A method of optimizing a post-mix ice abrasive jet nozzle

Abstract

The application discloses an optimization method of a post-mixing ice abrasive jet nozzle, and steps are as follows: obtaining basic parameters of a nozzle to be optimized, and constructing a CFD model for a continuous phase; establishing an ice particle database, and establishing a DEM model for a discrete phase based on data in the ice particle database; coupling based on the CFD model and the DEM model, obtaining a CFD-DEM coupling model, and verifying the CFD-DEM coupling model; constructing an ice particle phase change model by using a lattice Boltzmann method to simulate heat exchange characteristics, simplifying the CFD-DEM coupling model after verification based on the ice particle phase change model; performing flow state analysis of solid two-phase flow and wear analysis of the nozzle based on the simplified CFD-DEM coupling model; and optimizing the nozzle according to the flow state analysis result and the wear analysis result, so as to provide theoretical support for optimizing jet process and nozzle design. Meanwhile, the lattice Boltzmann method is introduced to establish the ice particle phase change model, the rationality of the ice particle phase change model is verified through numerical simulation, the CFD-DEM coupling model is simplified while ensuring calculation precision, and 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 in 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 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 high concentration of jet and stable processing process, and can obtain good surface quality. However, the pre-mixed abrasive jet has the disadvantages of short service life due to the easy wear of the high-pressure pipeline and nozzle. The post-mixed abrasive jet has the advantages of simple structure, low cost, easy maintenance and less wear of the high-pressure water pipe, and is widely used.

[0003] In order to avoid pollution to the marine environment, the ice abrasive jet technology replaces traditional abrasives such as sand and steel balls with ice particles as natural low-temperature abrasives. The 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 precision. 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:

[0006] A post-mixing ice abrasive jet nozzle optimization method, comprising the following methods:

[0007] Step S1, obtaining the basic parameters of the nozzle to be optimized, and constructing a CFD model for the continuous phase;

[0008] 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;

[0009] 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;

[0010] 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;

[0011] 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;

[0012] Step S6, optimizing the nozzle according to the flow state analysis result and the wear analysis result.

[0013] Preferably, the specific steps of step S1 are as follows:

[0014] Obtaining the inlet end parameters, internal channel parameters and outlet end parameters of the nozzle to be optimized as the basic parameters;

[0015] Constructing a continuity equation based on the basic parameters:

[0016] The initial continuity equation is constructed as: wherein , , respectively represent the velocity components of the fluid, is the fluid density, is time, , , are three coordinate axes of a spatial rectangular coordinate system;

[0017] Substituting operator: , , , , respectively are the unit vectors of the positive direction of the x-axis, the y-axis and the z-axis, is the velocity vector of the fluid, when calculating the incompressible flow, the fluid density is a constant, and the initial continuity equation becomes: ;

[0018] Constructing a momentum conservation equation based on the basic parameters:

[0019] Based on the principle of momentum conservation, the momentum conservation equations in X, Y and Z directions are derived:

[0020] ;

[0021] ;

[0022] ;

[0023] wherein p represents static pressure, F represents external force in the X direction, σ represents stress tensor; Based on the basic parameters, the energy conservation equation is constructed: wherein T represents temperature,

[0024] h represents heat transfer coefficient, Q represents internal heat source of the fluid and the part of mechanical energy converted into heat energy, ∇ represents divergence operator, ∇T represents temperature gradient, cp represents constant pressure specific heat capacity of the fluid; The turbulence model is constructed based on the basic parameters by using the model:

[0025]

[0026] ;

[0027] ;

[0028] wherein effective viscosity , μ represents molecular viscosity, turbulent viscosity , ρ represents fluid density, ε represents turbulent kinetic energy dissipation rate, k represents turbulent kinetic energy, C represents dimensionless empirical constant, G represents turbulent energy item caused by velocity difference and buoyancy, and respectively represent Prandtl number of k and , reflects the influence of turbulence on total dissipation rate, , , is an empirical constant, and R represents correction of dissipation item caused by Reynolds stress.

[0029] Preferably, the specific steps of the step S2 are as follows:

[0030] ​​A model for ice particle collisions is established, which includes ice particle mass, damping coefficient and elastic coefficient: 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;

[0031] When 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;

[0032] The contact radius between ice particles is: , ;

[0033] The normal contact force between ice particles is , where , are the elastic moduli of ice particles i and j, respectively, , are the Poisson's ratios of ice particles i and j, respectively;

[0034] The normal damping force is: , where , the expression is:

[0035]

[0036] 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 particle 1 and particle 2, n is the normal unit vector when ice particles collide: , and are the vector positions of the sphere centers;

[0037] The tangential force between ice particles is: where is the tangential overlap, is the tangential stiffness: where G* is the equivalent shear modulus:

[0038]

[0039] In the formula , Let be the shear moduli of material i and material j, respectively;

[0040] The tangential damping force after the collision of ice particles is:

[0041]

[0042] Establish the governing equations for the motion of ice particles:

[0043] , , ;

[0044] in Let be the acceleration of the t-th particle in the x-direction, and let be the drag force experienced by the ice particle. ; This refers to the relaxation time; Particle size; , The velocity of the fluid and ice particles; These represent the density of the ice particles and the viscosity of the fluid, respectively. For ice particles, Reynolds number The drag coefficient, and These are the gravitational acceleration and the other forces acting on the particle besides drag and buoyancy-gravity, respectively. For spherical ice particles, the drag coefficient is calculated using the following formula:

[0045]

[0046] An erosion wear model was established using the Oka model:

[0047]

[0048]

[0049]

[0050]

[0051] in , These are the hardness of the nozzle surface material and the wall area, respectively. , For ice particle velocity and diameter; Wear caused by any impact angle; , The velocity and diameter of the reference ice particle are given; g(α) is a function of the impact angle α; Let K be the mass flow rate; K, a, b, k1, k2, k3, n1, n2 are constants.

[0052] Preferably, the specific steps of step S3 are as follows:

[0053] Step S31, the flow field of one time step is calculated iteratively to convergence by using the CFD model;

[0054] Step S32, the DEM model starts the calculation of ice particle phase, and the force and movement of ice particle are calculated according to the flow field data;

[0055] Step S33, after the position of ice particle is updated, the force of ice particle on liquid phase is added to the flow field calculation, and steps S31-S33 are cycled to obtain the CFD-DEM coupling model;

[0056] Step S34, the flow characteristic verification and the wear verification of the CFD-DEM coupling model are carried out by using the conical nozzle model and the 90° elbow model respectively.

[0057] Preferably, the specific steps of step S4 are as follows:

[0058] 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 cavity, a contraction transition section and a focusing tube connected in sequence, and a feeding pipe is arranged on the mixing cavity;

[0059] An LBM model is constructed by using the lattice Boltzmann method, the minimum speed of ice particle at the outlet of the physical model of the post-mixed abrasive jet nozzle and the time-averaged speed 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 in the center of the flow field;

[0060] Through dimensionless processing, the velocity field, temperature field and volume fraction cloud chart of ice particle around at different Reynolds numbers are calculated and analyzed by using the LBM model, and the CFD-DEM coupling model verified is simplified based on the analysis results.

[0061] Preferably, the dimensionless processing includes dimensionless processing of velocity, temperature, length and time, and specifically:

[0062] 、 、 、 ;

[0063] Wherein, 、 、 are the dimensionless velocity, temperature, length and time respectively; 、 、 are the actual velocity, temperature and length respectively; 、 ​wherein, V is the characteristic velocity and T is the characteristic temperature; D is the ice particle diameter; N is the calculation time step, and d is the number of lattices occupied by the ice particle.

[0064] Preferably, the step S5 comprises the following specific steps of solid two-phase flow state analysis:

[0065] The determined variables are the length-diameter ratio of the mixing chamber, the abrasive incidence angle, the abrasive particle size, and the abrasive mass flow rate.

[0066] The determined affected factors are the nozzle flow field and pressure distribution, the abrasive mass concentration distribution, the abrasive spatial position distribution, and the abrasive velocity distribution.

[0067] The control variable method is adopted to compare and analyze the influence of different variables on the affected factors through the CFD-DEM coupling model, so as to obtain the flow state analysis result.

[0068] Preferably, the step S5 comprises the following specific steps of nozzle wear analysis:

[0069] The determined variables are the length-diameter ratio of the mixing chamber, the abrasive incidence angle, the abrasive particle size, and the abrasive mass flow rate.

[0070] The determined affected factors are the normal and tangential cumulative energy and the Oka wear distribution.

[0071] The control variable method is adopted to compare and analyze the influence of different variables on the affected factors through the CFD-DEM coupling model, so as to obtain the wear analysis result.

[0072] Preferably, the length-diameter ratio of the mixing chamber, the abrasive incidence angle, the abrasive particle size, and the abrasive mass flow rate of the nozzle are optimized according to the flow state analysis result and the wear analysis result.

[0073] Compared with the prior art, the present application has the following beneficial effects:

[0074] The present application is a kind of post-mixed ice abrasive jet nozzle optimization method, which is used for the optimization of post-mixed abrasive nozzle using ice abrasive. After simulating the continuous phase and the discrete phase of the nozzle, CFD model and DEM model can be respectively constructed. Then, CFD model and DEM model are combined to obtain CFD-DEM coupling model. Considering that the phase change of ice particles will increase the complexity of numerical simulation, lattice Boltzmann method is introduced to construct ice particle phase change model. The influence degree of the phase change effect of ice particles on the overall model is verified through the ice particle phase change model, so as to simplify the subsequent calculation of CFD-DEM coupling model and ensure the feasibility of numerical calculation. Finally, through CFD-DEM coupling model, flow state analysis of solid two-phase flow and wear analysis of nozzle are carried out. The nozzle can be optimized according to the analysis result, so as to optimize the jet process and prolong the service life of the jet nozzle. BRIEF DESCRIPTION OF DRAWINGS

[0075] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed to be used in the embodiments will be briefly introduced as follows. Obviously, the drawings in the following description only are the preferred embodiments of the present application, and for those skilled in the art, other drawings can also be obtained from these drawings without any creative effort.

[0076] Figure 1 A flow chart of a post-mixing ice abrasive jet nozzle optimization method of the present application;

[0077] Figure 2 A main technical route map of a post-mixing ice abrasive jet nozzle optimization method of the present application;

[0078] Figure 3 A coupling schematic diagram of a CFD model and a DEM model of a post-mixing ice abrasive jet nozzle optimization method of the present application;

[0079] Figure 4 A physical model schematic diagram of a post-mixing abrasive jet nozzle of a post-mixing ice abrasive jet nozzle optimization method of the present application;

[0080] Figure 5 A velocity distribution nephogram calculated by using an LBM model in a post-mixing ice abrasive jet nozzle optimization method of the present application under different Reynolds numbers;

[0081] Figure 6 A temperature distribution nephogram calculated by using an LBM model in a post-mixing ice abrasive jet nozzle optimization method of the present application under different Reynolds numbers;

[0082] Figure 7 An ice particle volume nephogram calculated by using an LBM model in a post-mixing ice abrasive jet nozzle optimization method of the present application under different Reynolds numbers;

[0083] Figure 8 A curve of ice particle volume fraction changing with time under different Reynolds numbers;

[0084] Figure 9 An ice particle melting volume fraction diagram under different Reynolds numbers; DETAILED DESCRIPTION

[0085] In order to better understand the technical content of the present application, a specific embodiment will be provided below, and the present application will be further described in combination with the drawings.

[0086] Referring to Figures 1 to 2 The post-mixing ice abrasive jet nozzle optimization method provided by the present application comprises the following methods:

[0087] Step S1, obtain the basic parameters of the nozzle to be optimized, and construct a CFD model for the continuous phase;

[0088] Step S2, establish an ice particle database, and establish a DEM model for the discrete phase based on the data in the ice particle database;

[0089] 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;

[0090] Step S4, using the lattice Boltzmann method to construct an ice particle phase change model to simulate the heat transfer characteristics, and simplifying the CFD-DEM coupling model based on the ice particle phase change model;

[0091] Step S5, based on the simplified CFD-DEM coupling model, analyzing the flow state of the solid two-phase flow and the wear of the nozzle;

[0092] Step S6, optimizing the nozzle according to the flow state analysis result and the wear analysis result.

[0093] The application is applied to a post-mixed abrasive jet nozzle with ice particles as abrasive, in order to further optimize the nozzle, the flow state of the solid two-phase flow of the ice abrasive in the jet nozzle and the wear condition are analyzed, so that the nozzle design process and structure are optimized, and the service life of the nozzle is prolonged, and when optimizing, first, a CFD model for the continuous phase is constructed according to the basic parameters of the nozzle to be optimized, wherein the continuous phase is a fluid containing a single liquid or a liquid containing a solid, and an ice particle database is constructed according to the ice particles as abrasive, 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, and in the abrasive jet, the change of the discrete phase will affect the continuous phase, so coupling simulation of the continuous phase and the discrete phase is needed, therefore, after coupling the CFD model and the DEM model, a CFD-DEM coupling model can be obtained, and the CFD-DEM coupling model is verified by using some existing physical models, the reliability of the CFD-DEM coupling model in flow state analysis and wear analysis is verified, and since the abrasive adopts ice particles, the phase change of the ice particles will significantly increase the complexity of numerical simulation, therefore, the lattice Boltzmann method is introduced to establish an ice particle phase change model, and analysis is carried out based on the ice particle phase change model, through the analysis result, it can be concluded that the ice particle phase change can be ignored, so that the subsequent calculation process of the CFD-DEM coupling model is simplified, the complexity of numerical simulation is reduced, finally, through the CFD-DEM coupling model, the flow state analysis of the solid two-phase flow and the wear analysis of the nozzle can be carried out, based on the analysis result, the preparation process and the structure of the nozzle can be optimized, the ice particle speed is improved, the screen cleaning effect is improved, the wear is reduced, and the service life of the nozzle is prolonged.

[0094] Preferably, the specific steps of step S1 are:

[0095] Obtaining the inlet end parameters, internal channel parameters and outlet end parameters of the nozzle to be optimized as basic parameters;

[0096] Constructing a continuity equation based on the basic parameters:

[0097] The initial continuity equation is constructed as: wherein , , respectively represent the velocity components of the fluid, is the fluid density, is time, , , are three coordinate axes of a spatial rectangular coordinate system;

[0098] Substituting operator: , , , , respectively are the unit vectors of the positive directions of the x-axis, y-axis and z-axis, is the velocity vector of the fluid, when calculating the incompressible flow, the fluid density is constant, and the initial continuity equation becomes: ;

[0099] Constructing a momentum conservation equation based on the basic parameters:

[0100] Based on the principle of momentum conservation, the momentum conservation equations in X, Y and Z directions are derived:

[0101] ;

[0102] ;

[0103] ;

[0104] wherein represents static pressure, represents external force in the direction, represents stress tensor;

[0105] Constructing an energy conservation equation based on the basic parameters: wherein T is temperature, is heat transfer coefficient, is the part containing the internal heat source of the fluid and the mechanical energy converted into heat energy, is divergence operator, for the temperature gradient, for the specific heat capacity of the fluid at constant pressure;

[0106] using the model constructs a turbulence model based on the basic parameters:

[0107] ;

[0108] ;

[0109] where the effective viscosity , represents the molecular viscosity, 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 a correction term for the dissipation caused by the Reynolds stress.

[0110] Preferably, the specific steps of step S2 are:

[0111] An ice particle collision model is established, which includes the mass of the ice particles, the damping coefficient and the elastic coefficient: where , is the mass and displacement of the oscillator, c, is the damping coefficient and the elastic coefficient, is the relative acceleration and the relative velocity, respectively;

[0112] 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;

[0113] The contact radius between the ice particles is: , ;

[0114] The normal contact force between the ice particles is , where , Let i and j be the elastic moduli of ice particles i and j, respectively. , Let i and j be the Poisson's ratios of ice particles i and j, respectively.

[0115] The normal damping force is: , ,in The expression is:

[0116]

[0117] Let be the masses of particle i and particle j, respectively. Let i and j be the relative normal velocities of ice particles. , The velocity vectors of particle 1 and particle 2, where n is the normal unit vector at the moment of collision of the ice particles: , and These are the vector positions of the sphere's center;

[0118] Tangential force between ice particles for: ,in This is the tangential overlap. Tangential stiffness: Where G* is the equivalent shear modulus:

[0119]

[0120] In the formula , Let be the shear moduli of material i and material j, respectively;

[0121] The tangential damping force after the collision of ice particles is:

[0122]

[0123] Establish the governing equations for the motion of ice particles:

[0124] , , ;

[0125] The resistance experienced by the ice particles is ; This refers to the relaxation time; Particle size; , The velocity of the fluid and ice particles; These represent the density of the ice particles and the viscosity of the fluid, respectively. For ice particles, Reynolds number The drag coefficient, and respectively, the other forces received by the particles except the drag force and buoyancy-gravity, the drag coefficient is calculated by the following formula for spherical ice particles:

[0126]

[0127] An erosion wear model is established by using the Oka model:

[0128]

[0129]

[0130]

[0131]

[0132] wherein , respectively, the hardness of the nozzle surface material and the wall area; , the ice particle speed and the diameter; the wear caused by an arbitrary impact angle; , the reference ice particle speed and the diameter; g (a) is a function of the impact angle a; is the mass flow rate; K, a, b, k1, k2, k3, n1, n2 are constants.

[0133] In the discrete element method, according to the contact mode, it can be divided into a hard ball model and a soft ball model, the hard ball 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 there is no significant plastic deformation of the particles during the collision, in comparison, the soft ball model is more suitable for the collision simulation of multiple particles, and it exhibits better performance in large-scale particle collision systems, and the contact model is the key basis for calculating the interaction force between particles, after the ice particle collision model is constructed, various parameters in the ice particle collision process are obtained, including the contact radius, the normal contact force, the tangential force and the tangential damping force.

[0134] In addition, the DEM includes not only the ice particle collision model, but also the motion control model and the erosion wear model, wherein the impact wear is caused by the high-speed impact of the particles in the abrasive jet on the nozzle wall, which produces a violent impact force, resulting in the stripping and cracking of the nozzle surface material, the hardness, particle size and jet speed of the abrasive and other factors will affect the degree of wear, and the design and material selection of the nozzle need to consider the impact resistance and wear resistance performance comprehensively to improve its service life, the present application solves the wear by using the Oka model, which can quantitatively solve the particle impact wear process, and combines with the relative wear model to jointly analyze the wear behavior of the nozzle under the action of the abrasive jet, so as to provide more comprehensive wear prediction.

[0135] Preferably, the specific steps of step S3 are:

[0136] Step S31, the flow field of one time step is calculated iteratively to convergence by using the CFD model;

[0137] 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;

[0138] 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 steps S31-S33 are cycled to obtain the CFD-DEM coupling model;

[0139] Step S34, the flow characteristics verification and wear verification of the CFD-DEM coupling model are carried out by using the cone nozzle model and the 90° elbow model.

[0140] 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 carried out again. In the calculation process, the flow of one time step is calculated iteratively to convergence, and then the DEM calculation is started again. In the DEM calculation, the force and movement of the particle are calculated according to the flow field data, and the ice particle position is updated. The CFD-DEM coupling model is cycled to explore the flow state and wear condition.

[0141] In order to verify the reliability of the CFD-DEM coupling model, the cone nozzle model and the 90° elbow are used to carry out the flow characteristic test and the wear model verification respectively, and the reliability and accuracy of the CFD-DEM coupling model in the calculation of the post-mixed abrasive water jet are verified.

[0142] Preferably, the specific steps of step S4 are:

[0143] 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 pipe connected in sequence, and a feed pipe is arranged on the mixing chamber;

[0144] An LBM model is constructed by using the lattice Boltzmann method, the minimum speed of the ice particle at the outlet of the post-mixed abrasive jet nozzle physical model and the time-averaged speed at the outlet of the flow field are selected as the boundary conditions of the LBM model, the LBM model is simplified to a uniform heat flow field, and the ice particle is fixed in the center of the flow field;

[0145] The velocity field, temperature field and volume fraction cloud of ice particles around the nozzle under different Reynolds numbers were calculated and analyzed by using the LBM model through dimensionless processing. Based on the analysis results, the CFD-DEM coupling model verified was simplified.

[0146] After the verification of the CFD-DEM coupling model, the CFD-DEM numerical simulation can be carried out by using the physical model of the post-mixed abrasive jet nozzle in Figure 4 The data calculated are used to construct the LBM model to study the phase change process of ice particles. In order to accurately simulate the heat exchange process between ice particles and fluid and capture the phase change behavior of ice particles, the LBM model is constructed by using the lattice Boltzmann method, and the minimum speed of ice particles at the outlet of the post-mixed abrasive jet nozzle physical model and the time-averaged speed 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 to a uniform heat flow field, and the ice particles are fixed in the flow field center. 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 around the ice particles under different Reynolds numbers are calculated by using the LBM model, and the variation law of the ice particle volume with the dimensionless time is analyzed to study the melting characteristics of the ice particles.

[0147] 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 changes: on the windward surface of the fluid impacting the ice particles, 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, and the fluid is more significantly hindered by the ice particles, 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 particles, the flow channel becomes narrow because the fluid needs to bypass the fixed ice particles. According to Bernoulli's 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 particles 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 particles. With the increase of Reynolds number, the length of the wake zone increases obviously, becoming more elongated. At the same time, the velocity gradient in the wake zone is also larger, and 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.

[0148] As shown in Figure 6The ice particle volume fraction curve under different Reynolds number is shown in FIG. 9. From the overall trend, the volume fraction curve of all working conditions presents a decreasing trend, and the volume decreases slightly faster with the increase of Reynolds number. At a small Reynolds number, the volume fraction decreases relatively slowly, and the volume fraction remains above 97.5% at t*=26. However, the melting of the ice particle is not linear. As can be seen from the figure, before t*=15, all working conditions are close to linear downward trend, but after t*=15, the curve of Re=10.8, 14.4 working conditions starts to decline faster, which exceeds the Re=18, 23.4 working conditions. Combined with the analysis of the temperature field cloud map, it can be known that before t*=15, the temperature difference around the ice particle under different Reynolds number is not large, so the melting rate of the ice particle is relatively small.

[0149] As shown in FIG. 8, with the increase of Reynolds number, the volume of the ice particle hardly changes significantly. The ice particle always maintains a relatively complete circular shape, indicating that the change of flow rate has little effect on the melting or volume change of the ice particle in the simulated Reynolds number range, and the phase change degree of the ice particle can be ignored. Figure 7

[0150] Because it is difficult to observe the change of the ice particle volume in the ice particle volume cloud map, the ice particle volume fraction curve with time under different Reynolds number is drawn, as shown in FIG. 9. From the overall trend, the volume fraction curve of all working conditions presents a decreasing trend, and the volume decreases slightly faster with the increase of Reynolds number. At a small Reynolds number, the volume fraction decreases relatively slowly, and the volume fraction remains above 97.5% at t*=26. However, the melting of the ice particle is not linear. As can be seen from the figure, before t*=15, all working conditions are close to linear downward trend, but after t*=15, the curve of Re=10.8, 14.4 working conditions starts to decline faster, which exceeds the Re=18, 23.4 working conditions. Combined with the analysis of the temperature field cloud map, it can be known that before t*=15, the temperature difference around the ice particle under different Reynolds number is not large, so the melting rate of the ice particle is relatively small. Figure 8

[0151] ​​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 being 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. The wake region of the ice particles with smaller Reynolds number 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 do not melt too slowly at low speed.

[0152] After t*=15, the heat transfer efficiency of the wake region of the ice particles with larger Reynolds number decreases, 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 with larger Reynolds number, the heat transfer area is reduced, further limiting the efficiency of heat transfer. The ice particles with smaller Reynolds number melt slowly in the early stage, and the temperature of the front end of the ice particles is higher, so that the surface area of the ice particles increases after melting, and the relatively simple wake structure is more conducive to the continuous transfer of heat, so that the volume of the ice particles decreases faster than the ice particles with larger Reynolds number.

[0153] For Reynolds numbers of more than one hundred, the volume fraction of the ice particles decreases more quickly, and decreases to about 96% at t*=26. In the same time scale, the melting amount under high Reynolds number conditions is larger than that under low Reynolds number, indicating that the melting rate under high Reynolds number conditions 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.

[0154] 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 condition of large Reynolds number, the volume loss percentage begins 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 study of ice particle abrasive jet, thereby simplifying the calculation model.

[0155] Preferably, the dimensionless processing includes dimensionless processing of velocity, temperature, length and time, specifically:

[0156] 、 、 、 ;

[0157] wherein, 、 、 、 are dimensionless velocity, temperature, length and time, respectively. , , are the actual velocity, temperature and length, respectively; , are the 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 particle.

[0158] The dimensionless is an indispensable key step in the lattice Boltzmann method, which fundamentally eliminates the influence of the artificially set unit system on the numerical calculation results, and improves the efficiency, stability and universality of the calculation.

[0159] Preferably, the specific step of the step S5 of performing the flow state analysis of the solid two-phase flow is:

[0160] The determined variables are the length-diameter ratio of the mixing chamber, the abrasive incidence angle, the abrasive particle size and the abrasive mass flow rate;

[0161] The affected factors are the nozzle flow field and pressure distribution, the abrasive mass concentration distribution, the abrasive spatial position distribution and the abrasive velocity distribution;

[0162] By using the control variable method, the CFD-DEM coupling model is used to compare and analyze the influence of different variables on the affected factors, and the flow state analysis results are obtained.

[0163] 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 intensity 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:

[0164] (1) With the increase of the length-diameter ratio, the following rules are presented: ① Flow field velocity and pressure: the core area of the jet is contracted, and the pressure of 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 Spatial distribution of abrasives: after the length-diameter ratio increases, 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 staying in the nozzle for less than 0.02s is the largest, which is 85.14%.

[0165] (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 is gradually dispersed, and the pressure of the mixing chamber continuously increases. ② Abrasive mass concentration: the high concentration area gradually diffuses and the distribution range expands. ③ Spatial distribution of abrasives: the accumulation of abrasives at the top first increases and then decreases, and the abrasive distribution is more uniform, which is more conducive to the ejection of abrasives. ④ Abrasive velocity distribution: the tangential velocity of the abrasive in the second half of the focusing tube first decreases and then increases; the velocity in region A is constant, and the velocity in regions B and C slightly decreases and the fluctuation decreases. The proportion of short residence time of abrasives decreases with the decrease of the incident angle.

[0166] (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, and except for the condition of particle size 100 μm, the abrasive distribution is concentrated. ④ Abrasive velocity distribution: the velocity of the abrasive in region A decreases, and the fluctuation of the velocity in regions B and C weakens. The proportion of short residence time of abrasives first increases, then decreases, and then increases, and when dp=100 μm, it is the largest, which is 83.28%.

[0167] (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 is contracted, 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: when the mass flow rate is small, the distribution is uniform, and when the mass flow rate is large, the abrasives gather into a group; with the increase of the mass flow rate, the accumulation at the top intensifies, but the focusing effect in the downstream area is better. ④ Abrasive velocity distribution: the tangential velocity of the abrasive in the second half of the focusing tube decreases slightly; the velocity in regions B and C fluctuates first weakens and then enhances. The proportion of short residence time of abrasives first increases and then decreases, and when Qm=0.3 g / s, it is the largest, which is 85.54%.

[0168] Preferably, the specific step of performing the wear analysis of the nozzle in the step S5 is:

[0169] Determine 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;

[0170] Determine the influencing factors as the normal and tangential cumulative energy and the Oka wear distribution;

[0171] Using the control variable method, the CFD-DEM coupling model is used to compare and analyze the influence of different variables on the influencing factors, and the wear analysis results are obtained.

[0172] As the core component of the jet system, the nozzle's 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, leading to a decrease in jet focusing performance and an increase in energy consumption. The normal and tangential cumulative energy received by the nozzle can be used as an important indicator to measure the wear condition of the component. The greater the cumulative energy on the wall surface, the more likely it is to occur wear behavior and more severe wear. By comparing and analyzing the influence of variables such as the length-diameter ratio of the mixing chamber, the abrasive incidence angle, the abrasive particle size and the 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:

[0173] (1) As the length-diameter ratio increases, 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. As the length-diameter ratio increases 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 inlet section, with the minimum cumulative energy at a length-diameter ratio of 2 and the maximum at a length-diameter ratio of 2.4. The Oka wear region in the entire nozzle first decreases and then increases, with the most severe wear at a length-diameter ratio of 2.4, concentrated in the front end of the mixing chamber and the inlet section of the focusing tube.

[0174] (2) As the incidence angle decreases, the distribution range 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 significantly increased. In the focusing tube section, the normal and tangential cumulative energy is concentrated in the inlet section, with the range first increasing and then decreasing, and the cumulative energy being the largest at an incidence angle of 45° and extending downstream. The Oka wear changes little with the incidence angle, with the severe wear region 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 severe, concentrated in the front end of the mixing chamber and the inlet section of the focusing tube.

[0175] (3) With the increase of abrasive particle size, the distribution area and energy intensity of 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 inlet section, and the relative size is relatively small when the particle size is 110 μm. With the increase of particle size, the severe wear area of Oka wear gradually expands in the contraction section, the top of the mixing chamber and the first half of the focusing tube, and the moderate wear area in the chamber gradually contracts upstream and concentrates.

[0176] (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 energy accumulation is significantly higher than the normal accumulation. In the focusing tube section, the normal and tangential cumulative energy is mostly concentrated in the first half, and the energy peak area gradually increases. With the increase of flow rate from 0.2 g / s to 0.35 g / s, the severe wear area of Oka wear gradually expands in the contraction section and the top of the mixing chamber, and the moderate wear area in the chamber gradually extends downstream. From the aspect of wear quantification, the greater the mass flow rate, the more serious the wear.

[0177] 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.

[0178] Finally, based on the flow state analysis results and the wear analysis results, the four variables are adjusted to provide theoretical support for optimizing the jet process and the nozzle design.

[0179] 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 method of optimizing a post-mix ice abrasive jet nozzle, characterized in that, The method comprises the following steps: Step S1, obtaining the basic parameters of a nozzle to be optimized, and constructing a CFD model for a continuous phase; Step S2, establishing an ice particle database, and establishing a DEM model for a 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 by using 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; 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; The specific steps of the step S4 are: A physical model of the post-mixing abrasive jet nozzle is constructed, the physical model of the post-mixing abrasive jet nozzle comprises a high-pressure water pipeline, a mixing chamber, a contraction transition section and a focusing pipe connected in sequence, and a feed pipe is arranged on the mixing chamber; An LBM model is constructed by using the lattice Boltzmann method, the minimum speed of the ice particle at the outlet of the physical model of the post-mixing abrasive jet nozzle and the time-averaged speed at the outlet of the flow field are selected as the boundary conditions of the LBM model, the LBM model is simplified into a uniform heat flow field, and the ice particle is fixed in 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 result.

2. A method of optimizing a post-mix ice abrasive jet nozzle according to claim 1, wherein, The specific steps of the step S1 are: The inlet end parameters, internal channel parameters and outlet end parameters of the nozzle to be optimized are obtained as the basic parameters; A continuity equation is constructed based on the basic parameters: The initial continuity equation is constructed as: wherein , , respectively represent velocity components of the fluid, is the fluid density, is time, , , are three coordinate axes of a spatial rectangular coordinate system; Bringing in Operator: , , , , are unit vectors of the positive direction of the x-axis, y-axis, and z-axis, respectively, is the velocity vector of the fluid, and when calculating incompressible flow, the fluid density is constant, and the initial continuity equation becomes: ; A momentum conservation equation is constructed 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 denotes static pressure, denotes external forces in the direction, denotes 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 the fluid and the part of mechanical energy converted into heat energy, is the divergence operator, is the temperature gradient, is the constant-pressure specific heat capacity of the fluid; Adopting The model constructs a turbulence model based on basic parameters: ； ； where the effective viscosity , represents the molecular viscosity, 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 due to velocity difference and 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 a correction of the dissipation term due to Reynolds stress.

3. A method of optimizing a post-mix ice abrasive jet nozzle according to claim 1, wherein, The specific steps of the step S2 are: An ice particle collision model including ice particle mass, damping coefficient and elastic coefficient is established: wherein , 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 ice particles collide, the normal overlap is given by: 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 grains is , where , Ei, Ejare the elastic modulus of ice grains i, j, respectively, , vi, vjare the Poisson's ratio of ice grains i, j, respectively. The normal damping force is: , wherein , the expression is: are the masses of particles i and j, respectively, is the relative normal velocity of ice particles i, j: , are the velocity vectors of particles 1 and 2, and n is the unit normal vector when ice particles collide: , and are the vector positions of the sphere centers; tangential force between ice particles is: where is the tangential overlap, is the tangential stiffness: where G* is the equivalent shear modulus: wherein , Gjand Gjare the shear moduli of material i and material j, respectively. The tangential damping force of the ice particle after collision is: A motion control equation of the ice particle is established: ， ， ； where R is the resistance experienced by the ice particle ; 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 Reynolds number of the ice particle, is the drag coefficient, and is the gravitational acceleration and other forces experienced by the particle in addition to the drag force, buoyant-weight force, respectively, and for a spherical ice particle, the drag coefficient is calculated by the following equation: An erosion wear model is established by using the Oka model: where , 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 any impact angle; , are the velocity and diameter of a reference ice particle, respectively; g(a) is a function of the impact angle a; is the mass flow rate; K, a, b, k1, k2, k3, n1, n2 are constants.

4. A method of optimizing a post-mix ice abrasive jet nozzle according to claim 1, wherein, The specific steps of the step S3 are: Step S31, the flow field of one time step is calculated and iterated to convergence by using the CFD model; Step S32, the DEM model starts the calculation of the ice particle phase, and the force and motion 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 steps S31-S33 are cycled to obtain the CFD-DEM coupling model; Step S34, the flow characteristics verification and wear verification of the CFD-DEM coupling model are performed by using a conical nozzle model and a 90° elbow model respectively.

5. A method of optimizing a post-mix ice abrasive jet nozzle according to claim 1, wherein, The dimensionless processing includes dimensionless processing of velocity, temperature, length and time, and specifically: 、 、 、 ； where, , , , are the dimensionless velocity, temperature, length and time, respectively; , , are the actual velocity, temperature and length, respectively; , are the 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 particle.

6. A method of optimizing a post-mix ice abrasive jet nozzle according to claim 1, wherein, The specific steps of the step S5 for performing flow state analysis of solid two-phase flow are: Determine 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; Determine the influencing factors as the nozzle flow field and pressure distribution, the abrasive mass concentration distribution, the abrasive spatial position distribution and the abrasive velocity distribution; The CFD-DEM coupling model is used to analyze the influence of different variables on the affected factors by the control variable method, and the flow state analysis result is obtained.

7. A method of optimizing a post-mix ice abrasive jet nozzle according to claim 6, characterized in that, The specific steps of the step S5 of performing the wear analysis of the nozzle are as follows: The determined variables are the length-diameter ratio of the mixing chamber, the abrasive incidence angle, the abrasive particle size and the abrasive mass flow rate; The determined affected factors are the normal and tangential cumulative energies and the Oka wear distribution; The CFD-DEM coupling model is used to analyze the influence of different variables on the affected factors by the control variable method, and the wear analysis result is obtained.

8. A method of optimizing a post-mix ice abrasive jet nozzle according to claim 7, characterized in that, According to the flow state analysis result and the wear analysis result, the length-diameter ratio of the mixing chamber, the abrasive incidence angle, the abrasive particle size and the abrasive mass flow rate of the nozzle are optimized.

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