Plasma spraying jet flow numerical simulation method based on equivalent heat source model

Abstract

The invention discloses a plasma spraying jet flow numerical simulation method based on an equivalent heat source model. The method comprises the steps that a jet flow physical model is established, and grids are divided; solving the coupling turbulence model, the component transport model and the equivalent heat source model; selecting different boundary conditions and heat source parameters according to different working conditions; calculating to obtain a convergence result and comparing the convergence result with a test value; the jet flow characteristic calculation process under different spraying modes (non-transferred arc, combined arc and transferred arc) in plasma spraying is unified. The method has the characteristic of reducing the test cost for monitoring the plasma jet.

Description

Technical Field

[0001] The present invention relates to the field of thermal spraying technology, and more particularly to a plasma spraying jet numerical simulation method based on an equivalent heat source model. Background Art

[0002] As the service environment of various mechanical equipment under harsh working conditions such as high temperature, high humidity, and high pressure becomes more complicated and the service time becomes longer, it is particularly important to improve the mechanical properties and wear resistance, corrosion resistance, and weather resistance of the equipment surface, which can save a lot of property losses and avoid casualties. Among them, thermal spraying technology is a surface repair and protection technology that uses a specific heat source to heat the material to a molten or semi-molten state, and then deposits it on the surface of the substrate under the action of a carrier gas to eventually form a dense coating. It is widely used in engineering fields such as aerospace, shipbuilding, and automobiles. When high-energy plasma is used as the heat source for spraying, the temperature and speed of the flying molten droplets can reach "double highs", making it easier to obtain a denser and better-performing coating.

[0003] In the plasma spraying process, the temperature of the spray jet is significantly correlated with the melting degree of the feed and the final coating performance. To a certain extent, the higher the jet temperature, the better the melting degree of the flying molten droplets, and the denser the microstructure of the final coating. However, the cost of measuring the plasma spray jet by experimental means is high, and there are various errors in the measurement. Therefore, it is particularly important to use numerical simulation to study the temperature characteristics of the jet.

[0004] The existing method for simulating plasma spray jets is mainly to establish an electromagnetic continuity equation, give the model the boundary conditions at the corresponding anode and cathode, and apply gas ionization reaction to realize the calculation of the characteristics of the plasma jet. Among them, inside the plasma spray gun (plasma torch), the plasma energy density is high under high pressure and high temperature, and the electromagnetic effect is strong, which is suitable for solving using this method. As for the jet part in the air domain after flowing out of the spray gun outlet, most of them are aerodynamic problems rather than electromagnetic problems. Summary of the invention

[0005] The purpose of the present invention is to design and develop a plasma spray jet numerical simulation method based on an equivalent heat source model, obtain the jet characteristic distribution under different process parameters through numerical simulation, and reduce the experimental cost of monitoring the plasma jet.

[0006] The technical solution provided by the present invention is:

[0007] A plasma spray jet numerical simulation method based on an equivalent heat source model comprises the following steps:

[0008] Step 1: Use ANSYS SCDM software to establish the physical model of the internal channel and air domain of the spray gun and determine the calculation domain;

[0009] Step 2: Use Ansys Mesh to divide the mesh of the physical model and perform local encryption processing on the inner wall and outlet of the spray gun;

[0010] Step 3: Import the mesh into ANSYS Fluent, set the model to a two-dimensional axisymmetric form, couple the turbulence model, energy model and component transport model, and calculate the Navier-Stokes equations of mass, energy and momentum;

[0011] Step 4: In the computational domain, use UDF to introduce an equivalent heat source and solve the energy equation coupled to the NS.

[0012] Step 5: Apply boundary conditions to the model and add different equivalent heat source conditions;

[0013] Step 6: Use the SIMPLE algorithm, adopt the first-order upwind format, and after standard initialization, start the transient calculation with a step size of 10 μs until convergence;

[0014] Step 7: Use the post-processing software Tecplot to process the calculation results of the jet characteristics and obtain the simulated jet axial temperature results.

[0015] Preferably, the turbulence model is the SST k-omega turbulence model;

[0016] The component transport model includes three components: air, argon and hydrogen.

[0017] Preferably, the equivalent heat source can be added in the spray gun or in the air domain, corresponding to the heat generation of the plasma non-transferred arc and the transferred arc root respectively.

[0018] Preferably, the boundary conditions are mass flow rate at the inlet, component ratio, pressure outlet and adiabatic wall conditions.

[0019] Preferably, the heat generation of the equivalent heat source follows a Gaussian heat source distribution:

[0020]

[0021] The beneficial effects of the present invention are:

[0022] The present invention designs and develops a plasma spray jet numerical simulation method based on an equivalent heat source model, which obtains the jet characteristic distribution under different process parameters through numerical simulation, unifies the calculation process of the non-transferred arc mode and the transferred arc mode, and the simulation values ​​are basically consistent with the experimental values, thereby reducing the experimental cost of monitoring the plasma jet and laying a foundation for simply obtaining the jet characteristic distribution under different process parameters. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a schematic diagram of the real model structure of the plasma spraying gun of the present invention.

[0024] Figure 2 A schematic diagram of the position of the physical model and equivalent heat source can be added to the physical model of the present invention.

[0025] Figure 3 This is a jet temperature cloud map distribution diagram of Example 1 described in the present invention.

[0026] Figure 4 This is a jet temperature cloud map distribution diagram of Example 2 described in the present invention.

[0027] Figure 5 It is a jet axial temperature curve diagram of Example 1 and Example 2 described in the present invention.

[0028] Figure 6 It is a schematic diagram of the jet axial temperature verification curve of Example 2 described in the present invention. DETAILED DESCRIPTION

[0029] The present invention is further described in detail below so that those skilled in the art can implement it according to the description.

[0030] The present invention provides a plasma spray jet numerical simulation method based on an equivalent heat source model, comprising the following steps:

[0031] Step 1: Figure 1 As shown, according to the real model of the spray gun, the physical model of the internal channel and air domain of the spray gun is established using ANSYS SCDM software to determine the calculation domain;

[0032] Among them, the spray gun domain and air domain are determined by collecting the size of the spray gun, and then the calculation domain is obtained;

[0033] Step 2: Use Ansys Mesh to divide the mesh of the physical model and perform local encryption processing on the inner wall and outlet of the spray gun;

[0034] Step 3: Import the mesh into ANSYS Fluent, set the model to two-dimensional axisymmetric form, couple the turbulence model, energy model, and species transport model, and perform the calculation of the Navier-Stokes equations for mass, energy, and momentum;

[0035] Among them, the SST k-omega model is used for the turbulence model; the species transport model includes three species: air, argon, and hydrogen, and the plasma transport parameters are used to replace their thermodynamic parameters.

[0036] Step 4: As shown in Figure 2 , in the computational domain, use UDF to introduce an equivalent heat source and couple it with the energy equation in N-S for solution;

[0037] Among them, the position of the equivalent heat source can be added inside the spray gun and in the air domain, corresponding to the heat generation of the non-transferred plasma arc and the transferred arc root respectively;

[0038] The heat generation follows the Gaussian heat source distribution:

[0039]

[0040] In the formula, η is the spraying efficiency; P is the spraying power; R x , R y are the half-length and short-axis length of the heat source;

[0041] Step 5: Apply boundary conditions to the model and add different equivalent heat source conditions;

[0042] Among them, the boundary conditions of the model use the mass flow rate inlet, pressure outlet, and adiabatic wall conditions; according to different process parameters, appropriate mass flow rate and species ratio are added at the inlet, and the heat source conditions are changed.

[0043] Step 6: Use the SIMPLE algorithm, adopt the first-order upwind scheme, after standard initialization, under the condition of a time step of 10 μs, start the transient calculation until convergence;

[0044] Step 7: Use the post-processing software Tecplot to process the calculation results of the jet characteristics and obtain the simulated axial temperature results of the jet.

[0045] Example 1

[0046] During spraying, there is only one equivalent heat source and it is located in the spray gun. Spraying is carried out in a non-transferred arc mode, and the center of the non-transferred arc heat source is located on the axis and 2 mm away from the cathode tip. During spraying, the argon flow rate and the hydrogen flow rate are 90 slpm and 10 slpm, respectively. The volume molar ratios of the components at the inlet are 0.9 and 0.1, respectively, and the total mass flow rate is 0.0027 kg / s. The working power during spraying is the total power supplied to the non-transferred arc heat source in the spray gun, which is 40 kW. The efficiency of the non-transferred arc heat source is set to 50%, and the ratio of the major and minor axis lengths is 1.

[0047] Example 2

[0048] There are two equivalent heat sources during spraying, which are located in the spray gun and in the air domain respectively. The spraying is carried out in a combined arc mode. The center of the non-transferred arc heat source is located in the gun, 2 mm away from the cathode tip, and the center of the transferred arc heat source is located on the axis of the air domain, 10 mm away from the spray gun outlet. During spraying, the argon flow rate and the hydrogen flow rate are 120 slpm and 15 slpm respectively, the volume molar ratios of the components at the inlet are 0.888 and 0.112 respectively, and the total mass flow rate is 0.0036 kg / s. The working power during spraying is the sum of the non-transferred arc heat source power supplied to the gun and the transferred arc power outside the gun, wherein the non-transferred arc heat source power in the gun is 12 kW, the efficiency is set to 50%, and the ratio of the major and minor axis lengths is 1, wherein the transferred arc heat source power in the air domain outside the gun is 60 kW, the efficiency is set to 30%, and the ratio of the major and minor axis lengths is 1.

[0049] The jet axial temperature results are compared with the existing test results to complete the numerical simulation of the plasma spray jet based on the equivalent heat source model:

[0050] The calculation results of jet characteristics are processed using the post-processing software Tecplot, such as Figure 3-Figure 5 As shown, in Example 1, the jet temperature field is calculated to be stable under transient conditions, and the maximum value of the jet temperature is about 12000K; in Example 2, the jet temperature field is calculated to be stable under transient conditions, and the maximum values ​​of the jet temperature are about 6000K and 9000K; the jet axial temperature results are compared with the existing test results. Figure 6 As shown, the temperature distribution in the axial direction of the jet is measured using a fiber optic spectrometer, and the numerical simulation of the plasma spray jet based on the equivalent heat source model is completed. The results show that the calculated value of the jet axial temperature is in good agreement with the experimental value.

[0051] The present invention designs and develops a plasma spray jet numerical simulation method based on an equivalent heat source model, adjusts the equivalent heat source conditions and process parameters in the model, obtains the jet characteristic distribution under different process parameters by numerical simulation, and can complete experimental verification, unifies the calculation process of the non-transferred arc mode and the transferred arc mode, and the simulation values ​​are basically consistent with the experimental values, which reduces the experimental cost of monitoring the plasma jet and lays a foundation for simply obtaining the jet characteristic distribution under different process parameters.

[0052] Although the embodiments of the present invention have been disclosed as above, they are not limited to the applications listed in the specification and the implementation modes. They can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present invention is not limited to the specific details and the embodiments shown and described herein.

Claims

1. A plasma spray jet numerical simulation method based on an equivalent heat source model, characterized in that: The steps include: Step 1: Use ANSYS SCDM software to establish the physical model of the internal channel and air domain of the spray gun and determine the calculation domain; Step 2: Use Ansys Mesh to divide the mesh of the physical model and perform local encryption processing on the inner wall and outlet of the spray gun; Step 3: Import the mesh into ANSYS Fluent, set the model to a two-dimensional axisymmetric form, couple the turbulence model, energy model and component transport model, and calculate the Navier-Stokes equations of mass, energy and momentum; Step 4: In the computational domain, use UDF to introduce an equivalent heat source and solve the energy equation coupled to the NS. Step 5: Apply boundary conditions to the model and add different equivalent heat source conditions; Step 6: Use the SIMPLE algorithm, adopt the first-order upwind format, and after standard initialization, start the transient calculation with a step size of 10 μs until convergence; Step 7: Use the post-processing software Tecplot to process the calculation results of the jet characteristics and obtain the simulated jet axial temperature results.

2. The plasma spray jet numerical simulation method based on the equivalent heat source model according to claim 1, characterized in that: The turbulence model is the SST k-omega turbulence model; The component transport model includes three components: air, argon and hydrogen.

3. The plasma spray jet numerical simulation method based on the equivalent heat source model according to claim 2, characterized in that: The equivalent heat source can be added in the spray gun or in the air domain, corresponding to the heat generation of the plasma non-transferred arc and the transferred arc root respectively.

4. The plasma spray jet numerical simulation method based on the equivalent heat source model according to claim 3, characterized in that: The boundary conditions are mass flow rate at the inlet, component ratio, pressure outlet and adiabatic wall conditions.

5. The plasma spray jet numerical simulation method based on the equivalent heat source model according to claim 4, characterized in that: The heat generation of the equivalent heat source follows the Gaussian heat source distribution: Where, η is the spraying efficiency; P is the spraying power; R x , R y It is the half length and minor axis length of the heat source.

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