CFD-DEM-based numerical simulation method and system for two-phase flow of water pump

Abstract

The application discloses a water pump two-phase flow numerical simulation method and system based on CFD-DEM, and belongs to the sewage pump design field.The process of the application is as follows: a CFD method is used to calculate the internal flow field of the water pump, and a turbulence model with the minimum test error is found based on the test; solid phases in the water pump are analyzed based on a discrete element method, and a single particle two-phase flow simulation and a high-speed photography test are compared to select a suitable solid phase mapping method; a new type of cylindrical rod chain flexible fiber model and a CFD-DEM coupling method are used to calculate two-phase flow containing fibers in the water pump; and the fiber passing performance of the water pump is preliminarily analyzed through the fiber passing time and the influence of the vortex on the fiber.The application can reveal the motion trajectory and deformation of the flexible fiber in the pump, and provides a theoretical basis for improving the fiber passing performance of the water pump.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of sewage pump design, and more particularly to a water pump two-phase flow numerical simulation method and system based on CFD-DEM. BACKGROUND

[0002] In the process of many industries and sewage treatment, the medium transported by the water pump is not pure water or liquid, but contains granular or fibrous solid materials. Compared with particles, long fibers are more likely to affect the normal operation of the water pump, and even cause damage to the water pump. At present, the research on solid-liquid two-phase flow containing fibers in China is mostly focused on the two-phase flow of fiber suspension, but fiber suspension cannot simulate the motion and deformation trajectory of flexible long fiber solid materials in the sewage pump. Therefore, it is of great practical significance to study the solid-liquid two-phase flow of the double-blade pump containing flexible long fibers.

[0003] As an important method of two-phase flow numerical simulation, CFD-DEM method has been widely used in various fields. For example, the patent with application number 202211005598.4 discloses a particle grade iron ore reduction analysis method based on CFD-DEM model. The CFD-DEM method is used for simulation, which can observe and simulate the temperature and reduction rate of any particle at any time during the reduction process, and the calculation result is more accurate. The patent with application number 202211038691.5 discloses a large particle size sand gravel stratum mud shield ring flow system centrifugal pump distribution calculation method based on CFD-DEM coupling technology. Based on the CFD-DEM coupling method, the large particle size sand gravel stratum centrifugal pump distribution is calculated quickly and accurately. However, the numerical simulation of two-phase flow containing fibers in the water pump is mostly focused on the flow of fiber suspension. For example, Kang Shun

Kang Shun. Flow characteristics of flexible fiber suspension in open impeller centrifugal paper pulp pump [D]. Jiangsu University, 2021. DOI: 10.27170 / d.cnki.gjsuu.2021.000297.

Wang Zhun. Two-phase flow containing flexible solids and forward double-blade sewage pump [D]. Jiangsu University, 2008.

[0004] Therefore, it is an urgent problem for those skilled in the art to provide a method and system capable of simulating the numerical value of the solid-liquid two-phase flow of the water pump containing long fibers. SUMMARY

[0005] Therefore, the application provides a CFD-DEM-based numerical simulation method and system for two-phase flow of a water pump.

[0006] To achieve the above object, the application provides the following technical scheme.

[0007] A CFD-DEM-based numerical simulation method for two-phase flow of a water pump comprises the following steps.

[0008] The liquid-phase flow field in the water pump is calculated according to a computational fluid dynamics method, and an optimal turbulence model is selected to generate a calculation case of the optimal turbulence model.

[0009] The CFD-DEM method based on the Fluent-Rocky bidirectional coupling is used to perform numerical simulation on the solid-liquid two-phase flow of single-particle flow in the water pump by using multiple mapping methods, and high-speed photography tests are performed to select an optimal mapping method.

[0010] The cylindrical rod chain flexible fiber model is used to model the fiber, the resistance model of the fiber in the turbulence proposed by Marheineke and Wegener is used to analyze the resistance suffered by the fiber, and the CFD-DEM coupled numerical calculation is performed on the two-phase flow containing the fiber in the water pump.

[0011] The two-phase flow numerical simulation of the water pump is post-processed, the pressure cloud map and the streamline map inside the impeller and the volute are drawn, the vortex structure characteristics of the flow field inside the pump are determined by using the Omega vortex identification method, and the vorticity map of the internal flow field is drawn; the fiber motion is compared with the pressure cloud map and the streamline map to determine that the fiber motion is affected by the vortex flow in the impeller, and the through performance of the flexible fiber in the water pump is obtained.

[0012] Before the step of calculating the liquid-phase flow field in the water pump by using the computational fluid dynamics method, the grid independence verification is further included, and the specific steps comprise:

[0013] The structured grid is used to divide the grid of the liquid-phase flow field region of the water pump, the number of divided grids is gradually increased, and multiple grid division schemes are constructed according to the different grid numbers.

[0014] The head of the water pump under the multiple grid division schemes is calculated, and the grid division scheme with less grid division number and less than 1% head error of the water pump between two adjacent times is selected to calculate the liquid-phase flow field in the water pump.

[0015] The liquid-phase flow field in the water pump is calculated according to the computational fluid dynamics method, and the optimal turbulence model is selected, which specifically comprises:

[0016] According to the computational fluid dynamics method, a plurality of turbulence models are constructed, a numerical simulation is carried out by using a Reynolds time average simulation method, and unsteady calculation is carried out on the plurality of turbulence models by using Fluent software, so as to obtain the external characteristics of the water pump under different turbulence models, and compare with the test results, select the turbulence model with the smallest error from the test results, and save the Fluent calculation case of the selected turbulence model

[0017] The optimal mapping method is selected, specifically including:

[0018] The volume diffusion method and the uniform diffusion method are used for numerical simulation of single particle flow in the water pump, and the single particle flow in the water pump is measured based on high-speed photography.

[0019] The simulation results and the test results are compared and analyzed, and the mapping method with the simulation results and the test results closer is selected.

[0020] The Fluent-Rocky two-way coupled CFD-DEM method is used for particle solid-liquid two-phase flow calculation, specifically including:

[0021] The shell of the water pump flow field area is extracted, the shell is introduced into Rocky as the wall surface of the water pump, the material properties of the wall surface and the particles are defined, the motion properties of the impeller wall surface are defined, the particle material inlet is established at the inlet of the water pump inlet extension section, the calculation case of the selected optimal turbulence model is imported into Rocky, the two-way coupled calculation model is generated, the time step and the total solution time consistent with the flow field calculation are set, and the particle two-phase flow calculation result based on the CFD-DEM method is obtained.

[0022] The cylindrical rod chain flexible fiber model is used for fiber modeling, and the specific steps are as follows:

[0023] A single fiber is regarded as a rod chain connected by N rigid cylindrical rods through spherical hinge joints, wherein the rigid cylindrical rod is called a fiber element, each cylindrical rod has a semicircular end, the cylindrical rods are connected by spherical hinge joints, the center distance of the two semicircular ends of each fiber element is l, and the circular diameter is d p The length-diameter ratio of each fiber element is r ps =l / d p The total length L of the fiber is lN, and the length-diameter ratio of the fiber is r p =L / dp.

[0024] The resistance model of the fiber in the turbulent flow proposed by Marheineke and Wegener is used to analyze the resistance of the fiber, and the steps are as follows:

[0025] According to the independence principle of the stationary flow around the cylinder, the resistance expression of the unit length on the infinite cylinder is derived:

[0026]

[0027] where p is the fluid density, d is the fiber diameter, f p is the fiber diameter, is the unit vector in the normal direction, is the unit tangent vector parallel to the axis of the spherocylinder, is the normal and tangential components of the fluid velocity relative to the spherocylinder fiber element, is the tangential component of the fluid velocity relative to the spherocylinder fiber element, C D,n is the normal drag coefficient, C D,τ is the tangential drag coefficient;

[0028] The Reynolds number Re n for the normal component of the fluid velocity relative to the spherocylinder fiber element is calculated as follows:

[0029]

[0030] where μ is the dynamic viscosity of the liquid phase; f

[0031] The coefficient r D,γ is defined as the product of the drag coefficient and Re n

[0032] r D,γ = Re n C D,γ γ = n, τ

[0033] The expression for the drag per unit length on an infinite cylinder then simplifies to:

[0034]

[0035] where r D,n is the product of the normal drag coefficient and Re n , and r D,τ is the product of the tangential drag coefficient and Re n ;

[0036] The Reynolds number Re n for the normal component of the fluid velocity relative to the fiber element in the water pump was calculated to be > 100, and according to the drag model for fibers in turbulent flow proposed by Marheineke and Wegener, r D,γ can be expressed as:

[0037]

[0038] ​​​

[0039] The CFD-DEM coupled numerical calculation of the two-phase flow containing fibers in the water pump is carried out, and the specific operation steps are as follows:

[0040] The shell of the water pump flow field is extracted, the shell is introduced into Rocky as the wall surface of the water pump, the material properties of the wall surface and the fibers are defined, the motion properties of the impeller wall surface are defined, the fiber material inlet is established at the inlet of the water pump inlet extension section, the calculation case of the selected optimal turbulence model is introduced into Rocky, a two-way coupled calculation model is generated, the time step and the total solution time consistent with the flow field calculation are set, and the calculation result of the fiber two-phase flow based on the CFD-DEM method is obtained.

[0041] The vortex structure characteristics of the internal flow field of the pump are analyzed by adopting the Omega vortex identification method; the steps of the Omega vortex identification method are as follows:

[0042] A dimensionless parameter R representing the proportion of the vortex amount of the rotating part to the total vortex amount is introduced, and the calculation formula is as follows:

[0043]

[0044] In the formula, A represents the rotational vortex, B represents the antisymmetric tensor, and ε is a positive number to ensure that the denominator is not zero;

[0045] When R=1, the fluid does rigid rotation; when R>0.5, the antisymmetric tensor B is dominant relative to A, therefore, R≥0.6 is used as the criterion for vortex identification;

[0046] In order to accurately identify the vortex flow that can affect the motion state of fibers of different sizes, and eliminate the huge error caused by the extremely small denominator, the parameter k is introduced to modify ε;

[0047]

[0048] In the formula, k is a function of the length-diameter ratio of the fiber,

[0049] On the other hand, the application also provides a water pump two-phase flow numerical simulation system based on CFD-DEM, comprising:

[0050] A liquid phase flow field model construction module for constructing a plurality of liquid phase flow field models of the liquid phase flow field in the water pump;

[0051] A solid phase model construction module comprising a particle flow field model construction unit and a fiber flow field model construction unit; for modeling the flow model of the particles and fibers contained in the water pump, respectively;

[0052] The coupling calculation module is used for coupling the liquid phase flow field model with the particle flow model and the fiber flow model respectively, generating a particle two-way coupling calculation model and a fiber two-way coupling calculation model, and setting a time step and a total solution time length consistent with the liquid phase flow field calculation, and obtaining a solid-liquid two-phase flow calculation result based on the CFD-DEM method through solution.

[0053] The analysis module is used for post-processing of the two-phase flow numerical simulation of the water pump, generating an impeller and volute internal pressure cloud chart and flow line chart, and analyzing main vortex structure characteristics of the internal flow field of the water pump to generate a vortex chart of the internal flow field; and the fiber motion affected by the vortex flow in the impeller is analyzed to preliminarily analyze the flexible fiber passing performance in the double-blade pump.

[0054] Compared with the prior art, the application provides a water pump two-phase flow numerical simulation method and system based on CFD-DEM. The internal flow field of the water pump is calculated by using the CFD method, and a turbulence model with the smallest test error is found out based on the test; the solid phase in the water pump is analyzed based on the discrete element method, and a suitable solid phase mapping method is selected by comparing and selecting a single particle two-phase flow simulation and a high-speed photography test; the two-phase flow containing the fiber in the water pump is calculated by using a new type of cylindrical rod chain flexible fiber model and a CFD-DEM coupling method; the fiber passing performance of the water pump is preliminarily analyzed by the fiber passing time and the influence of the vortex flow on the fiber. The application uses the Fluent-Rocky two-way coupling CFD-DEM method and the new type of cylindrical rod chain flexible fiber model to simulate the flow of the flexible fiber in the water pump, which can reveal the motion trajectory and deformation of the flexible fiber in the pump, and provides a theoretical basis for improving the fiber passing performance of the water pump. BRIEF DESCRIPTION OF DRAWINGS

[0055] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description only constitute the embodiments of the application, and for those skilled in the art, other drawings can also be obtained without creative labor on the basis of the provided drawings.

[0056] Figure 1 The flow chart of the water pump two-phase flow numerical simulation method based on CFD-DEM in the application;

[0057] Figure 2 The three-dimensional modeling of the double-blade centrifugal pump in the specific embodiment of the application;

[0058] Figure 3 The particle absolute motion trajectory photographed by the single particle flow high-speed photography test in the specific embodiment of the application;

[0059] Figure 4 Fiber model for specific embodiment in the present application;

[0060] Figure 5 Schematic diagram of some parameters in resistance model for specific embodiment in the present application;

[0061] Figure 6 Pressure cloud map, streamline map and vorticity map in double-blade pump impeller area for specific embodiment in the present application, wherein (a) is the pressure cloud map, (b) is the streamline map, and (c) is the vorticity map;

[0062] Figure 7 Motion deformation of fibers at different time points for double-blade centrifugal pump for specific embodiment in the present application, wherein (a) is the motion deformation of fibers at t = 0.2261 s, (b) is the motion deformation of fibers at t = 0.2793 s, (c) is the motion deformation of fibers at t = 0.4389 s, (d) is the motion deformation of fibers at t = 0.6783 s, (e) is the motion deformation of fibers at t = 1.0773 s, and (f) is the motion deformation of fibers at t = 1.4364 s. DETAILED DESCRIPTION

[0063] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0064] The embodiments of the present application take a cantilever single-stage single-suction double-blade centrifugal pump as an example for illustration. In actual application, the method and system provided by the embodiments of the present application can also be applied to various forms of centrifugal pumps, such as vertical, horizontal, single-stage, multi-stage, single-suction, double-suction, self-priming, etc.

[0065] As shown in Figure 1 , the embodiments of the present application provide a control method of a virtual reality scene,

[0066] A certain cantilever single-stage single-suction double-blade centrifugal pump has a specific speed n s = 111, a flow rate Q = 25.86 m3 / h, a head H = 2.68 m, and a rotational speed n = 750 r / min.

[0067] (1) The CFD method is used to calculate the liquid phase flow field in the double-blade pump.

[0068] A three-dimensional model of the double-blade pump is established, as shown in Figure 2The grid independence analysis is shown in Table 1. The structured grid is used to divide the flow field area of the double- blade pump. Multiple grid schemes are divided according to the number of grids. The number of grids and the calculated head of different grid schemes are given in Table 1. According to Table 1, with the continuous increase of the total number of grids, the predicted value of the model pump head tends to be stable. In order to improve the calculation efficiency, the third set of grids is selected for numerical calculation.

[0069] Table 1 Grid independence analysis

[0070]

[0071] In the Fluent software, different turbulence models such as standard k-ε, RNG k-ε, k-ω, SST k-ω are used for unsteady calculation. The calculation is carried out once every four degrees of impeller rotation, the time step is set to Δz = 0.0133s, the calculation step is 3000 steps, and the total calculation time is Z = 3.99s. The external characteristics of the double- blade pump under different turbulence models are compared with the test results. It is found that when the standard k-ε turbulence model is used for calculation, the error between the calculated results and the test results of the external characteristics at the rated condition is less than 1%, the deviation of the energy performance predicted by CFD is less than 1%, and the error is the smallest. Therefore, the standard k-ε turbulence model is used for liquid phase numerical calculation. Table 2 is the numerical calculation and test external characteristic data under rated condition using different turbulence models.

[0072] Table 2 Numerical calculation and test external characteristic data under rated condition

[0073]

[0074]

[0075] (2) Based on the discrete element method, the CFD-DEM method of Fluent-Rocky two-way coupling is used for solid-liquid two-phase flow calculation. Two mapping methods of volume diffusion method and uniform diffusion method are used for numerical simulation of single particle flow in double- blade pump. The shell of the double- blade pump flow field area is extracted, and the shell is introduced into Rocky as the wall surface of the double- blade pump. The wall surface material density is set to 7850kg / m 3 , Young's modulus is 1×10 11 N / m 2 ; the particle is set as a spherical particle with a diameter of 6mm, and the particle density is 1200kg / m 3, solid phase mapping method respectively using volume diffusion method and uniform diffusion method. In the double blade pump inlet extension section entrance to establish solid phase material entrance, set the impeller wall surface rotation speed 750 r / min. The flow field calculation of Fluent in step (1) is saved as a calculation case file and imported into Rocky to generate a two-way coupled calculation model. Set the time step Δz r = 0.133 s, that is, Fluent transmits data to Rocky once every ten steps, and the total time is the same as the liquid phase calculation, and the two-phase flow of single particle flow is solved.

[0076] High-speed photography test of single particle flow in double blade pump, Figure 3 The absolute trajectory of the single particle is shot for the test. The simulation results are compared with the test results, which proves that the numerical simulation results using the volume diffusion method are closer to the test results, so the volume diffusion method is used for calculation.

[0077] (3) A new type of cylindrical rod chain flexible fiber model is used to model the fiber.

[0078] A flexible fiber model with fiber length L = 200 mm and fiber diameter d p = 5 mm is established, as shown in Figure 4 The model is connected by 20 rigid fiber elements with the same length, and the length of each fiber element is l = 10 mm. The two ends of the fiber element are semicircular spherical type, and the cylindrical rods are connected by spherical hinge joints. The length-diameter ratio of each fiber element is r ps = 2, and the length-diameter ratio of the fiber is r p = 40.

[0079] The fiber material density is set to ρ p = 439 kg / m 3 , and the Young's modulus is 1 × 10 7 N / m 2 .

[0080] The Multiple Elements setting is used for the fiber model, that is, each fiber element is regarded as a single element, that is, each fiber is composed of 20 elements, and the volume diffusion method is selected for the mapping method. At the same time, the resistance model of the fiber in the turbulent flow proposed by Marheineke and Wegener is used to analyze the resistance of the fiber:

[0081] According to the independence principle of stationary flow around a cylinder, the resistance expression of unit length on an infinite cylinder is derived:

[0082]

[0083] In the formula: ρf is the fluid density, dp is the fiber diameter, is the unit vector in the normal direction, is the tangential unit vector parallel to the cylinder axis, is the normal component and is the tangential component of the fluid velocity relative to the cylinder fiber element, is the tangential component of the fluid velocity relative to the cylinder fiber element, C D,n is the normal drag coefficient, C D,τ is the tangential drag coefficient. Figure 5 is the schematic diagram of some parameters in the formula.

[0084] The Reynolds number Renof the normal component of the fluid velocity relative to the cylinder fiber element is calculated as follows:

[0085]

[0086] where: μ f is the dynamic viscosity of the liquid phase.

[0087] The coefficient r D,γ is defined as the product of the drag coefficient and Re n :

[0088] r D,γ = Re n C D,γ γ = n, τ

[0089] Then the drag expression of unit length on the infinite cylinder is simplified as:

[0090]

[0091] where: r D,n is the product of the normal drag coefficient and Re n , and r D,τ is the product of the tangential drag coefficient and Re n .

[0092] According to the Reynolds number calculation formula and the inlet flow velocity of the double-blade pump, the Reynolds number Re n of the normal component of the fluid velocity relative to the fiber element in the double-blade pump is calculated. When Re n > 100, according to the drag model of the fiber in the turbulent flow proposed by Marheineke and Wegener, it can be deduced that when Re D,γ > 100, r D,τ expression is as follows:

[0093]

[0094]

[0095] The wall material density is set to 7850 kg / m 3 , and the Young's modulus is 1 × 10 11 N / m2 The fiber inlet is arranged in the pump inlet extension section, and the fiber mass flow rate is set to 0.001724 kg / min (simulating the flow of a single fiber in the pump). The wall surface rotation speed of the impeller is set to 750 r / min. The flow field calculation of Fluent in step (1) is saved as a calculation case file and imported into Rocky to generate a two-way coupled calculation model. The time step Δt is set to 0.133 s, i.e., Fluent transmits data to Rocky once every ten steps, and the total time is the same as the liquid phase calculation. After the settings are completed, the CFD-DEM coupled numerical calculation of the two-phase flow containing fibers in the double-blade pump is performed. r

[0096] (4) The numerical simulation of the two-phase flow containing fibers in the double-blade pump is post-processed, and the pressure cloud map and streamline map inside the impeller and volute are drawn. The Omega vortex identification method is used to analyze the main vortex structure characteristics of the internal flow field of the pump, and the vorticity map of the internal flow field is drawn. The steps of using the Omega vortex identification method for analysis are as follows:

[0097] A dimensionless parameter R representing the proportion of the rotational part of the vorticity to the total vorticity is introduced, and its calculation formula is:

[0098]

[0099] In the formula, A represents the rotational vorticity, B represents the antisymmetric tensor, and ε is a small positive number to ensure that the denominator is not zero.

[0100] When R = 1, the fluid is in rigid rotation; when R > 0.5, the antisymmetric tensor B is equivalent to A. R ≥ 0.6 is used as the criterion for vortex identification.

[0101] In order to accurately identify the vortex that can affect the motion state of fibers of different sizes, and at the same time eliminate the huge error caused by the extremely small denominator, the parameter k is introduced to modify ε:

[0102]

[0103] In the formula, k is a function of the length-diameter ratio of the fiber,

[0104] According to the calculation, R = 0.62 is selected as the threshold for vortex identification in this embodiment. Figure 6 The pressure cloud map, streamline map, and vorticity map in the impeller region of the double-blade pump are shown.

[0105] The motion and deformation of the flexible fiber in the impeller and volute at different time nodes are obtained by taking the time when the flexible fiber enters the impeller as the starting time point and the time when the flexible fiber completely flows out of the volute as the ending time point. Figure 7 ​The motion and deformation of the fiber at different time points (t=0s, t=0.0133s, 0.2261s, 0.2793s, 0.6783s, 1.0773s, 1.4364s, respectively) are calculated. The fiber motion at different time points is compared with the pressure cloud chart and the streamline chart to analyze the influence of the vortex flow in the impeller on the fiber motion. The through performance of the flexible fiber in the double-blade pump is preliminarily analyzed through the fiber passing time and the influence of the vortex flow on the fiber.

[0106] In another aspect, the present application also provides a CFD-DEM-based two-phase flow numerical simulation system of a water pump, comprising:

[0107] A liquid phase flow field model construction module is configured to construct liquid phase flow field models of liquid phase flow fields in multiple water pumps.

[0108] A solid phase model construction module comprises a particle flow field model construction unit and a fiber flow field model construction unit, and is configured to model the flow models of particles and fibers contained in the water pump, respectively.

[0109] A coupling calculation module is configured to couple the liquid phase flow field model with the particle flow model and the fiber flow model, respectively, to generate a particle bidirectional coupling calculation model and a fiber bidirectional coupling calculation model, and set a time step and a total solution time length consistent with the liquid phase flow field calculation, and solve to obtain a solid-liquid two-phase flow calculation result based on the CFD-DEM method.

[0110] An analysis module is configured to post-process the two-phase flow numerical simulation of the water pump, generate a pressure cloud chart and a streamline chart of the impeller and the volute, analyze the main vortex structure characteristics of the flow field in the pump, generate a vorticity chart of the internal flow field, analyze the influence of the vortex flow in the impeller on the fiber motion, and preliminarily analyze the through performance of the flexible fiber in the double-blade pump.

[0111] The embodiments in the specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts of each embodiment can be referred to each other. For the device disclosed in the embodiments, since it corresponds to the method disclosed in the embodiments, the description is relatively simple, and the related parts can be referred to the method part.

[0112] The above description of the disclosed embodiments enables a person skilled in the art to implement or use the present application. Various modifications to the embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A CFD-DEM based numerical simulation method of two-phase flow in a water pump, characterized in that, The method comprises the following steps: The liquid phase flow field in the water pump is calculated according to the computational fluid dynamics method, and an optimal turbulence model is selected to generate a calculation case of the optimal turbulence model; Based on the CFD-DEM method of Fluent-Rocky two-way coupling, a plurality of mapping methods are used to perform numerical simulation on single particle flow in the water pump, and a high-speed photography test is performed to select an optimal mapping method; A cylindrical rod chain flexible fiber model is used to model the fiber, a resistance model of the fiber in turbulence proposed by Marheineke and Wegener is used to analyze the resistance of the fiber, and CFD-DEM coupled numerical calculation is performed on the two-phase flow containing the fiber in the water pump; The two-phase flow numerical simulation of the water pump is post-processed, the pressure cloud map and the streamline map inside the impeller and the volute are drawn, the vortex structure characteristics of the flow field inside the pump are determined by using the Omega vortex identification method, and the vortex map of the internal flow field is drawn; the fiber motion is compared with the pressure cloud map and the streamline map to determine that the fiber motion is affected by the vortex flow in the impeller, and the flexible fiber passing performance in the water pump is obtained; The liquid phase flow field in the water pump is calculated according to the computational fluid dynamics method, and an optimal turbulence model is selected to generate a calculation case of the optimal turbulence model, specifically including: The liquid phase flow field in the water pump is calculated according to the computational fluid dynamics method, and an optimal turbulence model is selected, specifically including: A plurality of turbulence models are constructed according to the computational fluid dynamics method, numerical simulation is performed by using the Reynolds time average simulation method, and the Fluent software is used to perform unsteady calculation on the plurality of turbulence models to obtain the external characteristics of the water pump under different turbulence models, and the test results are compared to select the turbulence model with the smallest error and save the Fluent calculation case of the selected turbulence model; The resistance model of the fiber in turbulence proposed by Marheineke and Wegener is used to analyze the resistance of the fiber, and the steps are as follows: According to the independence principle of stationary flow around a cylinder, the resistance expression of unit length on the infinite cylinder is derived as follows: wherein: Then the resistance expression of unit length on the infinite cylinder is simplified as: f is the fluid density, d p is the fiber diameter, is the unit vector in the normal direction, is the unit tangent vector parallel to the axis of the spherocylinder, is the normal and tangential components of the velocity of the fluid relative to the spherocylinder fiber element, is the tangential component of the velocity of the fluid relative to the spherocylinder fiber element, C D,n is the normal drag coefficient, C D,τ is the tangential drag coefficient; Reynolds number Re of the normal component of the fluid relative to the velocity of the spherocylindrical fiber n The calculation formula is as follows: In the formula: The optimal mapping method is selected, specifically including: f is the liquid dynamic viscosity coefficient; The coefficients r D,γ defined as the product of the drag coefficient and Re n : The volume diffusion method and the uniform diffusion method are used to simulate the single particle flow in the water pump, and the single particle flow in the water pump is measured based on high-speed photography; wherein: r D,n is the product of the normal drag coefficient and Re n r D,τ is the product of the tangential drag coefficient and Re n is the product of the tangential drag coefficient and Re​ The Reynolds number Re of the normal component of the fluid velocity relative to the fiber element in the water pump was calculated according to the Reynolds number calculation formula n >100, the resistance model of the fiber in the turbulent flow proposed by Marheineke and Wegener can be derived that when Re n >100, r D,γ The expression is as follows: ； The simulation results and the test results are compared and analyzed, and the mapping method with the simulation results closer to the test results is selected. Before the step of calculating the liquid phase flow field in the water pump by using the computational fluid dynamics method, the grid independence verification is further included, and the specific steps include: The structured grid is used to divide the grid of the liquid phase flow field region of the water pump, the number of divided grids is gradually increased, and a plurality of grid division schemes are constructed according to the different grid numbers; 2. The CFD-DEM based numerical simulation method of two-phase flow in a water pump according to claim 1, characterized in that, The head of the water pump under the plurality of grid division schemes is calculated, and the grid division scheme with the grid division number less than the grid division scheme with the head error of the water pump less than 1% between two adjacent times is selected to calculate the liquid phase flow field in the water pump. The CFD-DEM method of Fluent-Rocky two-way coupling is used to calculate the particle solid-liquid two-phase flow, specifically including: ​ 3. The CFD-DEM based two-phase flow numerical simulation method of a water pump according to claim 1, characterized in that, ​ The shell of the water pump flow field region is extracted, the shell is introduced into Rocky as the wall surface of the water pump, the material properties of the wall surface and the particles are defined, the motion properties of the impeller wall surface are defined, the particle material inlet is established at the inlet of the water pump inlet extension section, the calculation case of the selected optimal turbulence model is introduced into Rocky, a two-way coupling calculation model is generated, the time step and the total solution time consistent with the flow field calculation are set, and solution is performed to obtain the particle two-phase flow calculation result based on the CFD-DEM method.

4. The CFD-DEM based numerical simulation method of two-phase flow in a water pump according to claim 1, characterized in that, The flexible fiber model of the cylindrical rod chain is adopted to model the fiber, and the specific steps are as follows: A single fiber is regarded as a chain of rigid cylindrical rods connected by spherical hinge joints, where the rigid cylindrical rods are called fiber elements, each cylindrical rod has a semicircular end at both ends, the cylindrical rods are connected by spherical hinge joints, the center distance of the two semicircular ends of each fiber element is N , and the circular diameter is l d p The length-diameter ratio of each fiber element is r ps =l / d p The total length of the fiber is L = lN , and the length-diameter ratio of the fiber is r p = L / dp .​ 5. The CFD-DEM based numerical simulation method of two-phase flow in a water pump according to claim 1, wherein, The CFD-DEM coupling numerical calculation of the two-phase flow in the water pump containing the fiber is performed, and the specific operation steps are as follows: The shell of the water pump flow field region is extracted, the shell is introduced into Rocky as the wall surface of the water pump, the material properties of the wall surface and the particles are defined, the motion properties of the impeller wall surface are defined, the particle material inlet is established at the inlet of the water pump inlet extension section, the calculation case of the selected optimal turbulence model is introduced into Rocky, a two-way coupling calculation model is generated, the time step and the total solution time consistent with the flow field calculation are set, and solution is performed to obtain the particle two-phase flow calculation result based on the CFD-DEM method.

6. The CFD-DEM based numerical simulation method of two-phase flow in a water pump according to claim 1, wherein, The Omega vortex identification method is adopted to analyze the vortex structure characteristics of the internal flow field of the pump, and the steps of the Omega vortex identification method are as follows: A non-dimensional parameter is introduced to represent the proportion of the rotational component of vorticity to the total vorticity R whose calculation formula is: wherein: A represents the rotational vorticity, B represents the anti-symmetric tensor, ε is a positive number to ensure that the denominator is not zero; When R =1, the fluid does rigid rotation; R >0.5 represents an antisymmetric tensor B with respect to A prevails, therefore, the adoption R ≥0.6 as a criterion for vortex identification; In order to accurately identify the eddy current which can affect the motion state of fibers of different sizes, and eliminate the huge error caused by the denominator being a very small number, the parameter k is introduced ε is corrected; In the formulae: k is a function of the fiber aspect ratio, .

7. A system for implementing a CFD-DEM based numerical simulation method of two-phase flow in a water pump according to any one of claims 1-6, characterized in that, Comprise: The liquid phase flow field model construction module is used for constructing the liquid phase flow field model of the plurality of water pumps. The solid phase model construction module comprises a particle flow field model construction unit and a fiber flow field model construction unit, and is used for modeling the flow model of the particles and the fibers contained in the water pump, respectively. The coupling calculation module is used for coupling the liquid phase flow field model with the particle flow model and the fiber flow model, respectively, to generate a particle two-way coupling calculation model and a fiber two-way coupling calculation model, and set the time step and the total solution time consistent with the liquid phase flow field calculation, and perform solution to obtain the solid-liquid two-phase flow calculation result based on the CFD-DEM method. The analysis module is used for post-processing of the two-phase flow numerical simulation of the water pump, generating the pressure cloud map and the streamline map inside the impeller and the volute, analyzing the main vortex structure characteristics of the internal flow field of the pump, and generating the vorticity map of the internal flow field; analyzing the influence of the vortex flow in the impeller on the fiber motion, and preliminarily analyzing the through performance of the flexible fiber in the double-blade pump.

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