CN108804803B - Numerical simulation method for machining variable-diameter pipe by discrete element solid-liquid two-phase abrasive flow based on multiple physical coupling fields - Google Patents
Numerical simulation method for machining variable-diameter pipe by discrete element solid-liquid two-phase abrasive flow based on multiple physical coupling fields Download PDFInfo
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Abstract
The invention relates to a numerical simulation method for discrete element abrasive flow machining based on multiple physical coupling fields, which comprises the following specific steps of: (1) establishing a geometric model of the variable-diameter pipe (the research object of the invention is a fourth-order variable-diameter pipe and a fifth-order variable-diameter pipe); (2) dividing meshes of the variable-caliber pipe flow passage model; (3) setting a CFD-DEM coupling physical parameter; (4) setting boundary conditions in CFD software and DEM software; (5) selecting processing technological parameters; (6) post-processing the CFD-DEM coupling result; the method carries out numerical simulation analysis on the discrete element method of the variable-caliber pipe abrasive flow processing in a plurality of physical coupling fields, the continuous phase and the discrete phase are calculated through CFD-DEM coupling, and the influence of the variable-caliber pipe abrasive flow material removal mechanism and the processing parameters on the variable-caliber pipe abrasive flow processing technology is explored.
Description
Technical Field
The invention relates to a numerical simulation method for discrete element solid-liquid two-phase abrasive flow machining based on multiple physical coupling fields, and belongs to the technical field of solid-liquid two-phase abrasive flow precision machining.
Background
For the solid-liquid two-phase abrasive flow processing technology, the current research work of domestic scholars mainly aims at theoretical research under certain specific conditions, less important parameters are researched in the discrete element solid-liquid two-phase abrasive flow processing process of multiple physical coupling fields, the general guiding significance of the achievements on abrasive flow processing is limited, and for researching the variable-caliber pipe abrasive flow processing technology, the four-order variable-caliber pipe and the five-order variable-caliber pipe work piece are taken as objects, numerical simulation analysis is carried out on solid-liquid two-phase abrasive flow processing under the CFD-DEM coupling condition, and important technical guidance can be provided for actual production.
Disclosure of Invention
The invention aims to provide a numerical simulation method for discrete element solid-liquid two-phase abrasive flow machining based on multiple physical coupling fields, so as to provide important technical guidance for actual production.
In order to achieve the purpose, the technical scheme of the invention is as follows:
a numerical simulation method for discrete element abrasive flow machining based on multiple physical coupling fields comprises the following specific steps:
(1) establishing a physical model of the variable-caliber pipe: selecting a four-order variable-diameter pipe and a five-order variable-diameter pipe by taking the variable-diameter pipe as a research object, wherein the four-order variable-diameter pipe is in a step shape, the inner diameter of each step of the four-order variable-diameter pipe is phi 1.2mm, phi 1.0mm, phi 0.8mm and phi 0.6mm in sequence, the five-order variable-diameter pipe is in a symmetrical shape, the inner diameter of each step of the five-order variable-diameter pipe is phi 1.0mm, phi 0.8mm, phi 0.6mm, phi 0.8mm and phi 1.0mm in sequence, carrying out geometric model establishment on the four-order variable-diameter pipe and the five-order variable-diameter pipe by utilizing SolidWorks software, and carrying out discrete element calculation on the flow characteristic of the two-phase flow in the variable-diameter pipe passage by adopting different models;
(2) Gridding of the physical model: respectively carrying out grid division on a four-order variable-diameter pipe and a five-order variable-diameter pipe flow channel model by using ICEM software, selecting hexahedral grids to respectively carry out grid division on the four-order variable-diameter pipe and the five-order variable-diameter pipe, carrying out block processing on the flow channel model according to the geometric shape of the model, forming 441106 nodes by using the four-order variable-diameter pipe after grid division, forming 490113 nodes by using the five-order variable-diameter pipe, detecting the quality of a non-structural grid after grid division is finished, wherein the negative volume cannot exist, and the grid quality is more than 0.3;
(3) setting physical model parameters: when multi-physical coupling field CFD-DEM coupling numerical analysis is carried out, parameters are required to be set in CFD software and DEM software respectively, so that a continuous phase is set in the CFD software, a discrete phase is set in the DEM software, an adopted grinding medium is configured by aviation kerosene, an active agent and boron carbide abrasive particles, the aviation kerosene and the active agent are adopted in the continuous phase, and the boron carbide abrasive particles are adopted in the discrete phase;
(4) setting of boundary conditions: in the CFD software, the inlet and outlet conditions, the adopted model, the calculation method, the physical parameters and the wall surface conditions need to be set for numerical simulation calculation, in the DEM software, the discrete phase abrasive particle parameters, the abrasive particle shape, the abrasive particle size and the workpiece material need to be set, and the four-step variable-diameter pipe and the five-step variable-diameter pipe are set as follows:
(a) The model is adopted: according to Reynolds number equation
Calculating rho-fluid density mill, v-fluid velocity, D-workpiece inlet aperture and eta-viscosity coefficient; the flow of the grinding material can form a turbulent flow state, and a k-epsilon turbulent flow model is adopted; in CFD software, an RNG Model (RNG k-epsilon two-equation Model, and an RNG (Re-normalization group) is a turbulence Model in fluid mechanics) is selected from a k-epsilon Model, Standard Wall Functions are selected from a Near-Wall Treatment, and Transient (Transient calculation) is selected from Time;
(b) entrance boundary setting:
continuous phases are set in the CFD software: the continuous phase is selected from aviation kerosene and an oiliness agent, the inlet condition adopts a speed inlet condition, the hydraulic radius is actually set to be 3mm, the inlet speed is vertical to an inlet boundary surface, different speeds are selected through simulation calculation, and the gravity direction is the same as the inlet speed;
setting discrete phases in DEM software: the discrete phase is boron carbide abrasive particles, the inlet condition also adopts a speed inlet condition, the initial speed which is the same as that of the continuous phase is set, in order to simplify an abrasive particle model, the abrasive particles are simplified into a spherical shape, different abrasive particle diameters are selected through simulation calculation, and the gravity direction of the abrasive particles is consistent with the speed direction of the abrasive particles;
(c) Setting an outlet boundary: the Outlet boundary conditions in the solid-liquid two-phase mainly comprise a Pressure Outlet (Pressure Outlet) and a mass Outlet (Outlet), the liquid phase is an incompressible fluid, the actual conditions of polishing the four-step variable-diameter pipe and the five-step variable-diameter pipe by abrasive flow can be known, the speed and the Pressure of abrasive particles flowing out of a workpiece are difficult to measure, the Outlet end is communicated with the outside, and therefore the continuous phase Outlet boundary condition is set as a free Outlet;
(d) setting wall surface boundaries: the wall surface condition adopts an enhanced wall surface function method and a non-slip wall surface condition;
(e) DEM software workpiece material setting: according to the actual abrasive flow machining, a fourth-order variable-diameter pipe and a fifth-order variable-diameter pipe are made of 304 stainless steel materials;
(f) DEM software abrasive grain factory settings: according to a Lagrange method, the concentration of discrete phase abrasive is not more than 10%, Dynamic model is selected in Fartory Type, Linear speed is selected in Velocity, the direction of abrasive particle speed is the same as that of continuous phase aviation kerosene and active agent, according to the structural characteristics of a four-step variable-diameter pipe and a five-step variable-diameter pipe and the size of abrasive particles, the time step length is set to be 2e-7s in DEM software, the Track colloids (abrasive particle tracking collision) is started, and the total numerical simulation time is 1 s;
(g) CFD-DEM coupling setup: in the CFD-DEM coupling process, the ratio of the time step in DEM software to the time step in CFD software is 1:1 to 100:1, and the time step in DEM software cannot be larger than that in CFD software; an Euler-Lagrange method is selected for coupling, Sample Points are set to be 10, one abrasive particle can move in 10 grids, the size of the Sample Points is increased, and the stability of simulation can be increased; setting the moment Under-relaxation to 0.7, reducing the relaxation factor and being easier to converge, and increasing the stability of the simulation, but the calculation speed becomes slow, so that Under the condition of simulating the stability, selecting a proper relaxation factor;
(5) selecting abrasive flow processing parameters: when the four-order variable-caliber pipe, the five-order variable-caliber pipe and numerical simulation are carried out, the selected abrasive flow processing factors comprise: inlet velocity, abrasive concentration, abrasive particle size; the four selected parameter data are that the inlet speed is 30m/s, 35m/s, 40m/s and 45m/s, the abrasive concentration is 4%, 6%, 8% and 10%, and the grain size is 300 meshes, 400 meshes, 500 meshes and 800 meshes.
(6) Numerical simulation results and analysis: numerical simulation is carried out on the variable-caliber pipe abrasive flow processing technology by adopting a discrete element method, and the influence of the variable-caliber pipe abrasive flow material removal mechanism and the processing parameters on the variable-caliber pipe abrasive flow processing technology is explored;
(7) Post-processing the CFD-DEM coupling result; (a) displaying the continuous phase and the discrete phase by applying Ensight software; (b) the discrete phase abrasive particles are distributed and displayed at different time; (c) displaying continuous phase dynamic pressure and turbulent flow kinetic energy and discrete phase abrasive particle total energy and kinetic energy under the condition of different inlet speeds when the four-order variable-diameter pipe and the five-order variable-diameter pipe are subjected to numerical simulation analysis; displaying the continuous phase speed and turbulence intensity, and the discrete phase abrasive particle speed and kinetic energy under the conditions of different abrasive concentrations; the continuous phase turbulent dissipation rate and turbulent viscosity and the discrete phase abrasive kinetic energy and speed are displayed under the condition of different abrasive particle diameters, and the continuous phase speed and dynamic pressure, the abrasive particle speed and total energy are displayed under the condition of different incident angles.
In the CFD-DEM coupling method in the calculation and solution process, the numerical simulation setting is carried out according to the physical model size parameter of the variable-diameter pipe and the abrasive flow processing condition, and the convergence residual curve of the CFD-DEM coupling of the variable-diameter pipe is obtained through solution and calculation; with the increase of the iteration times, the residual error curve of each parameter iteration 1500 times of the model calculation solution is stable, which indicates that the solid-liquid two-phase abrasive flow processing reaches a stable turbulent state after a period of time under the CFD-DEM coupling condition, and the setting of the coupling solution parameters and the model design of the variable-caliber pipe solid-liquid two-phase abrasive flow processing CFD-DEM is reasonable; in order to obtain the motion characteristics of solid-liquid two-phase abrasive particle flow processing of the variable-diameter pipe in a CFD-DEM coupling downstream field, when numerical simulation is carried out on a fourth-order variable-diameter pipe and a fifth-order variable-diameter pipe, the dynamic pressure and turbulence kinetic energy of fluid with different inlet speeds in the CFD-DEM coupling field, the total energy and kinetic energy of abrasive particles, the fluid speed and turbulence intensity of fluid with different abrasive concentrations in the CFD-DEM coupling field, the abrasive particle speed and kinetic energy, the fluid turbulence dissipation rate and turbulence viscosity of different abrasive particle sizes in the CFD-DEM coupling field, the kinetic energy and speed of abrasive particles, the fluid speed and dynamic pressure, abrasive particle speed and total energy of different incident angles in the CFD-DEM coupling field are analyzed, and the influence of each parameter factor on the grinding effect is researched and analyzed;
(1) Influence of inlet speed on material removal of the four-step variable-diameter pipe and the five-step variable-diameter pipe: by analyzing the distribution characteristics of fluid dynamic pressure, turbulent flow kinetic energy, abrasive particle total energy and kinetic energy of the four-order variable-caliber pipe and the five-order variable-caliber pipe workpieces under different inlet speeds, the inlet speed of the abrasive particle flow polishing workpiece is increased, the dynamic pressure and the turbulent flow kinetic energy are increased, and therefore the polishing quality of the inner surface of the four-order variable-caliber pipe can be effectively improved. Meanwhile, the total energy and the kinetic energy of the abrasive particles are increased, the larger the total energy and the kinetic energy are, the more violent the collision is on the wall surface of the workpiece, the larger the removal amount of the surface material of the workpiece is, and the polishing processing of the wall surface by abrasive particle flow is facilitated;
(2) the influence of the abrasive concentration on the removal of the workpiece materials of the four-order variable-diameter pipe and the five-order variable-diameter pipe is as follows: by analyzing the distribution characteristics of fluid speed, turbulence intensity, abrasive particle speed and kinetic energy of the four-order variable-diameter pipe and the five-order variable-diameter pipe under different abrasive concentration conditions, the abrasive concentration is increased, the number of times of collision of abrasive particles on the wall surface is increased, and therefore the polishing processing effect on the wall surface is facilitated. According to the Lagrange calculation method, the abrasive concentration is less than 10%, and in the range, the higher the abrasive concentration is, the larger the abrasive quantity close to the wall surface is, the material removal amount is improved, and the precise processing effect of abrasive flow on the wall surface is facilitated;
(3) Influence of abrasive particle size on removal of workpiece materials of the fourth-order variable-diameter pipe and the fifth-order variable-diameter pipe: by analyzing the distribution characteristics of fluid turbulence dissipation rate, turbulence viscosity, abrasive particle kinetic energy and speed of the four-order variable-diameter pipe and the five-order variable-diameter pipe under the conditions of different abrasive particle sizes, the removal rate and the surface quality of the surface material of the workpiece are improved by means of abrasive particles with different particle sizes; the smaller the grain diameter of the abrasive particles is, the better the liquid flow following performance is, the randomness of the liquid turbulent motion is utilized to randomly cut the workpiece, and the polishing randomness is beneficial to the uniformity of the precision processing of the abrasive particle flow; the larger the grain diameter of the abrasive grains is, the more the abrasive grains can scrape the wall surface for a long time, the more the number of times of collision is than that of the abrasive grains with small grain diameter, and the removal rate of the material can be improved;
(4) influence of incident angle on material removal of the fourth-order variable-diameter pipe and the fifth-order variable-diameter pipe: by analyzing the distribution characteristics of fluid velocity, dynamic pressure, abrasive particle velocity and total energy of the four-order variable-diameter pipe and the five-order variable-diameter pipe under different incident angles, the incident angle is changed to change the flow field distribution in the four-order variable-diameter pipe and the five-order variable-diameter pipe.
Drawings
FIG. 1 is a two-dimensional model of a four-step variable-caliber pipe;
FIG. 2 is a two-dimensional model diagram of a five-step variable-caliber pipe;
FIG. 3 is a schematic diagram of a flow channel part of a four-step variable-caliber pipe two-dimensional model divided into regions;
FIG. 4 is a schematic diagram of a flow channel part dividing region of a five-step variable-caliber pipe two-dimensional model.
Detailed Description
(1) Establishing a physical model of the variable-caliber pipe: selecting a four-order variable-diameter pipe and a five-order variable-diameter pipe by taking the variable-diameter pipe as a research object, wherein the four-order variable-diameter pipe is in a step shape, the inner diameter of each step of the four-order variable-diameter pipe is phi 1.2mm, phi 1.0mm, phi 0.8mm and phi 0.6mm in sequence, the five-order variable-diameter pipe is in a symmetrical shape, the inner diameter of each step of the five-order variable-diameter pipe is phi 1.0mm, phi 0.8mm, phi 0.6mm, phi 0.8mm and phi 1.0mm in sequence, carrying out geometric model establishment on the four-order variable-diameter pipe and the five-order variable-diameter pipe by utilizing SolidWorks software, and carrying out discrete element calculation on the flow characteristic of the two-phase flow in the variable-diameter pipe passage by adopting different models;
(2) gridding of the physical model: respectively carrying out grid division on a four-order variable-diameter pipe and a five-order variable-diameter pipe flow channel model by using ICEM software, selecting hexahedral grids to respectively carry out grid division on the four-order variable-diameter pipe and the five-order variable-diameter pipe, carrying out block processing on the flow channel model according to the geometric shape of the model, forming 441106 nodes by using the four-order variable-diameter pipe after grid division, forming 490113 nodes by using the five-order variable-diameter pipe, detecting the quality of a non-structural grid after grid division is finished, wherein the negative volume cannot exist, and the grid quality is more than 0.3;
(3) Setting physical model parameters: when multi-physical coupling field CFD-DEM coupling numerical analysis is carried out, parameters are required to be set in CFD software and DEM software respectively, so that a continuous phase is set in the CFD software, a discrete phase is set in the DEM software, an adopted grinding medium is configured by aviation kerosene, an active agent and boron carbide abrasive particles, the aviation kerosene and the active agent are adopted in the continuous phase, and the boron carbide abrasive particles are adopted in the discrete phase;
(4) setting of boundary conditions: in the CFD software, the inlet and outlet conditions, the adopted model, the calculation method, the physical parameters and the wall surface conditions need to be set for numerical simulation calculation, in the DEM software, the discrete phase abrasive particle parameters, the abrasive particle shape, the abrasive particle size and the workpiece material need to be set, and the four-step variable-diameter pipe and the five-step variable-diameter pipe are set as follows:
(a) the model is adopted: according to Reynolds number equation
Calculating rho-fluid density mill, v-fluid velocity, D-workpiece inlet aperture and eta-viscosity coefficient; the abrasive flow can form a turbulent flow state, and a k-epsilon turbulent flow model is adopted; in CFD software, an RNG Model (RNG k-epsilon two-equation Model, and an RNG (Re-normalization group) is a turbulence Model in fluid mechanics) is selected from a k-epsilon Model, Standard Wall Functions are selected from a Near-Wall Treatment, and Transient (Transient calculation) is selected from Time;
(b) Entrance boundary setting: setting continuous phases in CFD software: selecting aviation kerosene and an oiliness agent as continuous phases, adopting a speed inlet condition as an inlet condition, setting the hydraulic radius to be 3mm according to the actual condition, setting the inlet speed to be vertical to an inlet boundary surface, selecting different speeds through simulation calculation, and enabling the gravity direction to be the same as the inlet speed;
setting discrete phases in DEM software: the discrete phase is boron carbide abrasive particles, the inlet condition also adopts a speed inlet condition, the initial speed which is the same as that of the continuous phase is set, in order to simplify an abrasive particle model, the abrasive particles are simplified into a spherical shape, different abrasive particle diameters are selected through simulation calculation, and the gravity direction of the abrasive particles is consistent with the speed direction of the abrasive particles;
(c) outlet boundary setting: the Outlet boundary conditions in the solid-liquid two-phase mainly comprise a Pressure Outlet (Pressure Outlet) and a mass Outlet (Outlet), the liquid phase is an incompressible fluid, the actual conditions of polishing the four-step variable-diameter pipe and the five-step variable-diameter pipe by abrasive flow can be known, the speed and the Pressure of abrasive particles flowing out of a workpiece are difficult to measure, the Outlet end is communicated with the outside, and therefore the continuous phase Outlet boundary condition is set as a free Outlet;
(d) setting wall surface boundaries: the wall surface condition adopts an enhanced wall surface function method and a non-slip wall surface condition;
(e) DEM software workpiece material setting: according to the actual abrasive flow processing, a fourth-order variable-diameter pipe and a fifth-order variable-diameter pipe are made of 304 stainless steel materials;
(f) DEM software abrasive grain factory settings: according to a Lagrange method, the concentration of discrete phase abrasives is not more than 10%, a Dynamic model is selected in a Fartory Type, a Linear Velocity is selected in a Velocity, the direction of the abrasive particle Velocity is the same as the direction of continuous phase aviation kerosene and an active agent, according to the structural characteristics of a four-step variable-diameter pipe and a five-step variable-diameter pipe and the size of the abrasive particles, the time step length is set to be 2e-7s in DEM software, the Track colloids (abrasive particle tracking collision) is started, and the total numerical simulation time is 1 s;
(g) CFD-DEM coupling setup: in the CFD-DEM coupling process, the ratio of the time step in DEM software to the time step in CFD software is 1:1 to 100:1, and the time step in DEM software cannot be larger than that in CFD software; an Euler-Lagrange method is selected for coupling, Sample Points are set to be 10, one abrasive particle can move in 10 grids, the size of the Sample Points is increased, and the stability of simulation can be increased; setting the moment Under-relaxation to 0.7, reducing the relaxation factor and being easier to converge, and increasing the stability of the simulation, but the calculation speed becomes slow, so that Under the condition of simulating the stability, selecting a proper relaxation factor;
(5) Selecting abrasive flow processing parameters: when the four-order variable-caliber pipe, the five-order variable-caliber pipe and numerical simulation are carried out, the selected abrasive flow processing factors comprise: inlet velocity, abrasive concentration, abrasive particle size; the four selected groups of parameter data are that the inlet speeds are 30m/s, 35m/s, 40m/s and 45m/s, the abrasive concentration is 4%, 6%, 8% and 10%, and the grain diameters of the abrasive grains are 300 meshes, 400 meshes, 500 meshes and 800 meshes;
(6) post-processing the CFD-DEM coupling result; (a) displaying the continuous phase and the discrete phase by applying Ensight software; (b) the discrete phase abrasive particles are distributed and displayed at different time; (c) displaying continuous phase dynamic pressure and turbulent flow kinetic energy and discrete phase abrasive particle total energy and kinetic energy under the condition of different inlet speeds when the four-order variable-diameter pipe and the five-order variable-diameter pipe are subjected to numerical simulation analysis; displaying the continuous phase speed and turbulence intensity, and the discrete phase abrasive particle speed and kinetic energy under the conditions of different abrasive concentrations; the continuous phase turbulent dissipation rate and turbulent viscosity and the discrete phase abrasive kinetic energy and speed are displayed under the condition of different abrasive particle diameters, and the continuous phase speed and dynamic pressure, the abrasive particle speed and total energy are displayed under the condition of different incident angles.
In the computational solution process, the CFD-DEM coupling method is characterized in that numerical simulation setting is carried out according to the physical model size parameters of the variable-diameter pipe and the abrasive flow machining working condition, and a convergence residual error curve of the variable-diameter pipe CFD-DEM coupling is obtained through solution computation; with the increase of the iteration times, the residual error curve of each parameter iteration 1500 times of the model calculation solution is stable, which indicates that the solid-liquid two-phase abrasive flow processing reaches a stable turbulent state after a period of time under the CFD-DEM coupling condition, and the setting of the coupling solution parameters and the model design of the variable-caliber pipe solid-liquid two-phase abrasive flow processing CFD-DEM is reasonable; in order to obtain the motion characteristics of solid-liquid two-phase abrasive particle flow processing of the variable-diameter pipe in a CFD-DEM coupling downstream field, when numerical simulation is carried out on a fourth-order variable-diameter pipe and a fifth-order variable-diameter pipe, the dynamic pressure and turbulence kinetic energy of fluid with different inlet speeds in the CFD-DEM coupling field, the total energy and kinetic energy of abrasive particles, the fluid speed and turbulence intensity of fluid with different abrasive concentrations in the CFD-DEM coupling field, the abrasive particle speed and kinetic energy, the fluid turbulence dissipation rate and turbulence viscosity of different abrasive particle sizes in the CFD-DEM coupling field, the kinetic energy and speed of abrasive particles, the fluid speed and dynamic pressure, abrasive particle speed and total energy of different incident angles in the CFD-DEM coupling field are analyzed, and the influence of each parameter factor on the grinding effect is researched and analyzed;
(1) Influence of inlet speed on material removal of the four-step variable-diameter pipe and the five-step variable-diameter pipe: by analyzing the distribution characteristics of fluid dynamic pressure, turbulent flow kinetic energy, abrasive particle total energy and kinetic energy of the four-order variable-caliber pipe and the five-order variable-caliber pipe workpieces under different inlet speeds, the inlet speed of the abrasive particle flow polishing workpiece is increased, the dynamic pressure and the turbulent flow kinetic energy are increased, and therefore the polishing quality of the inner surface of the four-order variable-caliber pipe can be effectively improved. Meanwhile, the total energy and the kinetic energy of the abrasive particles are increased, the larger the total energy and the kinetic energy are, the more violent the collision is on the wall surface of the workpiece, the larger the removal amount of the surface material of the workpiece is, and the polishing processing of the wall surface by abrasive particle flow is facilitated;
(2) influence of abrasive concentration on material removal of a four-step variable-diameter pipe and a five-step variable-diameter pipe workpiece: by analyzing the distribution characteristics of fluid speed, turbulence intensity, abrasive particle speed and kinetic energy of the four-order variable-diameter pipe and the five-order variable-diameter pipe under different abrasive concentration conditions, the abrasive concentration is increased, the number of times of collision of abrasive particles on the wall surface is increased, and therefore the polishing processing effect on the wall surface is facilitated. According to the Lagrange calculation method, the abrasive concentration is less than 10%, and in the range, the higher the abrasive concentration is, the larger the abrasive quantity close to the wall surface is, the material removal amount is improved, and the precise processing effect of abrasive flow on the wall surface is facilitated;
(2) Effect of abrasive concentration on four-step caliber-variable pipe material removal: through analyzing the distribution characteristics of fluid velocity, turbulence intensity, abrasive particle velocity and kinetic energy of the four-step variable-diameter pipe under different abrasive concentration conditions, the abrasive concentration is increased, the number of times of collision of abrasive particles on the wall surface is increased, and therefore the polishing processing effect on the wall surface is facilitated. According to the Lagrange calculation method, the abrasive concentration should be less than 10%, and in the range, the larger the concentration is, the larger the number of the abrasive particles close to the wall surface is favorably increased, the material removal amount is increased, and the polishing effect on the wall surface is favorably realized.
(3) The influence of the grain size of the abrasive particles on the removal of the workpiece materials of the four-order variable-diameter pipe and the five-order variable-diameter pipe is as follows: by analyzing the distribution characteristics of fluid turbulence dissipation rate, turbulence viscosity, abrasive particle kinetic energy and speed of the four-order variable-diameter pipe and the five-order variable-diameter pipe under the conditions of different abrasive particle sizes, the removal rate and the surface quality of the surface material of the workpiece are improved by means of abrasive particles with different particle sizes; the smaller the grain diameter of the abrasive particles is, the better the liquid flow following performance is, the randomness of the liquid turbulent motion is utilized to randomly cut the workpiece, and the polishing randomness is beneficial to the uniformity of the precision processing of the abrasive particle flow; the larger the grain size of the abrasive grains is, the longer the abrasive grains can scrape the wall surface, the more the number of times of collision is greater than that of the abrasive grains with small grain size, and the material removal rate can be improved;
(4) Influence of incident angle on material removal of the fourth-order variable-diameter pipe and the fifth-order variable-diameter pipe: by analyzing the distribution characteristics of fluid velocity, dynamic pressure, abrasive particle velocity and total energy of the four-order variable-diameter pipe and the five-order variable-diameter pipe under different incident angles, the incident angle is changed to change the flow field distribution in the four-order variable-diameter pipe and the five-order variable-diameter pipe.
Claims (2)
1. A numerical simulation method for discrete element abrasive flow machining based on multiple physical coupling fields is characterized in that: the method comprises the following specific steps:
(1) establishing a physical model of the variable-caliber pipe: selecting a four-order variable-diameter pipe and a five-order variable-diameter pipe by taking the variable-diameter pipe as a research object, wherein the four-order variable-diameter pipe is in a step shape, the inner diameter of each step of the four-order variable-diameter pipe is phi 1.2mm, phi 1.0mm, phi 0.8mm and phi 0.6mm in sequence, the five-order variable-diameter pipe is in a symmetrical shape, the inner diameter of each step of the five-order variable-diameter pipe is phi 1.0mm, phi 0.8mm, phi 0.6mm, phi 0.8mm and phi 1.0mm in sequence, carrying out geometric model establishment on the four-order variable-diameter pipe and the five-order variable-diameter pipe by utilizing SolidWorks software, and carrying out discrete element calculation on the flow characteristic of the two-phase flow in the variable-diameter pipe passage by adopting different models;
(2) Grid division of the variable-caliber pipe flow channel physical model: respectively carrying out grid division on a four-order variable-diameter pipe and a five-order variable-diameter pipe flow channel model by using ICEM software, selecting hexahedral grids to respectively carry out grid division on the four-order variable-diameter pipe and the five-order variable-diameter pipe, carrying out block processing on the flow channel model according to the geometric shape of the model, forming 441106 nodes by using the four-order variable-diameter pipe after grid division, forming 490113 nodes by using the five-order variable-diameter pipe, detecting the quality of a non-structural grid after grid division is finished, wherein the negative volume cannot exist, and the grid quality is more than 0.3;
(3) and (3) setting parameters of the CFD-DEM coupling physical model: when multi-physical coupling field CFD-DEM coupling numerical analysis is carried out, parameters are required to be set in CFD software and DEM software respectively, so that a continuous phase is set in the CFD software, a discrete phase is set in the DEM software, an adopted grinding medium is configured by aviation kerosene, an active agent and boron carbide abrasive particles, the aviation kerosene and the active agent are adopted in the continuous phase, and the boron carbide abrasive particles are adopted in the discrete phase;
(4) setting boundary conditions in CFD software and DEM software: in the CFD software, the inlet and outlet conditions, the adopted model, the calculation method, the physical parameters and the wall surface conditions need to be set for numerical simulation calculation, in the DEM software, the discrete phase abrasive particle parameters, the abrasive particle shape, the abrasive particle size and the workpiece material need to be set, and the four-step variable-diameter pipe and the five-step variable-diameter pipe are set as follows:
(a) The model is adopted:
according to Reynolds number equation
Calculating, rho-fluid density, v-fluid velocity, D-workpiece entryPore size, η -viscosity coefficient; the abrasive flow can form a turbulent flow state, and a k-epsilon turbulent flow model is adopted; in CFD software, selecting an RNG Model from a k-epsilon Model, selecting Standard Wall Functions from Near-Wall strategies, and selecting a transition from Time;
(b) entrance boundary setting:
continuous phases are set in the CFD software: selecting aviation kerosene and an oiliness agent as continuous phases, adopting a speed inlet condition as an inlet condition, setting the hydraulic radius to be 3mm according to the actual condition, setting the inlet speed to be vertical to an inlet boundary surface, selecting different speeds through simulation calculation, and enabling the gravity direction to be the same as the inlet speed;
setting discrete phases in DEM software: the discrete phase is boron carbide abrasive particles, the inlet condition also adopts a speed inlet condition, the initial speed which is the same as that of the continuous phase is set, in order to simplify an abrasive particle model, the abrasive particles are simplified into a spherical shape, different abrasive particle diameters are selected through simulation calculation, and the gravity direction of the abrasive particles is consistent with the speed direction of the abrasive particles;
(c) outlet boundary setting:
the outlet boundary conditions in the solid-liquid two phases mainly comprise a pressure outlet and a mass outlet, the liquid phase is incompressible fluid, the actual conditions of polishing the four-step variable-diameter pipe and the five-step variable-diameter pipe by abrasive flow can be known, the speed and the pressure of abrasive particles flowing out of a workpiece are difficult to measure, the outlet end is communicated with the outside, and therefore the boundary conditions of the continuous phase outlet are set as a free outlet;
(d) Setting wall surface boundaries:
the wall surface condition adopts an enhanced wall surface function method and a non-slip wall surface condition;
(e) DEM software workpiece material setting:
according to the actual abrasive flow processing, a fourth-order variable-diameter pipe and a fifth-order variable-diameter pipe are made of 304 stainless steel materials;
(f) DEM software abrasive grain factory settings:
according to a Lagrange method, the concentration of discrete phase abrasives is not more than 10%, Dynamic is selected in a Fartory Type, Linear is selected in Velocity, the direction of abrasive particle speed is the same as the direction of continuous phase aviation kerosene and an active agent, according to the structural characteristics of a four-order variable-diameter pipe and a five-order variable-diameter pipe and the size of abrasive particles, the time step length is set to be 2e-7s in DEM software, the Track colloids is started, and the total numerical simulation time is 1 s;
(g) CFD-DEM coupling setup:
in the CFD-DEM coupling process, the ratio of the time step in DEM software to the time step in CFD software is 1:1 to 100:1, and the time step in DEM software cannot be larger than that in CFD software; an Euler-Lagrange method is selected for coupling, Sample Points are set to be 10, one abrasive particle can move in 10 grids, the size of the Sample Points is increased, and the stability of simulation can be increased; setting the moment Under-relaxation to 0.7, reducing the relaxation factor and being easier to converge, and increasing the stability of the simulation, but the calculation speed becomes slow, so that the relaxation factor is selected Under the condition of simulating the stability;
(5) Selecting abrasive flow processing technological parameters: when the numerical simulation of the four-order variable-diameter pipe and the five-order variable-diameter pipe is carried out, the selected abrasive flow processing factors comprise: inlet velocity, abrasive concentration, abrasive particle size; the four selected groups of parameter data are that the inlet speeds are 30m/s, 35m/s, 40m/s and 45m/s, the abrasive concentration is 4%, 6%, 8% and 10%, and the grain diameters of the abrasive grains are 300 meshes, 400 meshes, 500 meshes and 800 meshes;
(6) post-processing the CFD-DEM coupling result;
(a) displaying the continuous phase and the discrete phase by applying Ensight software;
(b) the discrete phase abrasive particles are distributed and displayed at different time;
(c) displaying continuous phase dynamic pressure and turbulent flow kinetic energy and discrete phase abrasive particle total energy and kinetic energy under the condition of different inlet speeds when the four-order variable-diameter pipe and the five-order variable-diameter pipe are subjected to numerical simulation analysis; displaying the continuous phase speed and turbulence intensity, and the discrete phase abrasive particle speed and kinetic energy under the conditions of different abrasive concentrations; the continuous phase turbulent dissipation rate and turbulent viscosity and the discrete phase abrasive kinetic energy and speed are displayed under the condition of different abrasive particle diameters, and the continuous phase speed and dynamic pressure, the abrasive particle speed and total energy are displayed under the condition of different incident angles.
2. The method of claim 1, wherein the method comprises the steps of: in the CFD-DEM coupling method in the calculation and solution process, the numerical simulation setting is carried out according to the physical model size parameter of the variable-diameter pipe and the abrasive flow processing condition, and the convergence residual curve of the CFD-DEM coupling of the variable-diameter pipe is obtained through solution and calculation; with the increase of the iteration times, the residual error curve of each parameter iteration 1500 times of the model calculation solution is stable, which indicates that the solid-liquid two-phase abrasive flow processing reaches a stable turbulent state after a period of time under the CFD-DEM coupling condition, and the setting of the coupling solution parameters and the model design of the variable-caliber pipe solid-liquid two-phase abrasive flow processing CFD-DEM is reasonable; in order to obtain the motion characteristics of solid-liquid two-phase abrasive particle flow processing of the variable-diameter pipe in a CFD-DEM coupling downstream field, when numerical simulation is carried out on a fourth-order variable-diameter pipe and a fifth-order variable-diameter pipe, the dynamic pressure and turbulence kinetic energy of fluid with different inlet speeds in the CFD-DEM coupling field, the total energy and kinetic energy of abrasive particles, the fluid speed and turbulence intensity of fluid with different abrasive concentrations in the CFD-DEM coupling field, the abrasive particle speed and kinetic energy, the fluid turbulence dissipation rate and turbulence viscosity of different abrasive particle sizes in the CFD-DEM coupling field, the kinetic energy and speed of abrasive particles, the fluid speed and dynamic pressure, abrasive particle speed and total energy of different incident angles in the CFD-DEM coupling field are analyzed, and the influence of each parameter factor on the grinding effect is researched and analyzed;
(1) The influence of the inlet speed on the removal of the workpiece materials of the four-order variable-diameter pipe and the five-order variable-diameter pipe is as follows:
by analyzing the distribution characteristics of fluid dynamic pressure, turbulent flow kinetic energy, total energy of abrasive particles and kinetic energy of a workpiece of the fourth-order variable-diameter pipe and the fifth-order variable-diameter pipe under the conditions of different inlet speeds, the inlet speed of the workpiece polished by abrasive particle flow is increased, and the dynamic pressure and the turbulent flow kinetic energy are increased, so that the polishing quality of the inner surface of the fourth-order variable-diameter pipe can be effectively improved, meanwhile, the total energy and the kinetic energy of the abrasive particles are increased, the larger the total energy and the kinetic energy are, the stronger the collision on the wall surface of the workpiece is, the larger the removal amount of the surface material of the workpiece is, and the polishing processing of the wall surface by the abrasive particle flow is facilitated;
(2) influence of abrasive concentration on material removal of a four-step variable-diameter pipe and a five-step variable-diameter pipe workpiece:
by analyzing the distribution characteristics of fluid velocity, turbulence intensity, abrasive particle velocity and kinetic energy of a fourth-order variable-diameter pipe and a fifth-order variable-diameter pipe workpiece under different abrasive material concentration conditions, the abrasive material concentration is increased, the number of times of collision of abrasive particles on the wall surface is increased, so that the polishing processing effect on the wall surface is facilitated, the fourth-order variable-diameter pipe and the fifth-order variable-diameter pipe workpiece are small-aperture pipes, the concentration is too large, the aperture is likely to be blocked, the flowability of the abrasive particles is not facilitated, the abrasive material concentration is less than 10% according to a Lagrange calculation method, the concentration is higher in the range, the number of the abrasive particles close to the wall surface is facilitated to be increased, the material removal amount is improved, and the precise processing effect of abrasive particle flow on the wall surface is facilitated;
(3) Influence of abrasive particle size on removal of workpiece materials of the fourth-order variable-diameter pipe and the fifth-order variable-diameter pipe:
by analyzing the distribution characteristics of fluid turbulence dissipation rate, turbulence viscosity, abrasive particle kinetic energy and speed of the four-order variable-diameter pipe and the five-order variable-diameter pipe under the conditions of different abrasive particle sizes, the removal rate and the surface quality of the surface material of the workpiece are improved by the abrasive particles with different particle sizes; the smaller the grain diameter of the abrasive particles is, the better the liquid flow following performance is, the randomness of the liquid turbulent motion is utilized to randomly cut the workpiece, and the polishing randomness is favorable for the uniformity of the precision processing of the abrasive particle flow; the larger the grain diameter of the abrasive grains is, the more the abrasive grains can scrape the wall surface for a long time, the more the number of times of collision is than that of the abrasive grains with small grain diameter, and the removal rate of the material can be improved;
(4) influence of incident angle on material removal of the fourth-order variable-diameter pipe and the fifth-order variable-diameter pipe:
by analyzing the distribution characteristics of fluid velocity, dynamic pressure, abrasive particle velocity and total energy of the four-order variable-diameter pipe and the five-order variable-diameter pipe under different incident angles, the incident angle is changed to change the distribution of the flow field in the four-order variable-diameter pipe and the five-order variable-diameter pipe.
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