Optimization method for post-mixed ice abrasive jet nozzle

Abstract

The post-mixed ice abrasive jet nozzle optimization method comprises the steps that basic parameters of a nozzle to be optimized are obtained, and a CFD model for a continuous phase is constructed; establishing an ice particle database, and establishing a DEM model for a discrete phase based on data in the ice particle database; coupling is carried out based on the CFD model and the DEM model, a CFD-DEM coupling model is obtained, and the CFD-DEM coupling model is verified; constructing an ice particle phase change model by adopting a lattice Boltzmann method to simulate heat exchange characteristics, and simplifying the verified CFD-DEM coupling model based on the ice particle phase change model; based on the simplified CFD-DEM coupling model, flow state analysis of solid-state two-phase flow and wear analysis of a nozzle are carried out; a nozzle is optimized according to a flow state analysis result and a wear analysis result, theoretical support is provided for optimizing a jet flow process and nozzle design, meanwhile, an ice particle phase change model is established by introducing a lattice Boltzmann method, the reasonability of the ice particle phase change model is verified through numerical simulation, a CFD-DEM coupling model is simplified while the calculation precision is guaranteed, and the calculation complexity is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of nozzle optimization, in particular to a post-mixing ice abrasive jet nozzle optimization method. BACKGROUND

[0002] In the process of mariculture, net cages are often used as breeding equipment. In the long-term breeding process, a large amount of impurities and dirt such as algae, barnacles and shellfish will adhere to the net clothes of the net cage. In order to ensure the normal flow of water inside and outside the net cage, the net clothes of the net cage need to be cleaned regularly. The commonly used cleaning tool is a jet nozzle, which sprays jet liquid to the net clothes to achieve cleaning. In order to improve the cleaning effect, an abrasive jet nozzle is often used, that is, abrasive is added to the nozzle, and the impact force of the abrasive when it is sprayed out is used to break the shellfish and remove filamentous algae. The commonly used abrasive jet is divided into pre-mixed and post-mixed abrasive jet. The pre-mixed abrasive jet mixes the abrasive and water uniformly in the abrasive tank in advance, and then sprays them out under pressure. The post-mixed abrasive jet uses the negative pressure formed by the Venturi effect to suck the abrasive into the mixing chamber for acceleration. The pre-mixed abrasive jet has the advantages of fully mixed abrasive and water before entering the nozzle, high jet concentration, stable processing process and good surface quality. However, the pre-mixed abrasive jet has the disadvantages of short service life of high-pressure pipeline and nozzle due to easy wear. The post-mixed abrasive jet has the advantages of simple structure, low cost, easy maintenance and less wear of high-pressure water pipe, and is widely used.

[0003] In order to avoid pollution to the marine environment, ice abrasive jet technology replaces traditional abrasives such as sand and steel balls with ice particles as natural low-temperature abrasives. Ice particles have low hardness and brittleness, can form a mild impact force in the cleaning process to protect the net clothes, and can naturally melt during the operation process to fundamentally eliminate secondary pollution to the marine ecosystem. The nozzle is the core component of the abrasive water jet system, and the wear of the inner wall of the nozzle directly affects the stability of the jet, the cleaning efficiency and accuracy. This wear is caused by the repeated impact and erosion of the abrasive on the inner wall of the nozzle, which gradually changes the geometry of the nozzle and eventually leads to significant degradation of the jet performance. However, in the current research on ice abrasive jet, the exploration of the internal flow field characteristics and wear mechanism of the nozzle is still in the initial stage, and effective technical support for nozzle structure optimization and prolonging its service life has not been provided. SUMMARY

[0004] In view of this, the present application provides a post-mixing ice abrasive jet nozzle optimization method, which can optimize the jet performance of the post-mixing ice abrasive jet nozzle and prolong the service life of the nozzle.

[0005] The technical solution of the present application is as follows: A post-mixing ice abrasive jet nozzle optimization method, comprising the following methods: Step S1, obtaining the basic parameters of the nozzle to be optimized, and constructing a CFD model for the continuous phase; Step S2, establishing an ice particle database, and establishing a DEM model for the discrete phase based on the data in the ice particle database; Step S3, coupling based on the CFD model and the DEM model, obtaining a CFD-DEM coupling model, and verifying the CFD-DEM coupling model; Step S4, constructing an ice particle phase change model to simulate heat exchange characteristics by using the lattice Boltzmann method, and simplifying the verified CFD-DEM coupling model based on the ice particle phase change model; Step S5, performing flow state analysis and nozzle wear analysis of the solid two-phase flow based on the simplified CFD-DEM coupling model; Step S6, optimizing the nozzle according to the flow state analysis result and the wear analysis result.

[0006] Preferably, the specific steps of step S1 are as follows: Obtaining the inlet end parameters, internal channel parameters and outlet end parameters of the nozzle to be optimized as the basic parameters; Constructing a continuity equation based on the basic parameters: The initial continuity equation is constructed as: Wherein , , respectively represent the velocity components of the fluid, is the fluid density, is the time, , , are three coordinate axes of the spatial rectangular coordinate system; Substitute operator: , , , , are unit vectors in the positive direction of the x-axis, y-axis and z-axis respectively, is the velocity vector of the fluid, when calculating the incompressible flow, the fluid density is a constant, and the initial continuity equation becomes: ; Constructing a momentum conservation equation based on the basic parameters: Based on the principle of momentum conservation, the momentum conservation equations in X, Y and Z directions are derived: ; ; ; Wherein represents static pressure, represents external force in the direction, represents stress tensor; Based on the basic parameters, the energy conservation equation is constructed: where T is the temperature, is the heat transfer coefficient, is the internal heat source containing fluid and the part of mechanical energy converted into heat energy, is the divergence operator, is the temperature gradient, is the constant volume specific heat capacity of the fluid; Adopt The turbulence model is constructed based on the basic parameters: ; ; where the effective viscosity , represents the molecular viscosity, and the turbulent viscosity , is the fluid density, is the turbulent kinetic energy dissipation rate, represents the turbulent kinetic energy, is a dimensionless empirical constant, is the turbulent energy term caused by the velocity difference and the buoyancy, and represent the Prandtl number of k and , reflects the influence of turbulence on the total dissipation rate, , , is an empirical constant, and R is the correction of the dissipation term caused by the Reynolds stress.

[0007] Preferably, the specific steps of step S2 are: An ice particle collision model containing ice particle mass, damping coefficient and elastic coefficient is established: where , is the mass and displacement of the oscillator, c, is the damping coefficient and elastic coefficient, is the relative acceleration and relative velocity, respectively; When the ice particles collide, the normal overlap is: where and are the vector positions of the sphere centers, and are the radii of particle i and particle j, respectively; The contact radius between ice particles is: , ; The normal contact force between ice particles is , ,in , are the elastic moduli of ice particles i and j, 、 are the Poisson's ratios of ice particles i and j, respectively; The normal damping force is: , ,in , the expression is:

[0008] are the masses of particle i and particle j respectively, is the relative normal velocity of ice particles i and j: , The velocity vectors of particles 1 and 2, and n is the normal unit vector when the ice particles collide: , and are the vector positions of the sphere center; Tangential force between ice particles for: ,in is the tangential overlap, is the tangential stiffness: , where G* is the equivalent shear modulus:

[0009] In the formula 、 are the shear moduli of material i and material j respectively; The tangential damping force after ice particle collision is:

[0010] Establish the motion control equation of ice particles: , , ; in is the acceleration of the t-th particle in the x direction, and the resistance force on the ice particle is ; is the relaxation time; is the particle size; 、 is the velocity of the fluid and ice particles; are the density of ice particles and the viscosity of the fluid respectively; is the ice particle Reynolds number, is the drag coefficient, and g is the gravity acceleration, and F is the other force acting on the particle except the drag force and buoyancy force, and the drag coefficient is calculated by the following formula for spherical ice particles:

[0011] The erosion wear model is established by using the Oka model:

[0012]

[0013]

[0014]

[0015] wherein , are the hardness of the nozzle surface material and the wall surface area, respectively; , are the ice particle velocity and diameter, respectively; is the wear caused by an arbitrary impact angle; , are the velocity and diameter of the reference ice particle, respectively; and g(α) is a function of the impact angle α; is the mass flow rate; and K, a, b, k1, k2, k3, n1, and n2 are constants.

[0016] Preferably, the specific steps of the step S3 are as follows: Step S31, the flow field of one time step is calculated by using the CFD model and iterated to convergence; Step S32, the DEM model starts the calculation of the ice particle phase, and the force and movement of the ice particle are calculated according to the flow field data; Step S33, after the position of the ice particle is updated, the force of the ice particle on the liquid phase is added to the flow field calculation, and the steps S31-S33 are cycled to obtain the CFD-DEM coupling model; Step S34, the conical nozzle model and the 90° elbow model are used to verify the flow characteristics and the wear of the CFD-DEM coupling model, respectively.

[0017] Preferably, the specific steps of the step S4 are as follows: A physical model of the post-mixed abrasive jet nozzle is constructed, the physical model of the post-mixed abrasive jet nozzle comprising a high-pressure water pipeline, a mixing chamber, a contraction transition section, and a focusing tube connected in sequence, and a feeding pipe is arranged on the mixing chamber; The LBM model is constructed by using the lattice Boltzmann method, the minimum speed of ice particles at the outlet of a physical model of a post-mixing abrasive jet nozzle and the time-averaged speed at the outlet of a flow field are selected as boundary conditions of the LBM model, the LBM model is simplified into a uniform heat flow field, and the ice particles are fixed at the center of the flow field; By dimensionless processing, the velocity field, temperature field and volume fraction cloud chart around the ice particles under different Reynolds numbers are calculated by using the LBM model for analysis, and the CFD-DEM coupling model verified is simplified based on the analysis result.

[0018] Preferably, the dimensionless processing includes dimensionless processing of the velocity, temperature, length and time, specifically: , , , ; Among them, , , , are dimensionless velocity, temperature, length and time respectively; , , are actual velocity, temperature and length respectively; , are characteristic velocity and characteristic temperature; D is the particle size of the ice particles; N is the calculation time step, and d is the number of lattices occupied by the ice particles.

[0019] Preferably, the specific steps of the step S5 of performing flow state analysis of the solid two-phase flow are: determining the variables as the length-diameter ratio of the mixing chamber, the abrasive incidence angle, the abrasive particle size and the abrasive mass flow rate; determining the affected factors as the nozzle flow field and pressure distribution, the abrasive mass concentration distribution, the abrasive spatial position distribution and the abrasive velocity distribution; adopting the control variable method to compare and analyze the influence of different variables on the affected factors by using the CFD-DEM coupling model, so as to obtain the flow state analysis result.

[0020] Preferably, the specific steps of the step S5 of performing wear analysis of the nozzle are: determining the variables as the length-diameter ratio of the mixing chamber, the abrasive incidence angle, the abrasive particle size and the abrasive mass flow rate; determining the affected factors as the normal and tangential cumulative energy and the Oka wear distribution; adopting the control variable method to compare and analyze the influence of different variables on the affected factors by using the CFD-DEM coupling model, so as to obtain the wear analysis result.

[0021] Preferably, the length-diameter ratio of the mixing chamber of the nozzle, the abrasive incidence angle, the abrasive particle size and the abrasive mass flow are optimized according to the flow state analysis result and the wear analysis result.

[0022] Compared with the prior art, the present application has the following advantages: The method comprises the following steps: constructing a CFD model and a DEM model by simulating continuous phase and discrete phase of the nozzle; combining the CFD model and the DEM model to obtain a CFD-DEM coupling model; introducing a lattice Boltzmann method to construct an ice particle phase change model to verify the influence of the phase change effect of the ice particles on the overall model, so as to simplify the subsequent calculation of the CFD-DEM coupling model and ensure the feasibility of the numerical calculation; and performing flow state analysis and wear analysis of the nozzle by using the CFD-DEM coupling model, so as to optimize the nozzle according to the analysis result, thereby optimizing the jet process and prolonging the service life of the jet nozzle. BRIEF DESCRIPTION OF DRAWINGS

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced as follows. Obviously, the drawings in the following description are only preferred embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0024] Figure 1 The flow chart of the method for optimizing the post-mixing ice abrasive jet nozzle of the present application; Figure 2 The main technical route map of the method for optimizing the post-mixing ice abrasive jet nozzle of the present application; Figure 3 The schematic diagram of the coupling of the CFD model and the DEM model of the method for optimizing the post-mixing ice abrasive jet nozzle of the present application; Figure 4 The schematic diagram of the physical model of the post-mixing abrasive jet nozzle of the method for optimizing the post-mixing ice abrasive jet nozzle of the present application; Figure 5 The velocity distribution nephogram under different Reynolds numbers calculated by the LBM model of the method for optimizing the post-mixing ice abrasive jet nozzle of the present application; Figure 6 The temperature distribution nephogram under different Reynolds numbers calculated by the LBM model of the method for optimizing the post-mixing ice abrasive jet nozzle of the present application; Figure 7A post-mixing ice abrasive jet nozzle optimization method provided by the application utilizes an LBM model to calculate ice particle volume cloud maps under different Reynolds numbers; Figure 8 The ice particle volume fraction-time change curves under different Reynolds numbers; Figure 9 The ice particle melting volume fraction maps under different Reynolds numbers; DETAILED DESCRIPTION In order to better understand the technical content of the application, a specific embodiment is provided below, and the application is further described in combination with the accompanying drawings.

[0025] Referring to Figures 1 to 2 The post-mixing ice abrasive jet nozzle optimization method provided by the application comprises the following methods: Step S1, obtaining the basic parameters of the nozzle to be optimized, and constructing a CFD model for the continuous phase; Step S2, establishing an ice particle database, and establishing a DEM model for the discrete phase based on the data in the ice particle database; Step S3, coupling based on the CFD model and the DEM model, obtaining a CFD-DEM coupling model, and verifying the CFD-DEM coupling model; Step S4, constructing an ice particle phase change model to simulate heat exchange characteristics by using the lattice Boltzmann method, and simplifying the verified CFD-DEM coupling model based on the ice particle phase change model; Step S5, performing flow state analysis of solid two-phase flow and wear analysis of the nozzle based on the simplified CFD-DEM coupling model; Step S6, optimizing the nozzle according to the flow state analysis result and the wear analysis result.

[0026] The present invention is applied to a post-mixed abrasive jet nozzle in which the abrasive is ice particles. In order to further optimize the nozzle, it is necessary to analyze the flow state and wear of the solid two-phase flow of the ice abrasive in the jet nozzle, so as to optimize the nozzle design process and structure and extend the service life of the nozzle. When optimizing, first, a CFD model for the continuous phase is constructed based on the basic parameters of the nozzle to be optimized, wherein the continuous phase is a fluid containing a single liquid or a liquid containing solids. At the same time, an ice particle database is constructed based on the ice particles used as abrasives, and parameters are obtained from the ice particle data to construct a DEM model for the discrete phase. The discrete phase refers to a single ice particle. In the abrasive jet, changes in the discrete phase will affect the continuous phase. Therefore, a coupled simulation of the continuous phase and the discrete phase is required. Therefore, after coupling the CFD model and the DEM model, a CFD-DEM coupled model can be obtained. , and use some existing physical models to verify the CFD-DEM coupling model, verifying the reliability of the CFD-DEM coupling model in flow analysis and wear analysis. Since the abrasive uses ice particles, the phase change phenomenon of the ice particles will significantly increase the complexity of the numerical simulation. Therefore, the present invention introduces the lattice Boltzmann method, establishes an ice particle phase change model, and performs analysis based on the ice particle phase change model. The analysis results show that the ice particle phase change can be ignored, thereby simplifying the subsequent calculation process of the CFD-DEM coupling model and reducing the complexity of the numerical simulation. Finally, the CFD-DEM coupling model can be used to perform flow analysis of solid two-phase flow and wear analysis of the nozzle respectively. Based on the analysis results, the preparation process and structure of the nozzle can be optimized to increase the ice particle speed, improve the net cleaning effect, reduce wear, and extend the service life of the nozzle.

[0027] Preferably, the specific steps of step S1 are: Obtaining the inlet end parameters, internal channel parameters and outlet end parameters of the nozzle to be optimized as basic parameters; Construct the continuity equation based on the basic parameters: The initial continuity equation is constructed as: ,in 、 、 represent the velocity components of the fluid, is the fluid density, For time, 、 、 are the three coordinate axes of the spatial rectangular coordinate system; Bring in Operator: , , 、 、 are the unit vectors in the positive directions of the x-axis, y-axis, and z-axis respectively. is the velocity vector of the fluid. When calculating incompressible flow, the fluid density is a constant, the initial continuity equation becomes: ; Construct the momentum conservation equation based on basic parameters: Based on the principle of conservation of momentum, the momentum conservation equations in the X, Y, and Z directions are derived: ; ; ; in Indicates static pressure, express External force in the direction, represents the stress tensor; Construct the energy conservation equation based on basic parameters: , where T is the temperature, is the heat transfer coefficient, It is the part that contains the internal heat source of the fluid and the part that converts mechanical energy into thermal energy. is the divergence operator, is the temperature gradient, is the constant pressure specific heat capacity of the fluid; use The model builds a turbulence model based on basic parameters: ; ; The effective viscosity , Indicates molecular viscosity, turbulent viscosity , is the fluid density, is the turbulent kinetic energy dissipation rate, represents the turbulent kinetic energy, is a dimensionless empirical constant, is the turbulent energy term caused by velocity difference and buoyancy, and Represent k and The Prandtl number, reflects the effect of turbulence on the total dissipation rate, 、 、 is an empirical constant, and R is the correction of the dissipation term caused by Reynolds stress.

[0028] Preferably, the specific steps of step S2 are: Create an ice particle collision model that includes the mass, damping coefficient, and elastic coefficient of the ice particles: ,in 、 is the mass and displacement of the oscillator, c, are the damping coefficient and elastic coefficient, are relative acceleration and relative velocity respectively; When the ice particles collide, the normal overlap is: ,in and is the vector position of the sphere's center, and are the radii of particles i and j respectively; The contact radius between ice particles is: , ; The normal contact force between ice particles is , ,in , are the elastic moduli of ice particles i and j, 、 are the Poisson's ratios of ice particles i and j, respectively; The normal damping force is: , ,in , the expression is:

[0029] are the masses of particle i and particle j respectively, is the relative normal velocity of ice particles i and j: , The velocity vectors of particles 1 and 2, and n is the normal unit vector when the ice particles collide: , and are the vector positions of the sphere center; Tangential force between ice particles for: ,in is the tangential overlap, is the tangential stiffness: , where G* is the equivalent shear modulus:

[0030] In the formula 、 are the shear moduli of material i and material j respectively; The tangential damping force after ice particle collision is:

[0031] Establish the motion control equation of ice particles: , , ; where the resistance experienced by the ice particle is ; is the relaxation time; is the particle diameter; , is the velocity of the fluid and the ice particle; is the density of the ice particle and the viscosity of the fluid, respectively; is the ice particle Reynolds number, is the drag coefficient, and is the gravitational acceleration and other forces experienced by the particle in addition to the drag force, buoyant-gravity, respectively, for a spherical ice particle, the drag coefficient is calculated by the following equation:

[0032] An erosion wear model is established using the Oka model:

[0033]

[0034]

[0035]

[0036] where , is the hardness of the nozzle surface material and the wall surface area, respectively; , is the ice particle velocity and diameter; is the wear caused by an arbitrary impact angle; , is the reference ice particle velocity and diameter; g(α) is a function of the impact angle α; is the mass flow rate; K, a, b, k1, k2, k3, n1, n2 are constants.

[0037] In the discrete element method, according to the contact mode, it can be divided into hard sphere model and soft sphere model, the hard sphere model is mainly used for the simulation of high-speed particle motion, the key is to describe the instantaneous collision between particles, and it is assumed that the particles have no significant plastic deformation when colliding, in contrast, the soft sphere model is more suitable for the simulation of multi-particle collision, and it shows better performance in large-scale particle collision system, and the contact model is the key basis for calculating the interaction force between particles, after constructing the ice particle collision model, various parameters in the ice particle collision process are obtained, including contact radius, normal contact force, tangential force and tangential damping force, etc.

[0038] In addition, the DEM includes a motion control model and an erosion wear model in addition to the ice particle collision model, wherein the impact wear is caused by high-speed impact of particles in the abrasive jet on the nozzle wall, resulting in severe impact force, causing the nozzle surface material to peel off and break, and the hardness, particle size and jet speed of the abrasive affect the degree of wear, and the design and material selection of the nozzle need to consider the impact and wear resistance to improve the service life, the present application uses the Oka model to solve the wear, can quantitatively solve the particle impact wear process, and combines with the relative wear model to analyze the wear behavior of the nozzle under the action of the abrasive jet, thereby providing more comprehensive wear prediction.

[0039] Preferably, the specific steps of the step S3 are: Step S31, using the CFD model to iteratively calculate the flow field of one time step to convergence; Step S32, the DEM model starts the ice particle phase calculation, and calculates the force and motion of the ice particle according to the flow field data; Step S33, after the ice particle position is updated, the force of the ice particle on the liquid phase is added to the flow field calculation, and the steps S31-S33 are cycled to obtain the CFD-DEM coupling model; Step S34, using the conical nozzle model and the 90° elbow model to verify the flow characteristics and wear of the CFD-DEM coupling model.

[0040] The coupling process of CFD and DEM is as shown in Figure 3 The CFD and DEM are coupled to form a cycle process, after the ice particle position in the DEM is updated, the force of the ice particle on the liquid phase can be added to the flow calculation, and the CFD calculation is performed again, in the calculation process, the flow calculation of one time step is iteratively calculated to convergence, and then the DEM calculation is started again, in the DEM calculation, the force and motion of the particle are calculated according to the flow field data, and the ice particle position is updated, and the CFD-DEM coupling model is cycled to explore the flow state and wear condition.

[0041] In order to verify the reliability of the CFD-DEM coupling model, the conical nozzle model and the 90° elbow are used to verify the flow characteristics and wear model, and the reliability and accuracy of the CFD-DEM coupling model in the calculation of the post-mixed abrasive water jet are verified.

[0042] Preferably, the specific steps of the step S4 are: A post-mixed abrasive jet nozzle physical model is constructed, the post-mixed abrasive jet nozzle physical model comprises a high-pressure water pipeline, a mixing chamber, a contraction transition section and a focusing pipe connected in sequence, and a feeding pipe is arranged on the mixing chamber; LBM model is constructed by using lattice Boltzmann method, the minimum velocity of ice particle at the outlet of the physical model of the post-mixed abrasive jet nozzle and the time-averaged velocity at the outlet of the flow field are selected as the boundary conditions of the LBM model, the LBM model is simplified as a uniform heat flow field, and the ice particle is fixed at the center of the flow field; Through dimensionless processing, the velocity field, temperature field and volume fraction cloud chart around the ice particle under different Reynolds numbers are calculated by using the LBM model for analysis, and the verified CFD-DEM coupling model is simplified based on the analysis results.

[0043] After the verification of the CFD-DEM coupling model is completed, the CFD-DEM numerical simulation can be carried out by using the post-mixed abrasive jet nozzle physical model in Figure 4 , the data calculated are used to construct the LBM model to study the phase change process of the ice particle, in order to accurately simulate the heat exchange process between the ice particle and the fluid and capture the phase change behavior of the ice particle, the LBM model is constructed by using the lattice Boltzmann method, and the minimum velocity of the ice particle at the outlet of the post-mixed abrasive jet nozzle physical model and the time-averaged velocity at the outlet of the flow field are selected as the boundary conditions, at the same time, the ice particle phase change model is simplified: the LBM flow field model is simplified as a uniform heat flow field, and the ice particle is fixed at the center of the flow field, the temperature value of the uniform heat flow field is provided by the CFD-DEM calculation result, the velocity field, temperature field and volume fraction cloud chart around the ice particle under different Reynolds numbers are calculated by using the LBM model, and the variation law of the ice particle volume with dimensionless time is analyzed to study the melting characteristics of the ice particle.

[0044] As shown in Figure 5 , the velocity field distribution under four Reynolds numbers is shown, with the increase of Reynolds number, the velocity distribution presents the following regular variation: on the windward surface of the fluid impacting the ice particle, the fluid velocity gradually decreases, forming a low-speed zone, and the stagnation flow phenomenon appears, the range of the stagnation flow zone gradually expands, the fluid is more obviously hindered by the ice particle, and the degree of velocity reduction is also more obvious, more kinetic energy is converted into other forms of energy or momentum, on both sides of the ice particle, due to the need for the fluid to bypass the fixed ice particle, the flow channel becomes narrow, according to Bernoulli principle, the fluid flow rate will increase, according to Figure 5 , it can be seen that the velocity field on the upper and lower sides of the ice particle is greater than the given dimensionless velocity, the wake zone is a low-speed area formed due to the separation of the fluid after bypassing the ice particle, with the increase of Reynolds number, the length of the wake zone increases obviously, and becomes more elongated, at the same time, the velocity gradient in the wake zone is also larger, the velocity changes more sharply, and the flow is more unstable, according to fluid mechanics, the greater the Reynolds number, the stronger the inertial force of the flow, the longer the wake, and the more likely to lose stability to form a vortex.

[0045] As shown in Figure 6The figure shows the dimensionless temperature distribution cloud around the ice particle. At the leading edge of the ice particle, when the fluid impacts the front surface of the ice particle, its velocity decreases or even approaches zero. During this process, the fluid's kinetic energy is partially converted into internal energy, resulting in a local temperature slightly higher than the fluid temperature. As the Reynolds number increases, the area of ​​elevated temperature increases, but the magnitude of the temperature increase is not significant, so the impact of changes in the Reynolds number on this area is relatively small. The most significant temperature change occurs behind the ice particle. When the Reynolds number is low, a distinct cold tail region forms behind the ice particle. At this point, the ice particle undergoes a phase change, absorbing surrounding heat and causing the temperature to drop. As the Reynolds number increases, the length of the cold tail region gradually increases, while its width decreases. As the temperature rises, the heat transfer efficiency in the wake region increases, allowing the fluid to remove heat more quickly, allowing the wake region to return to ambient temperature more quickly. Symmetrical cold regions gradually emerge on both sides of the ice particle as the Reynolds number increases, and the extent and intensity of these cold regions also increase with increasing Reynolds number. This is because the fluid flowing around the ice particles forms local eddies on both sides, which enhances convective heat transfer and causes the local temperature to drop. The intensity of the eddies increases with the increase in speed, so the low-temperature areas on both sides become more obvious.

[0046] like Figure 7 As shown in the figure, the volume of the ice particles hardly changes significantly with increasing Reynolds number. The ice particles always maintain a relatively complete round shape, indicating that within the simulated Reynolds number range, changes in flow rate have little effect on the melting or volume change of the ice particles, and the degree of phase change of the ice particles can be ignored.

[0047] Since it is difficult to visually observe the change of ice particle volume in the ice particle volume cloud diagram, the curve of ice particle volume fraction changing with time at different Reynolds numbers is drawn, such as Figure 8 As shown in the figure, the overall trend shows that the volume fraction curves under all operating conditions show a decreasing trend, and the rate of volume decrease slightly accelerates with increasing Reynolds number. At lower Reynolds numbers, the volume fraction decreases relatively slowly, remaining above 97.5% at t*=26. However, the melting of ice particles does not follow a linear relationship. As can be seen from the figure, before time t*=15, all operating conditions approach a linear downward trend. However, after t*=15, the downward trend of the curves for the operating conditions of Re=10.8 and 14.4 begins to accelerate, exceeding that of the operating conditions of Re=18 and 23.4. Combined with the analysis of the temperature field cloud map, it can be seen that before t*=15, the temperature difference around the ice particles at different Reynolds numbers is not large, so the difference in the melting rate of the ice particles is relatively small.

[0048] With the melting process, the cooling effect of the wake region of the fluid with larger Reynolds number is weakened, and more heat is taken away instead of continuously transferred to the ice particles. At the same time, the low-temperature region on both sides is more obvious, and the local convective heat transfer is enhanced, but the heat in these regions is not effectively transferred to the ice particles, but instead slows down the phase change speed of the ice particles. For the working condition with smaller Reynolds number, the wake region is relatively simple, which is more conducive to the continuous transfer of heat to the surface of the ice particles, so that the ice particles melt at a low speed.

[0049] After t*=15, the heat transfer efficiency of the wake region of the working condition with larger Reynolds number decreases instead, and the local cooling effect on both sides further limits the heat transfer to the center of the ice particles. At the same time, due to the faster initial melting of the ice particles under the working condition with larger Reynolds number, the heat transfer area is reduced, further limiting the efficiency of heat transfer. For the ice particles with smaller Reynolds number, due to the slower early melting and the higher temperature of the front end of the ice particles, the surface area of the ice particles becomes larger after melting, plus the relatively simple wake structure, which is more conducive to the continuous transfer of heat, thus leading to the volume reduction speed of the ice particles exceeding that of the working condition with larger Reynolds number.

[0050] For a large Reynolds number of more than 100, the volume fraction of the ice particles decreases faster, and decreases to about 96% at t*=26. Under the same time scale, the melting amount under the high Reynolds number condition is larger than that under the low Reynolds number, indicating that the melting rate under the high Reynolds number condition is faster. At this time, convective heat transfer dominates heat transfer, which increases the temperature gradient around the ice particles, thereby increasing the melting rate.

[0051] Figure 9 The percentage of ice particle volume loss under different Reynolds numbers is shown, that is, the proportion of the melted part of the ice particles. It can be found that the volume loss percentage changes little as the Reynolds number increases from 10.8 to 23.4; and under the large Reynolds number working condition, the volume loss percentage starts to increase again, and reaches a maximum of about 4% at Re=201. Although the influence of Reynolds number on melting shows non-monotonicity in the studied Reynolds number range, the melting proportion is less than 10%, and the phase change degree of the ice particles is low, so the phase change of the ice particles is ignored in the subsequent ice particle abrasive jet research, thereby simplifying the calculation model.

[0052] Preferably, the dimensionless processing includes dimensionless processing of velocity, temperature, length and time, specifically: 、 、 、 ; wherein, 、 、 、 are dimensionless velocity, temperature, length and time, respectively; 、 , actual velocity, temperature and length, respectively; characteristic velocity and temperature; D is the ice particle diameter; N is the calculation time step, and d is the number of lattices occupied by the ice particles.

[0053] Non-dimensionalization is an indispensable key step in the lattice Boltzmann method, which fundamentally eliminates the influence of artificially set unit systems on numerical calculation results, and improves the efficiency, stability and universality of the calculation.

[0054] Preferably, the specific step of performing flow state analysis of the solid two-phase flow in the step S5 is: determining the variables as the length-diameter ratio of the mixing chamber, the abrasive incidence angle, the abrasive particle size and the abrasive mass flow rate; determining the affected factors as the nozzle flow field and pressure distribution, the abrasive mass concentration distribution, the abrasive spatial position distribution and the abrasive velocity distribution; adopting the control variable method to compare and analyze the influence of different variables on the affected factors through the CFD-DEM coupling model, and obtain the flow state analysis results.

[0055] The length-diameter ratio of the nozzle mixing chamber is one of the key geometric parameters affecting the flow characteristics of the jet. The change of the length-diameter ratio will directly affect the flow field structure and energy conversion efficiency inside the nozzle, and then have a significant impact on the processing performance of the jet. The change of the abrasive incidence angle will directly affect the interaction mode between the abrasive particles and the high-pressure water jet, the energy transfer efficiency and the distribution state of the abrasive particles inside the nozzle. The abrasive particle size directly affects the momentum exchange between the abrasive particles and the high-pressure water jet, the energy transfer efficiency and the transport characteristics of the abrasive particles inside the nozzle. The change of the abrasive mass flow rate will directly affect the energy exchange strength between the abrasive particles and the high-pressure water jet, the energy transport efficiency of the jet and the abrasive concentration distribution inside the nozzle. The length-diameter ratio of the mixing chamber, the abrasive incidence angle, the abrasive particle size and the mass flow rate in the abrasive jet system are simulated and calculated, and the influence of these variables on the flow field velocity and pressure distribution, the abrasive concentration and spatial position distribution and the abrasive velocity distribution in the nozzle is compared and analyzed, and the following conclusions are obtained: (1) With the increase of the length-diameter ratio, the following rules are presented: ① flow field velocity and pressure: the jet core area shrinks, and the pressure in the mixing chamber first decreases and then increases. ② abrasive mass concentration: when the length-diameter ratio is 1.6 and 2.4, a high concentration area appears at the front end of the mixing chamber; when the length-diameter ratio is 1.8 and 2, the high concentration area decreases. ③ abrasive spatial position distribution: after the increase of the length-diameter ratio, the abrasive distribution is concentrated, and the focusing effect is improved; when the length-diameter ratio is 2.4, the focusing effect is improved limitedly. ④ abrasive velocity distribution: the tangential velocity of the abrasive in the second half of the focusing tube increases with the increase of the length-diameter ratio; the velocity in region A is constant, and the velocity in regions B and C slightly decreases and the fluctuation decreases. When the length-diameter ratio is 1.6, the proportion of the abrasive particles with a residence time less than 0.02 s in the nozzle is the largest, which is 85.14%. ​

[0056] (2) With the decrease of the incident angle, the following rules are presented: ① Flow field velocity and pressure: the core area of the jet gradually disperses, and the pressure of the mixing chamber continuously increases. ② Abrasive mass concentration: the high concentration area gradually spreads and the distribution range expands. ③ Spatial distribution of abrasives: the accumulation of abrasives at the top first increases and then decreases, and the distribution of abrasives is more uniform, which is more conducive to the ejection of abrasives. ④ Abrasive velocity distribution: the tangential velocity of abrasives in the second half of the focusing tube first decreases and then increases; the velocity is constant in region A, and the velocity slightly decreases and the fluctuation decreases in regions B and C. The proportion of short residence time of abrasives decreases with the decrease of the incident angle.

[0057] (3) With the increase of the particle size, the following rules are presented: ① Flow field velocity and pressure: the core area of the jet gradually expands, and the pressure of the mixing chamber remains unchanged. ② Abrasive mass concentration: when the particle size is small, the abrasive mass concentration is relatively uniform, and when the particle size becomes large, the concentration is locally concentrated at the front end. ③ Spatial distribution of abrasives: the cross-section presents the phenomenon of sparse in the middle and accumulation on the circumference, except for the working condition of particle size 100 μm, the distribution of other abrasives is concentrated. ④ Abrasive velocity distribution: the velocity of abrasives in region A decreases, and the velocity fluctuation in regions B and C weakens. The proportion of short residence time of abrasives first increases, then decreases, and then increases, and it is the largest when dp=100 μm, which is 83.28%.

[0058] (4) With the increase of the mass flow rate, the following rules are presented: ① Flow field velocity and pressure: the core area of the jet shrinks, and the pressure of the mixing chamber remains unchanged. ② Abrasive mass concentration: the area of the high concentration region expands and extends downstream. ③ Spatial distribution of abrasives: the distribution is uniform when the mass flow rate is small, and it converges into a group when the mass flow rate is large; with the increase of the flow rate, the accumulation at the top intensifies, but the focusing property in the downstream region is better. ④ Abrasive velocity distribution: the tangential velocity of abrasives in the second half of the focusing tube decreases slightly; the velocity fluctuation in regions B and C first weakens and then enhances. The proportion of short residence time of abrasives first increases and then decreases, and it is the largest when Qm=0.3 g / s, which is 85.54%.

[0059] Preferably, the specific steps of the step S5 of performing wear analysis of the nozzle are: determining the variables as the length-diameter ratio of the mixing chamber, the incident angle of the abrasives, the particle size of the abrasives, and the mass flow rate of the abrasives; determining the affected factors as the normal and tangential cumulative energy and the Oka wear distribution; adopting the control variable method to compare and analyze the influence of different variables on the affected factors through the CFD-DEM coupling model, and obtain the wear analysis results.

[0060] Nozzle, as the core component of the jet system, its wear characteristics directly determine the processing efficiency and equipment maintenance cost. Under the continuous impact of high-speed ice particles, the nozzle material will gradually fail due to erosion wear, resulting in the decline of jet focusing performance and the increase of energy consumption. The normal and tangential cumulative energy of the nozzle can be used as an important indicator to measure the wear of the component. The greater the cumulative energy on the wall surface, the more likely it is to occur wear behavior, and the more severe the wear will be. By comparing and analyzing the influence of the length-diameter ratio of the mixing chamber, the abrasive incidence angle, the abrasive particle size and mass flow rate on the normal and tangential cumulative energy of the nozzle wall and the Oka wear distribution in the abrasive jet system, the following conclusions are drawn: (1) With the increase of the length-diameter ratio, the high value region of the normal cumulative energy gradually extends upstream, and the distribution range of the energy concentration region in the contraction section decreases. With the increase of the length-diameter ratio from 1.6 to 2, the tangential cumulative energy distribution in the contraction section decreases; when the length-diameter ratio increases to 2.4, the tangential energy in the mixing chamber increases significantly, and the energy intensity increases. In the focusing tube section, the normal and tangential cumulative energy is concentrated in the entrance section, and the cumulative energy is the smallest when the length-diameter ratio is 2 and the largest when the length-diameter ratio is 2.4. The Oka wear area in the whole nozzle first decreases and then increases, and the wear is the most serious when the length-diameter ratio is 2.4, which is concentrated in the front end of the mixing chamber and the entrance section of the focusing tube.

[0061] (2) With the decrease of the incidence angle, the distribution area of the normal and tangential cumulative energy remains basically unchanged as the incidence angle decreases, but when the incidence angle is 45°, the cumulative energy range and intensity in the mixing chamber and the contraction section are greatly improved. In the focusing tube section, the normal and tangential cumulative energy is concentrated in the entrance section, and the range first increases and then decreases, and the cumulative energy is the largest when the incidence angle is 45° and the distribution extends downstream. The Oka wear changes little with the incidence angle, and the severe wear area is concentrated in the connection between the mixing chamber and the contraction section, and the connection between the contraction section and the focusing tube. When the incidence angle is 45°, the wear is relatively serious, which is concentrated in the front end of the mixing chamber and the entrance section of the focusing tube.

[0062] (3) With the increase of the abrasive particle size, the distribution area and energy intensity of the normal and tangential cumulative energy gradually increase, and the tangential energy accumulation is significantly greater than the normal accumulation. In the focusing tube section, the normal and tangential cumulative energy range first decreases and then increases, and is concentrated in the entrance section, and is relatively small when the particle size is 110 μm. With the increase of the particle size, the Oka wear gradually expands in the severe wear area of the contraction section, the top of the mixing chamber and the first half of the focusing tube, while the moderate wear area in the chamber gradually shrinks and concentrates upstream.

[0063] (4) With the increase of mass flow rate, the distribution area and energy intensity of normal and tangential cumulative energy gradually expand, and the tangential cumulative energy is significantly higher than the normal cumulative energy. In the focusing tube section, the normal and tangential cumulative energy is mostly concentrated in the front half, and the energy peak area gradually increases. With the increase of mass flow rate from 0.2 g / s to 0.35 g / s, the Oka wear gradually expands in the severe wear area at the top of the contraction section and the mixing chamber, and the moderate wear area in the chamber gradually extends downstream. In terms of wear quantification, the greater the mass flow rate, the more serious the wear.

[0064] Preferably, the length-diameter ratio of the mixing chamber of the nozzle, the abrasive incidence angle, the abrasive particle size and the abrasive mass flow rate are optimized according to the flow state analysis results and the wear analysis results.

[0065] Finally, the four variables are adjusted based on the flow state analysis results and the wear analysis results, thereby providing theoretical support for optimizing the jet process and the nozzle design.

[0066] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A post-mixed ice abrasive jet nozzle optimization method, characterized in that: This includes the following methods: Step S1: obtaining basic parameters of the nozzle to be optimized and constructing a CFD model for the continuous phase; Step S2: establishing an ice particle database, and establishing a DEM model for the discrete phase based on the data in the ice particle database; Step S3: Coupling the CFD model and the DEM model to obtain a CFD-DEM coupling model, and verifying the CFD-DEM coupling model; Step S4: constructing an ice particle phase change model using the lattice Boltzmann method to simulate heat transfer characteristics, and simplifying the verified CFD-DEM coupling model based on the ice particle phase change model; Step S5: performing flow pattern analysis of solid two-phase flow and nozzle wear analysis based on the simplified CFD-DEM coupling model; Step S6: Optimizing the nozzle according to the flow pattern analysis results and the wear analysis results; The specific steps of step S4 are: Constructing a physical model of a post-mixed abrasive jet nozzle, the physical model of the post-mixed abrasive jet nozzle includes a high-pressure water pipe, a mixing chamber, a contraction transition section, and a focusing tube connected in sequence, wherein a feed pipe is provided on the mixing chamber; The LBM model was constructed using the lattice Boltzmann method. The minimum velocity of ice particles at the outlet of the post-mixed abrasive jet nozzle physical model and the time-averaged velocity at the outlet of the flow field were selected as the boundary conditions of the LBM model. The LBM model was simplified to a uniform thermal flow field, and the ice particles were fixed at the center of the flow field. Through dimensionless processing, the LBM model is used to calculate the velocity field, temperature field and volume fraction cloud map around the ice particles under different Reynolds numbers. Based on the analysis results, the verified CFD-DEM coupling model is simplified.

2. The method for optimizing a post-mixed ice abrasive jet nozzle according to claim 1, wherein: The specific steps of step S1 are: Obtaining the inlet end parameters, internal channel parameters and outlet end parameters of the nozzle to be optimized as basic parameters; Construct the continuity equation based on the basic parameters: The initial continuity equation is constructed as: ,in 、 、 represent the velocity components of the fluid, is the fluid density, For time, 、 、 are the three coordinate axes of the spatial rectangular coordinate system; Bring in Operator: , , 、 、 are the unit vectors in the positive directions of the x-axis, y-axis, and z-axis, respectively. is the velocity vector of the fluid. When calculating incompressible flow, the fluid density is a constant, the initial continuity equation becomes: ; Construct the momentum conservation equation based on basic parameters: Based on the principle of conservation of momentum, the momentum conservation equations in the X, Y, and Z directions are derived: ； ； ； in Indicates static pressure, express External force in the direction, represents the stress tensor; Construct the energy conservation equation based on basic parameters: , where T is the temperature, is the heat transfer coefficient, It is the part that contains the internal heat source of the fluid and the part that converts mechanical energy into thermal energy. is the divergence operator, is the temperature gradient, is the constant pressure specific heat capacity of the fluid; use The model builds a turbulence model based on basic parameters: ； ； The effective viscosity , Indicates molecular viscosity, turbulent viscosity , is the fluid density, is the turbulent kinetic energy dissipation rate, represents the turbulent kinetic energy, is a dimensionless empirical constant, is the turbulent energy term caused by velocity difference and buoyancy, and Represent k and The Prandtl number, reflects the effect of turbulence on the total dissipation rate, 、 、 is an empirical constant, and R is the correction of the dissipation term caused by Reynolds stress.

3. The method for optimizing a post-mixed ice abrasive jet nozzle according to claim 1, wherein: The specific steps of step S2 are: Create an ice particle collision model that includes the mass, damping coefficient, and elastic coefficient of the ice particles: ,in 、 is the mass and displacement of the oscillator, c, are the damping coefficient and elastic coefficient, are relative acceleration and relative velocity respectively; When the ice particles collide, the normal overlap is: ,in and is the vector position of the sphere's center, and are the radii of particles i and j respectively; The contact radius between ice particles is: , ; The normal contact force between ice particles is , ,in , are the elastic moduli of ice particles i and j, 、 are the Poisson's ratios of ice particles i and j, respectively; The normal damping force is: , ,in , the expression is: are the masses of particle i and particle j respectively, is the relative normal velocity of ice particles i and j: , The velocity vectors of particles 1 and 2, and n is the normal unit vector when the ice particles collide: , and are the vector positions of the sphere center; Tangential force between ice particles for: ,in is the tangential overlap, is the tangential stiffness: , where G* is the equivalent shear modulus: In the formula 、 are the shear moduli of material i and material j respectively; The tangential damping force after ice particle collision is: Establish the motion control equation of ice particles: ， ， ； The resistance force on the ice particles is ; is the relaxation time; is the particle size; 、 is the velocity of the fluid and ice particles; are the density of ice particles and the viscosity of the fluid respectively; is the ice particle Reynolds number, is the drag coefficient, and are respectively the acceleration due to gravity and other forces acting on the particles except the drag force and buoyancy-gravity force. For spherical ice particles, the drag coefficient is calculated by the following formula: The Oka model is used to establish the erosion wear model: in 、 are the nozzle surface material hardness and wall area respectively; 、 is the ice particle velocity and diameter; Wear caused by any impact angle; 、 are the velocity and diameter of the reference ice particle; g(α) is the function of the impact angle α; is the mass flow rate; K, a, b, k1, k2, k3, n1, n2 are constants.

4. The method for optimizing a post-mixed ice abrasive jet nozzle according to claim 1, wherein: The specific steps of step S3 are: Step S31, using the CFD model to iterate the flow field calculation for one time step until convergence; Step S32: The DEM model starts calculating the ice particle phase and calculates the forces and motions of the ice particles based on the flow field data. Step S33: After the ice particle position is updated, the force exerted by the ice particles on the liquid phase is added to the flow field calculation, and steps S31-S33 are repeated to obtain a CFD-DEM coupling model; Step S34: Use the tapered nozzle model and the 90° elbow model to perform flow characteristic verification and wear verification on the CFD-DEM coupling model respectively.

5. The method for optimizing a post-mixed ice abrasive jet nozzle according to claim 1, wherein: The dimensionless processing includes dimensionless processing of speed, temperature, length and time, specifically: 、 、 、 ； in, 、 、 、 are dimensionless velocity, temperature, length, and time; 、 、 are actual speed, temperature and length respectively; 、 are the characteristic velocity and characteristic temperature; D is the ice particle size; N is the calculation time step, and d is the number of grids occupied by ice particles.

6. The method for optimizing a post-mixed ice abrasive jet nozzle according to claim 1, characterized in that: The specific steps of performing flow pattern analysis of solid two-phase flow in step S5 are as follows: The variables determined are the aspect ratio of the mixing chamber, the abrasive incident angle, the abrasive particle size and the abrasive mass flow rate; The influencing factors are determined to be the nozzle flow field and pressure distribution, abrasive mass concentration distribution, abrasive spatial position distribution, and abrasive velocity distribution; The control variable method is used to compare and analyze the effects of different variables on the affected factors through the CFD-DEM coupling model to obtain the flow pattern analysis results.

7. The method for optimizing a post-mixed ice abrasive jet nozzle according to claim 6, characterized in that: The specific steps of performing nozzle wear analysis in step S5 are as follows: The variables determined are the aspect ratio of the mixing chamber, the abrasive incident angle, the abrasive particle size and the abrasive mass flow rate; The influencing factors were determined to be normal and tangential accumulated energy and Oka wear distribution; The control variable method is used to compare and analyze the effects of different variables on the affected factors through the CFD-DEM coupling model to obtain the wear analysis results.

8. The method for optimizing a post-mixed ice abrasive jet nozzle according to claim 7, wherein: According to the flow pattern analysis results and wear analysis results, the mixing chamber aspect ratio of the nozzle, the abrasive incident angle, the abrasive particle size and the abrasive mass flow rate are optimized.

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