
setting an Initialization method as Standard Initialization in Solution Initialization, and setting 100% of an initial item as air;
setting Time Step Size to be 0.01s, number Time Steps to be 200000, Max operations to be 20, automatically saving Step Size to be 100 and 1s and saving a Calculation result in Run Calculation;
storing the Fluent calculation result after the calculation is stopped, and importing CFD-Post processing, wherein the method comprises the following specific steps:
the Isosurface is set, the water volume Fraction is set to be 50%, the free liquid level (as shown in figure 5) can be obtained, and the water depth at the front end of the cylinder can be measured.
Step 1-3: determining the optimal shrinkage of the central cylindrical rectangular groove, keeping the width of the rectangular groove unchanged, determining the shrinkage of the central cylindrical rectangular groove by changing the diameter of the central cylinder, respectively performing geometric modeling on the central cylindrical rectangular groove under different shrinkage r conditions, and performing geometric modeling on the central cylindrical rectangular groove under different dimensionless numbers F0＝QB-1M-1.5g-0.5Carrying out CFD calculation by adopting the optimal numerical simulation method obtained in the step 1-2 under the condition, keeping the bottom width of the rectangular groove the same during modeling, determining different shrinkage degrees by changing the diameter of the central cylinder, wherein the value range of the shrinkage degree r is more than 0.0 and less than 1.0, and the value interval of r is 0.01, namely 0.01, 0.02, 0.03, … …, 0.97, 0.98 and 0.99 during establishing the geometric model; the order of calculation of the degree of shrinkage r is chosen as: when the calculation sequence of the shrinkage r is determined by adopting a center mean value method, namely, the flow field of the central cylindrical rectangular groove when r is 0.99 is calculated, and all dimensionless numbers F of r is 0.99 are calculated0The hydraulic jump (c) of (a) is a normal hydraulic jump (as shown in fig. 6), and CFD calculation is performed with the degree of contraction re-determined downward as r ═ 0.01+0.99)/2 ═ 0.50, and r ═ 0.50 for all dimensionless numbers F0The water jump form (2) is normal water jump, the shrinkage is re-determined downwards as r ═ 0.50+0.01)/2 ═ 0.255, the value of r ═ 0.26 is rounded off, and CFD calculation is carried out, when the dimensionless number F is0When the water jump is less than 0.173, the water jump is on-column water jump (as shown in fig. 7), CFD calculation is carried out when the upward redetermined shrinkage degree value is r ═ 0.26+0.50)/2 ═ 0.38, the water jump is normal water jump, CFD calculation is carried out when the downward redetermined shrinkage degree value is r ═ 0.38+0.26)/2 ═ 0.32, and when the dimensionless number F is smaller than0The water jump state is water jump on column when < 0.122, the upward redetermined shrinkage degree is r ═ 0.32+0.38)/2 ═ 0.35, and all dimensionless numbers F thereof are0Water jumpFor normal hydraulic jump, the downward redetermined shrinkage has a value of r ═ 0.35+0.32)/2 ═ 0.34, when the dimensionless number F is0If the water jump is on-column water jump < 0.106 and the calculation results of all the above shrinkage degrees are shown in FIG. 8, the optimal shrinkage degree of the central cylindrical rectangular groove is r0＝0.35。
Step 2: respectively carrying out geometric modeling on the rectangular groove with the center cylinder in the step 1-1 under the condition of different shrinkage degrees, carrying out CFD calculation on the split grid after the modeling is finished, carrying out Post-processing on the calculation result by adopting CFD-Post (the result is shown in figure 9), wherein the grid splitting mode, the Fluent setting method and the CFD-Post-processing method are the same as the numerical method output in the step 1-2, SPSS software is adopted to carry out submerged water depth at the front end of the output cylinder, the overflow width after the runner is shrunk and the corresponding calculated flow, and the result theoretical formula Q is a (B)c 2.5)(g0.5)(h/Bc)bAnd performing nonlinear processing, respectively outputting coefficients a and b under different gradient conditions, performing fitting analysis on the coefficients a, b and r by adopting Origin, and outputting a functional relationship of the coefficients, wherein the expression form of the relationship between the coefficients a and r is shown in figure 10 by quadratic fitting, and the expression form of the relationship between the coefficients b and r is shown in figure 11 by quadratic fitting.
And step 3: substituting the fitting relation of the coefficients a, B and r into a theoretical formula Q ═ a (B)c 2.5)(g0.5)(h/Bc)bThe expression of the real-time flow of the rectangular groove can be obtained as
And 4, step 4: substituting the optimal contraction degree of 0.35 into the step 3 to obtain an expression Q which is 0.606 (B) based on the real-time flow in the central cylindrical rectangular groove of the optimal contraction degreec 2.5)(g0.5)(h/Bc)1.571
And 5: measuring the bottom width of a channel in an irrigation area to be 1.7m, amplifying the bottom width of the channel by 10 times compared with the bottom width of the rectangular groove of the test model in the step 1, wherein the shrinkage r is the optimal shrinkage of 0.35, adaptively arranging the rectangular groove of the prototype center cylinder with the amplification of 10 times and the shrinkage of 0.35 in the channel, and measuring the right center cylinder after the water flow is stableThe front end submerged depth is 0.5m, the corresponding contracted rectangular groove overflowing width is 1.7 x (1-0.35) ═ 1.105m, and the real-time channel flow is 0.701m by substituting the parameters into a real-time flow expression3/s。
The above description is only of the preferred embodiments of the present invention, and it should be noted that: it will be apparent to those skilled in the art that various modifications and adaptations can be made without departing from the principles of the invention and these are intended to be within the scope of the invention.
Claims (8)
1. A channel flow measurement method based on an optimal shrinkage center cylindrical rectangular groove is characterized by comprising the following steps:
step 1: establishing a physical test model of the central cylindrical rectangular groove and carrying out a physical model test, collecting the height of the submerged water depth at the front end of the cylinder after the water flow is stable, and determining the optimal shrinkage of the central cylindrical rectangular groove by a CFD (computational fluid dynamics) method;
in step 1, the determination of the optimal shrinkage r includes the following steps:
step 1-1: carrying out a physical model test on the central cylindrical rectangular groove, manufacturing a central cylindrical rectangular groove model with a certain fixed shrinkage degree, wherein the material is transparent organic glass, the bottom of the rectangular groove is horizontally placed, the overflowing section of the rectangular groove is rectangular, the bottom width is B, the height is M, the diameter of the central cylinder is D, the ratio of the diameter of the central cylinder to the width of the rectangular groove is defined as the shrinkage degree r, carrying out the test under the condition of different flow Q, and testing the water depth in front of the central cylindrical cylinder;
step 1-2: determining an optimal numerical simulation method, modeling and performing numerical simulation calculation on a central cylindrical rectangular groove under a given shrinkage condition in a physical model test, meshing the established model by adopting the sizes of meshes with different scales, importing an output calculation file into Fluent, performing numerical simulation by adopting different turbulence models, dispersion methods, numerical algorithms and time step lengths, respectively deriving calculation results, performing Post-processing through CFD-Post and collecting data, finding out a calculation condition close to the test water depth of the central cylindrical rectangular groove with the given shrinkage in the step 1 from a plurality of numerical calculation data, and outputting the corresponding mesh size, turbulence models, dispersion methods, numerical algorithms and time step lengths;
step 1-3: determining the optimal shrinkage of the central cylindrical rectangular groove, keeping the width of the rectangular groove unchanged, determining the shrinkage of the central cylindrical rectangular groove by changing the diameter of the central cylinder, respectively performing geometric modeling on the central cylindrical rectangular groove under different shrinkage r conditions, and performing geometric modeling on the central cylindrical rectangular groove under different dimensionless numbers F0＝QB-1M-1.5g-0.5Under the condition, the optimal numerical simulation method obtained in the step 1-2 is adopted to carry out CFD calculation, wherein the bottom width is B, the height is M, g is the gravity acceleration, and Q is the flow given by the central cylindrical rectangular groove during simulation; dimensionless number F0The value interval is 0.01, the bottom width of the rectangular groove is kept the same during modeling, different shrinkage degrees are determined by changing the diameter of the central cylinder, the value range of the shrinkage degree r is more than 0.0 and less than 1.0, and the value interval of r is 0.01, namely 0.01, 0.02, 0.03, … …, 0.97, 0.98 and 0.99 when the geometric model is established; the order of calculation of the degree of shrinkage r is chosen as: when the calculation sequence of the shrinkage r is determined by adopting a center mean value method, namely, the flow field of the central cylindrical rectangular groove when r is 0.99 is calculated, and all dimensionless numbers F when r is 0.99 are calculated0The water jump shape of (1) is that the rectangular groove has no optimal shrinkage degree when the water jump on the column is carried out, and when r is all dimensionless numbers F of 0.990When the hydraulic jump is normal, the shrinkage is re-determined downwards to be r ═ 0.01+0.99)/2 ═ 0.50, and CFD calculation is carried out; when r is 0.50, there is a dimensionless number F0When the hydraulic jump is on-column hydraulic jump, the upward redetermined shrinkage degree is r ═ 0.50+0.99)/2 ═ 0.745, rounded to 0.75, and when r ═ 0.50, all dimensionless numbers F0When the hydraulic jump is normal, the value of the contraction degree is re-determined downwards as r ═ 0.50+0.01)/2 ═ 0.255, rounded to 0.26, and the flow field of the central cylindrical rectangular groove with different contraction degrees is calculated by analogy until the hydraulic jump of the central cylindrical rectangular groove with a certain contraction degree r is normal, and when the hydraulic jump of the central cylindrical rectangular groove with the contraction degree smaller than 0.01 is on-column hydraulic jump, the calculation is stopped and the contraction degree is output, and the contraction degree can be determined as the optimal contraction degree of the target rectangular grooveDegree is recorded as r0Observing the form of the front hydraulic jump of the central cylinder in the water tank under the conditions of any shrinkage and any flow, wherein the judgment standard of the hydraulic jump form is as follows: when the hydraulic jump is on-column hydraulic jump, the shrinkage of the central cylindrical rectangular groove is ineffective shrinkage, and when the hydraulic jump is not on-column hydraulic jump, the shrinkage is effective shrinkage of the central cylindrical rectangular groove;
step 2: for the optimal shrinkage r which is more than or equal to the output of the step 1-30I.e. r is ≧ r0Selecting 6 shrinkage degrees, namely r1, r2, r3, r4, r5 and r6, wherein r 1-r 6 are uniformly distributed in r0R is less than or equal to 1, the central cylindrical rectangular groove with the selected shrinkage degree is subjected to numerical calculation under different flow conditions, corresponding calculated flow Q, water depth h at the front end of the cylinder and flow width Bc after the rectangular groove is shrunk are output, and SPSS software is adopted to carry out numerical calculation on submergence water depth h at the front end of the cylinder and flow width B after the flow passage is shrunk under the conditionscAnd corresponding calculated flow rate Q, in combination with the theoretical formula Q ═ a (B)c 2.5)(g0.5)(h/Bc)bCarrying out nonlinear processing, respectively outputting coefficients a and b under different shrinkage r conditions, then adopting Origin to carry out fitting analysis on the coefficients a, b and r and outputting a functional relation of the coefficients, wherein g is gravity acceleration;
and step 3: substituting the fitting relational expression of the coefficients a, b and r into a theoretical formula to obtain an expression of real-time flow in the rectangular groove considering the influence of shrinkage;
and 4, step 4: will optimize the degree of shrinkage r0And corresponding contracted rectangular groove overflowing width Bc0Substituting the expression of the real-time flow in the rectangular groove considering the influence of the shrinkage in the step 3 to obtain the expression of the real-time flow in the central cylindrical rectangular groove based on the optimal shrinkage;
and 5: surveying the channel needing flow measurement on the spot, measuring the channel bottom width W, amplifying the central cylindrical rectangular groove with the optimal shrinkage in the step 1 to obtain the central cylindrical rectangular groove with the prototype optimal shrinkage, wherein the amplification factor is lambda0Arranging a central cylinder rectangular groove in the channel, and measuring the depth h of the submerged water at the front end of the central cylinder after the water flow is stable0And a shrinkage width W-Wr0Carry over to step 4And obtaining the real-time channel flow based on the expression of the real-time flow in the central cylindrical rectangular groove with the optimal shrinkage.
2. The channel flow measurement method based on the central cylindrical rectangular groove with the optimal degree of contraction as claimed in claim 1, wherein: in the step 1-1, the length L of the rectangular groove is not less than 10D, and the length L of the central cylinder from the overflow section to the inlet section is the diameter perpendicular to the positive direction of the incoming flowinNot less than 7D, length L from outlet sectionoutNot less than 3D, wherein D is central cylinder diameter, and central cylinder overlaps with rectangular channel central symmetry face along the cross section that rivers positive direction diameter place.
3. The channel flow measurement method based on the central cylindrical rectangular groove with the optimal degree of contraction as claimed in claim 1, wherein: in the step 1-1, model tests are carried out on the central cylindrical rectangular groove under different flow conditions, the flow value is selected from small to large, the water depth in the rectangular groove is gradually deepened along with the increase of the flow, the test is stopped when the water depth at the inlet of the rectangular groove is lower than 0.2D of the height of the rectangular groove, D is the diameter of the cylinder, the flow Qt in the rectangular groove is tested through the electromagnetic flowmeter in the test process, the submerging water depth ht at the front end of the corresponding central cylinder is read through the installation of a water gauge at the front end of the cylinder, subscript t of the Qt and the subscript t of the ht represent the test conditions, the unit of the Qt is L/s, and the unit of the ht is cm.
4. The channel flow measurement method based on the central cylindrical rectangular groove with the optimal degree of contraction as claimed in claim 1, wherein: in the step 1-2, hexahedral structured grids with different scales are adopted in grid division, an external expansion structure is adopted in central cylindrical grid division, so that a plurality of different grid schemes are obtained, a VOF method is adopted in Fluent calculation for each grid scheme, different turbulence models and different numerical algorithms are selected for the VOF method, flow adopted in numerical calculation corresponds to output flow tested in the step 1 one by one, boundary conditions adopted in calculation are that an inlet is a speed inlet, an outlet is a pressure outlet, a surface is a pressure inlet and a solid boundary is set to wall, the initial condition is that air proportion is 100%, the water depth obtained in numerical simulation is water depth hs obtained by Post-processing CFD-Post under the condition that water and air respectively occupy 50% of free liquid level, the unit is cm, and subscript s is a digital-analog condition.
5. The channel flow measurement method based on the central cylindrical rectangular groove with the optimal degree of contraction as claimed in claim 1, wherein: and (3) carrying out error analysis on the water depth ht under the test condition obtained in the step (1-2) and the water depth hs under the digital-analog condition, wherein the calculation formula is that | ht-hs | and/ht are less than or equal to k%, in the formula, | | represents an absolute value, and when all the k values under a certain numerical calculation scheme are not more than 7, a grid division scheme and a Fluent setting scheme are output.
6. The canal flow measurement method based on the central cylindrical rectangular groove with the optimal degree of contraction as claimed in claim 1, wherein in the step 3, the relation between the coefficient a and the coefficient r is expressed in the form of a quadratic term a ═ a1r2+B1r+C1The relation between the coefficient b and r is expressed in the form of a quadratic term b ═ a2r2+B2r+C2Wherein A is1，A2，B1，B2，C1，C2Are column term coefficients.
7. The channel flow measurement method based on the central cylindrical rectangular groove with optimal degree of contraction as claimed in claim 6, wherein in step 4, the expression of real-time flow in the central cylindrical rectangular groove based on optimal degree of contraction
r0And Bc0The flow width of the rectangular groove corresponding to the optimal shrinkage degree and the optimal shrinkage degree is obtained.
8. The channel flow measurement method based on the central cylindrical rectangular groove with the optimal degree of contraction as claimed in claim 6, wherein in the step 5, the real-time flow in the central cylindrical rectangular groove based on the optimal degree of contraction is measuredThe real-time channel flow obtained by the expression of the quantity is as follows:
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN116384289A (en) * | 2023-06-05 | 2023-07-04 | 江西省水利科学院(江西省大坝安全管理中心、江西省水资源管理中心) | Method for predicting pier block type fishway flow through computational fluid dynamics |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN116384289A (en) * | 2023-06-05 | 2023-07-04 | 江西省水利科学院(江西省大坝安全管理中心、江西省水资源管理中心) | Method for predicting pier block type fishway flow through computational fluid dynamics |
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