A method for predicting flow rate of inclined rectangular weir based on CFD

Abstract

The present invention discloses a method for predicting the flow of an inclined rectangular weir based on CFD, wherein the relative error of the selected numerical simulation method is determined through field testing of the inclined rectangular weir and numerical simulation thereof; then the target parameters are numerically calculated on a large scale through the selected numerical simulation method, and then the target parameters are corrected through the relative error of the selected numerical simulation method to obtain the field test data obtained through numerical simulation; then the calculated relationship between the water depth magnification coefficient on the effective weir of the inclined rectangular weir and the inclination angle is nonlinearly fitted to obtain an accurate expression constant coefficient; when an inclined rectangular weir with a given inclination angle and a corresponding weir height is set in a channel, the water depth upstream of the inclined rectangular weir is measured and brought into the flow expression to obtain the real-time inclined rectangular weir flow. The present invention can accurately and reasonably predict the flow of the inclined rectangular weir.

Description

Technical Field

[0001] The invention belongs to the field of fluid dynamics, and in particular relates to a method for predicting the flow of an inclined rectangular weir based on CFD. Background Art

[0002] Inclined weirs are usually used for water level regulation in the management of irrigation areas and spillways. The water flow falling from the top of the weir will form a subducting water tongue. Based on this special hydraulic phenomenon, it can be considered that the inclined weir can also be used as a flow measurement device. To this end, domestic and foreign scholars proposed a thin-walled weir flow prediction expression for ideal conditions when the inclined weir is at an inclination angle of 90° (also called a thin-walled weir) based on the orifice outflow test, assuming that the water flow is non-viscous and non-rotating. As we all know, the actual water flow is bound to be viscous and rotatory (non-ideal conditions), so the predicted thin-walled weir flow needs to be corrected by a correction coefficient. This correction coefficient is usually called the thin-walled weir flow coefficient. Subsequently, domestic and foreign scholars transformed "predicted thin-walled weir flow" into "predicted thin-walled weir flow coefficient". If the thin-walled weir flow coefficient is predicted accurately, the thin-walled weir flow prediction is accurate.

[0003] At present, there seems to be almost a consensus on the prediction of the flow coefficient of the thin-walled weir, which can be expressed by a simple linear expression. However, in the process of irrigation area or spillway management, the inclination of the inclined weir needs to be adjusted in real time according to the precise requirements of the water level or water volume of irrigation or drainage, and the thin-walled weir cannot always maintain a fixed vertical angle (90°). Through experimental observation, it is found that as the inclination of the inclined weir changes, the flow field upstream of the inclined weir changes significantly, resulting in the inclined weir flow prediction cannot follow the thin-walled weir flow change law well, which poses a higher challenge to the inclined weir flow prediction.

[0004] With the rapid development of computational fluid dynamics (CFD) and cloud computing technology, numerical simulation methods have gradually become a very effective research method due to its advantages such as convenient modeling, direct simulation of prototypes, and good experimental repeatability. However, there is no method in the prior art that uses numerical experimental methods to accurately predict the flow rate of inclined weirs. Chinese patent publication number CN106844913B discloses a method for simulating the thermodynamic characteristics of trapped air masses based on three-dimensional computational fluid dynamics (CFD). The patent uses three-dimensional computational fluid dynamics (CFD) to perform thermodynamic analysis of trapped air masses, but its method cannot be used to predict the flow rate of inclined weirs.

[0005] Therefore, how to use computational fluid dynamics (CFD) methods to accurately predict the flow of inclined weirs is a very worthy research topic. It will effectively improve the accuracy of water level regulation or water irrigation and drainage in irrigation areas or spillways, and can also lay a solid foundation for the construction of smart irrigation areas. It should be pointed out that the current forms of inclined weirs mainly include rectangles, triangles, trapezoids and semicircles. The flow characteristics of inclined weirs with different geometries may be different. Due to time and financial constraints, this technology mainly studies the flow prediction of inclined rectangular weirs. Summary of the invention

[0006] The purpose of the present invention is to overcome the shortcomings of the prior art. The present invention provides a method for predicting the flow of an inclined rectangular weir based on CFD, which can simply, accurately and reasonably predict the flow of the inclined rectangular weir, and effectively improve the accuracy of water level regulation or water irrigation and drainage in irrigation areas or spillways.

[0007] The technical solution of the present invention is a method for predicting the flow of an inclined rectangular weir based on CFD, characterized in that it comprises the following steps:

[0008] Step S1: Establish the flow expression of inclined rectangular weir according to hydraulic principles , where Q is the flow rate of the inclined rectangular weir, in m 3 / s, C is the discharge coefficient of the inclined rectangular weir; g is the acceleration of gravity, which is uniformly taken as 9.81 m / s 2 ; B is the effective weir width of the inclined rectangular weir, in m; K is the effective water depth magnification coefficient of the inclined rectangular weir; H is the effective water depth of the inclined rectangular weir, in m;

[0009] Step S2: for an inclined rectangular weir with a given inclination angle θ and a corresponding height p and length L of the inclined rectangular weir, field tests and numerical simulations are respectively performed under the same conditions to determine a relative error η during numerical simulation of the inclined rectangular weir, and the numerical simulation method used is output;

[0010] Step S3: numerically simulate several inclined rectangular weirs with different inclination angles θ and corresponding inclined rectangular weir heights p, and process the data using computational fluid dynamics post-processing software to obtain numerically simulated water depths h' on the inclined rectangular weir corresponding to different inclined rectangular weir flow rates Q under numerical simulation conditions, and then correct the relative error η during the numerical simulation of the inclined rectangular weir in step S2 to obtain the field test water depth h of the inclined rectangular weir obtained by numerical simulation, h=h'×η;

[0011] Step S4: solving the water depth magnification coefficient K on the inclined rectangular weir corresponding to different inclination angles θ in step S3;

[0012] Step S5: establishing an expression for the water depth magnification coefficient K on the inclined rectangular weir and the inclination angle θ, the expression being K=-α×θ / 90+β, where α and β are constant coefficients of the expression;

[0013] Step S6: Substitute the different inclination angles θ and the corresponding water depth magnification coefficient K on the inclined rectangular weir in step S4 into step S5 to obtain the analytical solutions α* and β* of the constant coefficients of the expression, and then the expression of the water depth magnification coefficient K on the inclined rectangular weir and the inclination angle θ is obtained as K=-α*×θ / 90+β*;

[0014] Step S7: Substitute the flow coefficient C of the inclined rectangular weir, the effective weir width B of the inclined rectangular weir and the effective water depth H of the inclined rectangular weir assigned in step S1, as well as the expressions of the water depth magnification coefficient K and the inclination angle θ of the inclined rectangular weir in step S6 into the flow expression of the inclined rectangular weir in step S1, and obtain the flow of the inclined rectangular weir as follows:

[0015] ;

[0016] By bringing in the inclination angle θ of the inclined rectangular weir, the corresponding weir height p of the inclined rectangular weir and the corresponding on-site test water depth h of the inclined rectangular weir, the real-time predicted flow Q of the inclined rectangular weir can be obtained, where b is the actual weir width of the inclined rectangular weir.

[0017] Furthermore, in step S1, the inclined rectangular weir flow is established, and the inclined rectangular weir flow expression is:

[0018] The flow coefficient C of the inclined rectangular weir is assigned a value, that is, C=0.602+0.075h / p; the effective weir width B of the inclined rectangular weir is assigned a value, that is, B=b-0.001, b is the actual weir width of the inclined rectangular weir; the effective water depth H on the inclined rectangular weir is assigned a value, that is, H=h+0.001, h is the on-site test water depth of the inclined rectangular weir.

[0019] Furthermore, the steps implemented in step S2 are specifically:

[0020] Step S21: Conducting an on-site test on the inclined rectangular weir, and before the on-site test, there is no obstacle blocking the water downstream of the inclined rectangular weir; measuring the actual width b of the inclined rectangular weir; measuring the height p of the inclined rectangular weir, that is, the vertical distance between the top of the inclined rectangular weir and the bottom of the riverbed upstream of the inclined rectangular weir; measuring the length L of the inclined rectangular weir, that is, the distance between the top of the inclined rectangular weir and the connection point between the inclined rectangular weir and the riverbed;

[0021] Calculate the inclination angle θ between the inclined rectangular weir and the riverbed, that is, arcsin(p / L), where arcsin is the inverse sine function; control the upstream water level during the field test, stop the upstream control when a cavity appears on the lower side of the water tongue at the top of the inclined rectangular weir, and after the water flow stabilizes, measure the water depth on the inclined rectangular weir at a point p that is 5 times the weir height of the inclined rectangular weir upstream of the inclined rectangular weir, that is, the field test water depth h of the inclined rectangular weir, and measure the flow rate Q of the inclined rectangular weir at the same time;

[0022] Step S22: numerically simulate the inclined rectangular weir in step S21. The height p and length L of the inclined rectangular weir in the numerical simulation are the same as those in the field test. The geometric model of the inclined rectangular weir in the numerical simulation is meshed, and the mesh is defined as a regular hexahedral mesh with a side length of γ. After the meshing is completed, the mesh calculation file is output and imported into the computational fluid dynamics software for numerical calculation. During the numerical calculation, the flow rate Q of the inclined rectangular weir is defined to be the same as the field measured flow rate in step S21. The turbulence model and numerical algorithm are arbitrarily selected. The results are exported after the calculation converges. The data is processed by the computational fluid dynamics post-processing software. The water depth h' on the numerical simulation weir corresponding to the flow rate Q of the inclined rectangular weir under the numerical simulation conditions is collected at the same position upstream of the inclined rectangular weir in step S21.

[0023] Step S23: According to the field test water depth h of the inclined rectangular weir and the water depth h' on the numerical simulation weir determined in steps S21 and S22, the relative error η=|h-h'| / h during the numerical simulation of the inclined rectangular weir is obtained, and at the same time, the side length γ of the regular hexahedral grid used in step S22, as well as the turbulence model and numerical algorithm are output.

[0024] Furthermore, when performing numerical simulation in step S3, specifically:

[0025] The geometric model of the inclined rectangular weir in the numerical simulation is the same as that in step S2; the numerical simulation method is the same as the numerical simulation method used in step S2, including the regular hexahedral grid side length γ during grid division, and the adopted turbulence model and numerical algorithm; the weir length L of the inclined rectangular weir in the numerical simulation is the same as that in step S2, and remains unchanged as the inclined rectangular weir rotates; the inclined rectangular weir is always inclined downstream along the water flow direction; the collection position of the water depth h' on the inclined rectangular weir in the numerical simulation is the same as that in step S2.

[0026] Further, in step S3: the flow rate Q of different inclined rectangular weirs under numerical simulation conditions is determined by:

[0027] First, determine the maximum and minimum values ​​of the inclined rectangular weir flow. As the inclined rectangular weir flow increases, the inclined rectangular weir flow when the top of the inclined rectangular weir just forms a subducting water tongue is defined as the minimum value of the inclined rectangular weir flow Q min, continue to increase the inclined rectangular weir flow, when the subducting water tongue just disappears at the top of the inclined rectangular weir, the inclined rectangular weir flow is defined as the maximum value of the inclined rectangular weir flow Q max ;

[0028] Then determine the calculation step length of the inclined rectangular weir flow, that is, ΔQ, and the number of numerical simulation calculations is defined as i=((Q max -Q min ) / ΔQ)+1;

[0029] Finally, the inclined rectangular weir flow is brought into the computational fluid dynamics software for numerical calculation, that is, Q1=Q min , Q2=Q min +ΔQ,Q3=Q min +2ΔQ, and so on, Q i =Q min +(i-1) ΔQ, i.e. Q max , where Q1 is the inclined rectangular weir flow rate input for the first time, Q2 is the inclined rectangular weir flow rate input for the second time, and Q3 is the inclined rectangular weir flow rate input for the third time.

[0030] Furthermore, the steps implemented in step S4 are specifically:

[0031] Step S41: Based on the flow expression of the inclined rectangular weir established in step S1 Perform a public transformation and get ;

[0032] Step S42: The flow rate Q of the inclined rectangular weir with the inclination angle θ obtained by numerical simulation in step S3 is i Corresponding on-site test water depth h i , respectively substituted into the expression of the inclined rectangular weir flow coefficient C and the expression of the effective water depth H above the inclined rectangular weir in step S1, thereby obtaining the inclined rectangular weir flow Q with an inclination angle of θ i The corresponding inclined rectangular weir discharge coefficient C i and the effective water depth H above the inclined rectangular weir i , and then the flow rate Q of the inclined rectangular weir with an inclination angle θ i , Inclined rectangular weir discharge coefficient C i , Effective water depth above the inclined rectangular weir H i The effective width of the inclined rectangular weir B = b-0.001 is brought into step S41 to obtain the flow rate Q of the inclined rectangular weir with an inclination angle of θ i The corresponding effective water depth magnification factor K above the weir i ;

[0033] Step S43: The flow rate Q of the inclined rectangular weir with an inclination angle of θ obtained in step S42 is converted to i The corresponding effective water depth magnification factor K above the weiri Taking the average value, we can get the effective water depth magnification factor K on the weir corresponding to the inclined rectangular weir with an inclination angle of θ, that is, K=∑K i / i, where i is the calculation sequence.

[0034] Further, in step S5: when performing nonlinear fitting on the expressions of the water depth magnification coefficient K on the inclined rectangular weir and the inclination angle θ, the relationship between the constant coefficients α and β always maintains the relationship of β=1+α; the unit of the inclination angle θ of the inclined rectangular weir is degree.

[0035] The beneficial effects of the present invention are as follows: the real-time flow of the inclined rectangular weir can be predicted simply, accurately and reasonably, the accuracy of water level regulation or water irrigation and drainage in the irrigation area or spillway can be effectively improved, the decision-making efficiency of urban flood control and drainage can be significantly improved, and the irrigation water guarantee rate and grain harvest of crops in the irrigation area can be effectively guaranteed. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is an elevation view of the inclined rectangular weir of the present invention;

[0037] Figure 2 It is a plan view of the inclined rectangular weir of the present invention;

[0038] Figure 3 The relationship between the flow rate of the inclined rectangular weir with L=0.15m and b=0.3m and the water depth of the inclined rectangular weir field test obtained by numerical simulation;

[0039] Figure 4 The relationship between the flow rate of the inclined rectangular weir with L=0.126m and b=1m and the water depth of the inclined rectangular weir field test obtained by numerical simulation;

[0040] Figure 5 It is a scatter plot of different inclination angles θ and the corresponding water depth magnification coefficient K on the inclined rectangular weir;

[0041] Figure 6 This paper analyzes the error between the measured and predicted values ​​of the water depth magnification factor K on the inclined rectangular weir. DETAILED DESCRIPTION

[0042] The present invention is further described below in conjunction with the accompanying drawings. A method for predicting the flow of an inclined rectangular weir based on CFD of the present invention includes first determining the accuracy of the selected numerical simulation method through field testing of the inclined rectangular weir and numerical simulation thereof, and expressing it through relative error; then numerically calculating the inclined rectangular weir on a large scale through the selected numerical simulation method (including grid generation, turbulence model and numerical method) to obtain target parameters, and then correcting the target parameters through the relative error of the selected numerical simulation method to obtain the field test data obtained through numerical simulation; then performing nonlinear fitting on the relationship between the effective weir water depth magnification factor and the inclination angle of the inclined rectangular weir to obtain an accurate expression constant coefficient; finally, predicting the real-time flow of the inclined rectangular weir under field conditions through the real-time measured water depth upstream of the inclined rectangular weir and the inclination angle of the inclined rectangular weir and the corresponding weir height.

[0043] The present invention compares field tests with corresponding computational fluid dynamics numerical calculations, calibrates the prediction accuracy of the numerical calculation method using the field test, and then uniformly corrects the numerical simulations of other field test conditions according to the prediction accuracy of the selected numerical calculation method, so that the results of the numerical calculations of other field test conditions are more scientific and effective and can meet actual flow conditions; while eliminating a large amount of numerical method verification and calibration related work, the accuracy of the computational fluid dynamics numerical simulation is improved, and the real-time flow of the inclined rectangular weir can be accurately predicted.

[0044] The method for predicting the flow of inclined rectangular weir based on CFD in this embodiment has the following specific steps:

[0045] Step S1: Establish the flow expression of inclined rectangular weir according to hydraulic principles , where Q is the flow rate of the inclined rectangular weir, in m 3 / s, C is the discharge coefficient of the inclined rectangular weir; g is the acceleration of gravity, which is uniformly taken as 9.81 m / s 2 ; B is the effective weir width of the inclined rectangular weir, in m; K is the effective water depth magnification coefficient of the inclined rectangular weir; H is the effective water depth of the inclined rectangular weir, in m;

[0046] The discharge coefficient C of the inclined rectangular weir is assigned a value, that is, C=0.602+0.075h / p; the effective weir width B of the inclined rectangular weir is assigned a value, that is, B=b-0.001, b is the actual weir width of the inclined rectangular weir; the effective water depth H on the inclined rectangular weir is assigned a value, that is, H=h+0.001, h is the on-site test water depth of the inclined rectangular weir;

[0047] Step S2: for an inclined rectangular weir with a given inclination angle θ and a corresponding height p and length L of the inclined rectangular weir, field tests and numerical simulations are respectively performed under the same conditions to determine the relative error η during numerical simulation of the inclined rectangular weir, and the numerical simulation method used is output; specifically:

[0048] Step S21: Conduct an on-site test on the inclined rectangular weir, and ensure that there are no obstacles blocking the water downstream of the inclined rectangular weir before the on-site test; measure the actual width of the inclined rectangular weir, 0.3 m; measure the height of the inclined rectangular weir, 0.106 m, that is, the vertical distance between the top of the inclined rectangular weir and the bottom of the riverbed upstream of the inclined rectangular weir; measure the length of the inclined rectangular weir, 0.15 m, that is, the distance between the top of the inclined rectangular weir and the connection point between the inclined rectangular weir and the riverbed;

[0049] The angle between the inclined rectangular weir and the riverbed is calculated to be 45°, i.e., arcsin(0.106 / 0.150)=45°. During the field test, the upstream water level is controlled. When a cavity appears on the lower side of the water tongue at the top of the weir, the upstream control is stopped. After the water flow stabilizes, the water depth on the inclined rectangular weir is measured at a height of 0.53 m, which is 5 times the height of the inclined rectangular weir upstream of the inclined rectangular weir. When the flow rate of the inclined rectangular weir is measured to be 0.015 m 3 / s, the water depth of the inclined rectangular weir in the field test was 0.0827 m; Figure 1 and Figure 2 The elevation and plan views of the inclined rectangular weir are shown respectively.

[0050] Step S22: numerical simulation is performed on the inclined rectangular weir in step S21. The height of the inclined rectangular weir in the numerical simulation is 0.106 m and the length of the inclined rectangular weir is 0.15 m, which are the same as those in the field test. The geometric model in the numerical simulation is meshed, and the mesh is defined as a regular hexahedral mesh with a side length of 10 mm. After the meshing is completed, the mesh calculation file is output and imported into the computational fluid dynamics software for numerical calculation. During the numerical calculation, the flow rate of the inclined rectangular weir is defined as 0.015 m, which is the same as the field measured flow rate in step S21. 3 / s, the turbulence model is selected as the realizable turbulence model (Realizable k-ε), the discretization method of the control equation is the finite volume method (FVM); the diffusion term adopts the second-order central difference format, the convection term adopts the fast format (QUICK), the coupling of pressure and velocity adopts the simple coupling algorithm (SIMPLEC), the calculation method adopts parallel calculation, and the numerical simulation method adopts the gas-liquid two-phase flow (VOF) method; after the calculation converges, the results are exported and the data are processed by the computational fluid dynamics post-processing software. In step S21, the flow rate of the inclined rectangular weir under the numerical simulation condition is collected at the same position upstream of the inclined rectangular weir. 0.015 m 3 / s The numerical simulation of the inclined rectangular weir corresponding to the water depth above the weir is 0.0801 m;

[0051] Step S23: According to the field test water depth of the inclined rectangular weir of 0.0827 m and the water depth on the numerical simulation weir of 0.0801 m determined in step S21 and step S22, the relative error η during numerical simulation of the inclined rectangular weir is obtained as |h-h'| / h=|0.0827-0.0801| / 0.0827=0.03;

[0052] At the same time, the hexahedral grid with a side length of 10 mm used in step S22, as well as the turbulence model and numerical algorithm are output. Specifically, the turbulence model is the realizable turbulence model (Realizable k-ε), the discretization method of the control equation is the finite volume method (FVM), the diffusion term adopts the second-order central difference format, the convection term adopts the fast format (QUICK), the coupling of pressure and velocity adopts the simple coupling algorithm (SIMPLEC), the calculation method adopts parallel computing, and the numerical simulation method adopts the gas-liquid two-phase flow (VOF) method.

[0053] Step S3: numerically simulate several inclined rectangular weirs with different inclination angles θ: 44°~90° and corresponding inclined rectangular weir heights p: 0.10~0.15 m, process the data using computational fluid dynamics post-processing software, and obtain the numerically simulated water depth h' on the inclined rectangular weir corresponding to different inclined rectangular weir flow rates Q under numerical simulation conditions, and then correct the relative error η in step S2 to obtain the field test water depth h=h'×η of the inclined rectangular weir obtained by numerical simulation;

[0054] The geometric model of the numerical simulation is the same as that in step S2; the numerical simulation method is the same as that used in step S2, including the hexahedral grid side length of 10 mm during grid generation, and the turbulence model and numerical algorithm used, specifically, the turbulence model is the realizable turbulence model (Realizable k-ε), and the discretization method of the control equation is the finite volume method (FVM); the diffusion term adopts the second-order central difference format, the convection term adopts the fast format (QUICK), the coupling of pressure and velocity adopts the simple coupling algorithm (SIMPLEC), the calculation method adopts parallel computing, and the numerical simulation method adopts the gas-liquid two-phase flow (VOF) method; the length L of the inclined rectangular weir in the numerical simulation is the same as that in step S2, and remains unchanged at 0.15 m as the inclined rectangular weir rotates; the inclined rectangular weir is always inclined downstream along the water flow direction; the collection position of the water depth h' on the inclined rectangular weir in the numerical simulation is the same as that in step S2;

[0055] The steps for determining the flow rate Q of different inclined rectangular weirs in numerical simulation are as follows: first determine the maximum and minimum flow rates of the inclined rectangular weir. As the flow rate of the inclined rectangular weir increases, the flow rate of the inclined rectangular weir when the top of the inclined rectangular weir just forms a subducting water tongue is defined as the minimum flow rate Q of the inclined rectangular weir.min , continue to increase the inclined rectangular weir flow, when the subducting water tongue just disappears at the top of the inclined rectangular weir, the inclined rectangular weir flow is defined as the maximum value of the inclined rectangular weir flow Q max ;

[0056] Then determine the calculation step length of the inclined rectangular weir flow, that is, ΔQ, and the number of numerical simulation calculations is defined as i=((Q max -Q min ) / ΔQ)+1;

[0057] Finally, the inclined rectangular weir flow is brought into the computational fluid dynamics software for numerical calculation, that is, Q1=Q min , Q2=Q min +ΔQ,Q3=Q min +2ΔQ, and so on, Q i =Q min +(i-1) ΔQ, i.e. Q max , where Q1 is the inclined rectangular weir flow rate input for the first time, Q2 is the inclined rectangular weir flow rate input for the second time, and Q3 is the inclined rectangular weir flow rate input for the third time.

[0058] Through a large number of numerical simulations, Figure 3 The relationship between the flow rate of the inclined rectangular weir with L=0.15m and b=0.3m and the water depth of the inclined rectangular weir field test obtained by numerical simulation; In order to broaden the applicability of the proposed method, steps S2 and S3 are repeated for an inclined rectangular weir with a weir length L of 0.126m and an actual width b of 1m. Figure 4 The relationship between the flow rate of the inclined rectangular weir with L=0.126m and b=1m and the water depth of the inclined rectangular weir field test obtained by numerical simulation;

[0059] Step S4: solving the water depth magnification coefficient K on the inclined rectangular weir corresponding to different inclination angles θ in step S3;

[0060] Step S41: Based on the flow expression of the inclined rectangular weir established in step S1 Perform a public transformation and get ;

[0061] Step S42: The flow rate Q of the inclined rectangular weir with the inclination angle θ obtained by numerical simulation in step S3 is i Corresponding on-site test water depth h i , respectively substituted into the expression of the inclined rectangular weir flow coefficient C and the expression of the effective water depth H above the inclined rectangular weir in step S1, thereby obtaining the inclined rectangular weir flow Q with an inclination angle of θ i The corresponding inclined rectangular weir discharge coefficient C i and the effective water depth H above the inclined rectangular weir i, and then the flow rate Q of the inclined rectangular weir with an inclination angle θ i , Inclined rectangular weir discharge coefficient C i , Effective water depth above the inclined rectangular weir H i The effective width of the inclined rectangular weir B = b-0.001 is brought into step S41 to obtain the flow rate Q of the inclined rectangular weir with an inclination angle of θ i The corresponding effective water depth magnification factor K above the weir i ;

[0062] Step S43: The flow rate Q of the inclined rectangular weir with an inclination angle of θ obtained in step S42 is converted to i The corresponding effective water depth magnification factor K above the weir i Taking the average value, we can get the effective water depth magnification factor K on the weir corresponding to the inclined rectangular weir with an inclination angle of θ, that is, K=∑K i / i, where i is the calculation sequence.

[0063] Figure 5 It is a scatter plot of different inclination angles θ and the corresponding water depth magnification coefficient K on the inclined rectangular weir;

[0064] Step S5: establishing an expression of the water depth magnification coefficient K on the inclined rectangular weir and the inclination angle θ as K=-α×θ / 90+β, where α and β are constant coefficients of the expression;

[0065] When nonlinear fitting is performed on the expressions of the water depth magnification coefficient K on the inclined rectangular weir and the inclination angle θ, the relationship between the constant coefficients α and β always maintains the relationship β=1+α; the unit of the inclination angle θ of the inclined rectangular weir is degree (°).

[0066] Step S6: Substitute the different inclination angles θ and the corresponding water depth magnification coefficients K on the inclined rectangular weir in step S4 into step S5 to obtain the analytical solutions α* and β* of the constant coefficients of the expression, and then the expression of the water depth magnification coefficient K on the inclined rectangular weir and the inclination angle θ is obtained as K=-α*×θ / 90+β*;

[0067] right Figure 5 The scatter plot of different inclination angles θ and the corresponding water depth magnification coefficient K on the inclined rectangular weir is nonlinearly fitted, and α=0.107, β=1.107 are obtained. Then, the expression of the water depth magnification coefficient K on the inclined rectangular weir and the inclination angle θ of the inclined rectangular weir with a weir length of L=0.15 m is K=-0.107×θ / 90+1.107; Figure 6 This is the error analysis between the measured and predicted values ​​of the water depth magnification factor K on the inclined rectangular weir. Figure 6 The error analysis found that the measured values ​​and predicted values ​​were very consistent, with relative errors less than 3%;

[0068] Step S7: Substitute the effective flow coefficient C of the inclined rectangular weir, the effective width B of the inclined rectangular weir, and the effective water depth H of the inclined rectangular weir assigned in step S1, as well as the expressions of the water depth magnification coefficient K and the inclination angle θ of the inclined rectangular weir in step S6 into the flow expression of the inclined rectangular weir in step S1 respectively: , the flow rate of the inclined rectangular weir is obtained as:

[0069] ;

[0070] Assume that a weir with a width b of 0.3 m, an inclination angle θ of 71.2° and a corresponding weir height p of 0.142 m is to be predicted. The field test water depth h of the inclined rectangular weir is 0.131 m. After all of these are entered, the real-time predicted flow rate of the inclined rectangular weir is 0.0294 m 3 / s.

[0071] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for predicting the flow of an inclined rectangular weir based on CFD, characterized by: The following steps are involved: Step S1: Establish the flow expression of inclined rectangular weir according to hydraulic principles , where Q is the flow rate of the inclined rectangular weir, in m 3 / s, C is the discharge coefficient of the inclined rectangular weir; g is the acceleration of gravity, which is uniformly taken as 9.81 m / s 2 ; B is the effective weir width of the inclined rectangular weir, in m; K is the effective water depth magnification coefficient of the inclined rectangular weir; H is the effective water depth of the inclined rectangular weir, in m; The discharge coefficient C of the inclined rectangular weir is assigned a value, that is, C=0.602+0.075h / p; the effective weir width B of the inclined rectangular weir is assigned a value, that is, B=b-0.001, b is the actual weir width of the inclined rectangular weir; the effective water depth H on the inclined rectangular weir is assigned a value, that is, H=h+0.001, h is the on-site test water depth of the inclined rectangular weir; Step S2: for an inclined rectangular weir with a given inclination angle θ and a corresponding height p and length L of the inclined rectangular weir, field tests and numerical simulations are respectively performed under the same conditions to determine a relative error η during numerical simulation of the inclined rectangular weir, and the numerical simulation method used is output; Step S3: numerically simulate several inclined rectangular weirs with different inclination angles θ and corresponding inclined rectangular weir heights p, and process the data using computational fluid dynamics post-processing software to obtain numerically simulated water depths h' on the inclined rectangular weir corresponding to different inclined rectangular weir flow rates Q under numerical simulation conditions, and then correct the relative error η during the numerical simulation of the inclined rectangular weir in step S2 to obtain the field test water depth h of the inclined rectangular weir obtained by numerical simulation, h=h'×η; Step S4: solving the water depth magnification coefficient K on the inclined rectangular weir corresponding to different inclination angles θ in step S3; Step S5: establishing an expression for the water depth magnification coefficient K on the inclined rectangular weir and the inclination angle θ, the expression being K=-α×θ / 90+β, where α and β are constant coefficients of the expression; Step S6: Substitute the different inclination angles θ and the corresponding water depth magnification coefficient K on the inclined rectangular weir in step S4 into step S5 to obtain the analytical solutions α* and β* of the constant coefficients of the expression, and then the expression of the water depth magnification coefficient K on the inclined rectangular weir and the inclination angle θ is obtained as K=-α*×θ / 90+β*; Step S7: Substitute the flow coefficient C of the inclined rectangular weir, the effective weir width B of the inclined rectangular weir and the effective water depth H of the inclined rectangular weir assigned in step S1, as well as the expressions of the water depth magnification coefficient K and the inclination angle θ of the inclined rectangular weir in step S6 into the flow expression of the inclined rectangular weir in step S1, and obtain the flow of the inclined rectangular weir as follows: ； By bringing in the inclination angle θ of the inclined rectangular weir, the corresponding weir height p of the inclined rectangular weir and the corresponding on-site test water depth h of the inclined rectangular weir, the real-time predicted flow Q of the inclined rectangular weir can be obtained, where b is the actual weir width of the inclined rectangular weir.

2. A method for predicting flow of inclined rectangular weir based on CFD according to claim 1, characterized in that: The steps implemented in step S2 are specifically: Step S21: Conducting an on-site test on the inclined rectangular weir, and before the on-site test, there is no obstacle blocking the water downstream of the inclined rectangular weir; measuring the actual width b of the inclined rectangular weir; measuring the height p of the inclined rectangular weir, that is, the vertical distance between the top of the inclined rectangular weir and the bottom of the riverbed upstream of the inclined rectangular weir; measuring the length L of the inclined rectangular weir, that is, the distance between the top of the inclined rectangular weir and the connection point between the inclined rectangular weir and the riverbed; Calculate the inclination angle θ between the inclined rectangular weir and the riverbed, that is, arcsin(p / L), where arcsin is the inverse sine function; control the upstream water level during the field test, stop the upstream control when a cavity appears on the lower side of the water tongue at the top of the inclined rectangular weir, and after the water flow stabilizes, measure the water depth on the inclined rectangular weir at a point p that is 5 times the weir height of the inclined rectangular weir upstream of the inclined rectangular weir, that is, the field test water depth h of the inclined rectangular weir, and measure the flow rate Q of the inclined rectangular weir at the same time; Step S22: numerically simulate the inclined rectangular weir in step S21. The height p and length L of the inclined rectangular weir in the numerical simulation are the same as those in the field test. The geometric model of the inclined rectangular weir in the numerical simulation is meshed, and the mesh is defined as a regular hexahedral mesh with a side length of γ. After the meshing is completed, the mesh calculation file is output and imported into the computational fluid dynamics software for numerical calculation. During the numerical calculation, the flow rate Q of the inclined rectangular weir is defined to be the same as the field measured flow rate in step S21. The turbulence model and numerical algorithm are arbitrarily selected. The results are exported after the calculation converges. The data is processed by the computational fluid dynamics post-processing software. The water depth h' on the numerical simulation weir corresponding to the flow rate Q of the inclined rectangular weir under the numerical simulation conditions is collected at the same position upstream of the inclined rectangular weir in step S21. Step S23: According to the field test water depth h of the inclined rectangular weir and the water depth h' on the numerical simulation weir determined in steps S21 and S22, the relative error η=|h-h'| / h during the numerical simulation of the inclined rectangular weir is obtained, and at the same time, the side length γ of the regular hexahedral grid used in step S22, as well as the turbulence model and numerical algorithm are output.

3. The method for predicting flow of inclined rectangular weir based on CFD according to claim 1, characterized in that: When performing numerical simulation in step S3, specifically: The geometric model of the inclined rectangular weir in the numerical simulation is the same as that in step S2; the numerical simulation method is the same as the numerical simulation method used in step S2, including the regular hexahedral grid side length γ during grid division, and the adopted turbulence model and numerical algorithm; the weir length L of the inclined rectangular weir in the numerical simulation is the same as that in step S2, and remains unchanged as the inclined rectangular weir rotates; the inclined rectangular weir is always inclined downstream along the water flow direction; the collection position of the water depth h' on the inclined rectangular weir in the numerical simulation is the same as that in step S2.

4. The method for predicting flow of inclined rectangular weir based on CFD according to claim 1, characterized in that: In step S3: the flow rate Q of different inclined rectangular weirs under numerical simulation conditions is determined by: First, determine the maximum and minimum values ​​of the inclined rectangular weir flow. As the inclined rectangular weir flow increases, the inclined rectangular weir flow when the top of the inclined rectangular weir just forms a subducting water tongue is defined as the minimum value of the inclined rectangular weir flow Q min , continue to increase the inclined rectangular weir flow, when the subducting water tongue just disappears at the top of the inclined rectangular weir, the inclined rectangular weir flow is defined as the maximum value of the inclined rectangular weir flow Q max ; Then determine the calculation step length of the inclined rectangular weir flow, that is, ΔQ, and the number of numerical simulation calculations is defined as i=((Q max -Q min ) / ΔQ)+1; Finally, the inclined rectangular weir flow is brought into the computational fluid dynamics software for numerical calculation, that is, Q1=Q min , Q2=Q min +ΔQ,Q3=Q min +2ΔQ, and so on, Q i =Q min +(i-1) ΔQ, i.e. Q max , where Q1 is the inclined rectangular weir flow rate input for the first time, Q2 is the inclined rectangular weir flow rate input for the second time, and Q3 is the inclined rectangular weir flow rate input for the third time.

5. The method for predicting flow of inclined rectangular weir based on CFD according to claim 1, characterized in that: The steps implemented in step S4 are specifically: Step S41: Based on the flow expression of the inclined rectangular weir established in step S1 Perform a public transformation and get ; Step S42: The flow rate Q of the inclined rectangular weir with the inclination angle θ obtained by numerical simulation in step S3 is i Corresponding on-site test water depth h i , respectively substituted into the expression of the inclined rectangular weir flow coefficient C and the expression of the effective water depth H above the inclined rectangular weir in step S1, thereby obtaining the inclined rectangular weir flow Q with an inclination angle of θ i The corresponding inclined rectangular weir discharge coefficient C i and the effective water depth H above the inclined rectangular weir i , and then the flow rate Q of the inclined rectangular weir with an inclination angle θ i , Inclined rectangular weir discharge coefficient C i , Effective water depth above the inclined rectangular weir H i The effective width of the inclined rectangular weir B = b-0.001 is brought into step S41 to obtain the flow rate Q of the inclined rectangular weir with an inclination angle of θ i The corresponding effective water depth magnification factor K above the weir i ; Step S43: The flow rate Q of the inclined rectangular weir with an inclination angle of θ obtained in step S42 is converted to i The corresponding effective water depth magnification factor K above the weir i Taking the average value, we can get the effective water depth magnification coefficient K on the weir corresponding to the inclined rectangular weir with an inclination angle of θ, that is, K=∑K i / i, where i is the calculation sequence.

6. The method for predicting flow of inclined rectangular weir based on CFD according to claim 1, characterized in that: In step S5: when performing nonlinear fitting on the expression of the water depth magnification coefficient K on the inclined rectangular weir and the inclination angle θ, the relationship between the constant coefficients α and β always maintains the relationship of β=1+α; The unit of the inclination angle θ of the inclined rectangular weir is degree.

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