Simulation method for three-dimensional distribution of gas switch discharge ablation particles

Abstract

The invention relates to a gas switch discharge ablation particle diffusion simulation method, in particular to a gas switch discharge ablation particle three-dimensional distribution simulation method, and aims to solve the technical problem that the existing gas spark gas switch discharge ablation particle motion law cannot be directly measured. The invention relates to a gas switch discharge ablation particle three-dimensional distribution simulation method, which comprises the following steps: 1) establishing a gas switch three-dimensional simulation model, and obtaining a calculation area and a discharge channel; 2) calculating the injection energy density of the discharge channel; 3) setting a control equation according to the injection energy density; calculating the position distribution of ablated particles by using a control equation; the position distribution comprises a movement speed and a movement direction; 4, ablative particles are arranged in the calculation area, and distribution of the ablative particles in the gas switch is obtained, and 5, boundary conditions of the calculation area are set, and simulation of three-dimensional distribution of the gas switch discharge ablative particles is completed.

Description

Technical Field

[0001] The present invention relates to a simulation method for the diffusion of ablation particles in a gas switch discharge, and specifically to a simulation method for the three-dimensional distribution of ablation particles in a gas switch discharge. Background Art

[0002] In recent years, pulsed power technology has developed rapidly and has been widely applied in more and more new fields. Gas spark switches have been widely used since the initial stage of the development of pulsed power technology. The conduction of a gas switch is accompanied by spark and arc discharges. The formed plasma channel has a high temperature and a large current density, which will cause ablation of the electrode surface. After multiple discharges, the evaporation and splashing of the electrode ablation products will lead to electrode damage, environmental pollution inside the gas spark switch, and deterioration of the insulating medium, thus affecting the safe and stable operation of the pulsed power equipment.

[0003] Existing research on electrode ablation can be divided into two aspects: on the one hand, it includes theoretical research and experimental research on electrode ablation; the theoretical research on electrode ablation includes ablation mechanisms and simulation models; the experimental research on electrode ablation includes research on ablation influencing factors and electrode materials. On the other hand, the formation of the discharge channel is accompanied by energy injection, generating a high-temperature and high-pressure region, which will cause gas expansion. As a result, the ablation particles generated during the discharge process of the gas spark switch will inevitably diffuse to the inner wall of the gas spark switch along with the gas expansion. Adhering to the inner wall surface will reduce the surface insulation performance of the inner wall, resulting in surface flashover inside the gas spark switch and affecting the service life of the gas spark switch. Since the ablation particles are small, it is difficult to conduct experimental measurements. Simulating the diffusion movement process of ablation particles inside the gas spark switch through simulation calculation is an effective method for studying the movement law of ablation particles. However, there is still a lack of relevant research at present. Summary of the Invention

[0004] The purpose of the present invention is to solve the technical problem that the movement law of ablation particles in the existing gas spark switch discharge cannot be directly measured, and to provide a simulation method for the three-dimensional distribution of ablation particles in a gas switch discharge, providing support for mastering the three-dimensional diffusion and distribution law of ablation particles in a gas switch discharge.

[0005] In order to achieve the above purpose, the present invention adopts the following technical solutions:

[0006] A simulation method for the three-dimensional distribution of ablation particles in a gas switch discharge, characterized in that it includes the following steps:

[0007] 1. Establish a three-dimensional simulation model of the gas switch to obtain the calculation area and the discharge channel;

[0008] 2. Calculate the injection energy density of the discharge channel;

[0009] 3】Set the control equations according to the injection energy density; calculate the position distribution of the ablation particles using the control equations; the position distribution includes the movement speed and movement direction;

[0010] 4】Set ablation particles in the calculation region to obtain the distribution of ablation particles in the gas switch;

[0011] 5】Set the boundary conditions of the calculation region to complete the simulation of the three-dimensional distribution of ablation particles during gas switch discharge.

[0012] Further, step 1】is specifically as follows:

[0013] 1.1. In the ablation particle diffusion process simulation software, set the pressure and temperature inside the gas switch;

[0014] 1.2. According to the physical structure of the gas switch, take the non-solid space region inside the gas switch as the calculation region, and based on the principle that the probability of discharge at the point with the maximum field strength is the highest and the ultraviolet pre-ionization principle according to the discharge position in the actual working process, complete the establishment of the three-dimensional simulation model of the gas switch.

[0015] Further, step 2】is specifically as follows:

[0016] Take the discharge channel as the energy injection region, inject energy into the discharge channel to simulate the heating of the gas by the arc, and calculate the injection energy density Q of the discharge channel through the following formula:

[0017]

[0018] In the formula, E is the deposited energy of the discharge channel; η is the gas heating efficiency in the gas switch; V is the volume of the discharge channel; t is the time of injecting energy.

[0019] Further, in step 3】, the control equations are the Navier-Stokes equations:

[0020]

[0021] In the formula, ρ represents the gas density, represents the gas velocity, represents the gas stress tensor, represents the external volume force source term, e represents the total gas energy, p represents the gas pressure, k T represents the gas thermal conductivity, T represents the gas temperature, represents taking the gradient.

[0022] Further, step 4】is specifically as follows:

[0023] Set ablation particles in the computational domain; obtain the distribution of ablation particles in the gas switch according to the Rosin-Rammler distribution:

[0024]

[0025] where Y d represents the mass fraction of ablation particles with a diameter of d, is the average particle size of the ablation particles, and n is the size distribution index, where n > 1.

[0026] Furthermore, in step 5, the boundary condition is to set the inner wall of the gas switch as a no-slip wall surface, and its inlet and outlet are set as no-slip wall surfaces during the discharge of the gas switch.

[0027] Advantages of the present invention:

[0028] 1. The simulation method for the three-dimensional distribution of ablation particles during the discharge of a gas switch in the present invention provides theoretical support for improving the working reliability and service life of a gas spark switch, and provides support for mastering the three-dimensional diffusion law and distribution of ablation particles during the discharge of a gas switch.

[0029] 2. The simulation method for the three-dimensional distribution of ablation particles during the discharge of a gas switch in the present invention can not only simulate the process of ablation particles diffusing with gas collisions in a gas switch, but also simulate the process of ablation particles moving and diffusing under the action of gas flow in various pulse power devices. Description of the drawings

[0030] Figure 1 is a flowchart of an embodiment of the simulation method for the three-dimensional distribution of ablation particles during the discharge of a gas switch in the present invention;

[0031] Figure 2 is a schematic diagram of a simulation model for setting ablation particles in an embodiment of the simulation method for the three-dimensional distribution of ablation particles during the discharge of a gas switch in the present invention, where blue represents ablation particles;

[0032] Figures 3(a) to 3(j) are respectively schematic diagrams of the movement trajectory simulations of ablation particles at 1 μs, 6 μs, 22 μs, 50 μs, 90 μs, 210 μs, 650 μs, 1 ms, 1.8 ms, and 16 ms after the breakdown discharge of the gas switch in an embodiment of the simulation method for the three-dimensional distribution of ablation particles during the discharge of a gas switch. Detailed implementation manners

[0033] As Figure 1 shown, a simulation method for the three-dimensional distribution of ablation particles during the discharge of a gas switch, aiming at the gas switch in a pulse power device, includes the following steps:

[0034] 1】Establish a three-dimensional simulation model of the gas switch:

[0035] 1.1. In the ablation particle diffusion process simulation software, set the pressure and temperature inside the gas switch; in this embodiment, the pressure is the actual working pressure of the gas switch, 6.5 bar, and the temperature is the initial temperature of 300 K.

[0036] 1.2. According to the physical structure of the gas switch, take the non-solid space area inside the gas switch as the calculation area, and based on the principle that the probability of discharge at the point with the maximum field strength is the highest during the actual working process and the principle of ultraviolet pre-ionization, complete the establishment of the three-dimensional simulation model of the gas switch.

[0037] 2】Calculate the injection energy density Q of the discharge channel of the gas switch:

[0038] According to the actual working process of the gas switch, after the gas switch conducts and discharges, the energy is deposited in the discharge channel, forming a high-temperature and high-pressure area. The pressure difference between it and the surrounding area causes the gas to flow rapidly around and drives the ablation particles to move accordingly. In the three-dimensional simulation model of the gas switch, take the discharge channel as the energy injection area and inject energy into the discharge channel to simulate the heating of the gas by the arc.

[0039] Calculate the injection energy density Q through the following formula:

[0040]

[0041] In the formula, E is the deposited energy of the discharge channel, which is about 40 - 50% of the energy released by the capacitor during the breakdown discharge process of the gas switch; η is the gas heating efficiency in the gas switch, and the efficiency of converting the energy released by the capacitor into heat energy is generally 10 - 20%; V is the volume of the discharge channel; t is the time of injecting energy, and according to the current waveform, the value is 400 ns.

[0042] In this embodiment, according to the working voltage of ±80 kV of the gas switch, it can be calculated that the energy density Q of the discharge channel of the gas switch is 5×10 14 W / m 3 ~10×10 14 W / m 3 .

[0043] 3】Set the control equations according to the injection energy density Q obtained in step 2】; use the control equations to calculate the position distribution of the ablation particles during the process of gas molecule movement and the interaction between gas molecules and ablation particles, and the position distribution includes the movement speed and movement direction.

[0044] In this embodiment, the control equations are the Navier-Stokes equations with an energy source term. Preferably, when considering the thermodynamic multi-temperature model, the corresponding energy conservation equation in the corresponding energy mode should also be considered. The Navier-Stokes equations are as follows:

[0045]

[0046] where ρ represents the gas density, represents the gas velocity, represents the gas stress tensor, represents the external volume force source term, e represents the total gas energy, p represents the gas pressure, k T represents the gas thermal conductivity, T represents the gas temperature, represents the gradient;

[0047] Calculate the gas stress tensor in formula (2) according to formula (4)

[0048]

[0049] where μ represents the dynamic viscosity, T’ represents the transpose symbol, represents the identity matrix.

[0050] Calculate the total gas energy e in formula (3) according to formulas (5), (6), and (7):

[0051] e = e i + e k (5)

[0052]

[0053] where e i is the internal energy, e k is the kinetic energy, h represents the enthalpy;

[0054] Calculate the gas thermal conductivity k in formula (3) according to formulas (8), (9), and (10) T and the dynamic viscosity μ and the specific heat capacity c of the gas in formula (4) p,i :

[0055]

[0056] where R is the gas constant, M i is the molecular weight of component i, σ is the collision diameter of gas molecules and ablation particles, Ω is the collision integral, f i is the degree of freedom of component i, i = 1, 2,..; the components are gas molecules and ablation particles;

[0057] 4】Set ablation particles in the computational domain to obtain the distribution of ablation particles within the gas switch:

[0058] As Figure 2 shown, set a certain number of ablation particles in the computational domain as the object of simulation study. The gas movement drives the movement of ablation particles, and the particle size and mass fraction of ablation particles follow the Rosin-Rammler distribution:

[0059]

[0060] In the formula, Y d represents the mass fraction of ablation particles with a diameter of d, is the average particle size of ablation particles, and n is the size distribution index, which is set to 1.5 in the simulation;

[0061] 5】Set the boundary conditions of the computational domain:

[0062] Except for the energy injection in the discharge channel area, other areas are free-flow spaces. Therefore, the boundary condition is to set the inner wall of the gas switch as a non-slip wall surface, and its inlet and outlet are set as non-slip wall surfaces during the discharge of the gas switch, completing the simulation of the three-dimensional distribution of ablation particles during the discharge ablation of the gas switch.

[0063] In the pulsed power device, the gas switch discharge is completed on the nanosecond time scale. Subsequently, the ablation particles begin to diffuse with the gas expansion, and the duration is about on the millisecond scale. According to the principle that the discharge probability is the highest at the point with the maximum field strength and the principle of ultraviolet pre-ionization, determine the discharge channel position and inject a certain amount of energy. In the area near the discharge point, set a certain number of microparticles to simulate ablation particles, and the injected energy is calculated based on the energy stored in the capacitor, simulating the diffusion process of ablation particles with the air expansion.

[0064] After the gas switch discharges, the movement process of ablation particles inside the gas switch is mainly that the gas collision drives the movement of ablation particles. Therefore, it includes two phases: gas phase and solid phase. During the simulation process, the ablation particles are regarded as small solid particles, moving with the gas collision, and their content is very small. The volume content of the solid phase in the total volume is much lower than 15%.

[0065] The governing equations for the computational simulation are the Navier-Stokes equations with an energy source term. The entire simulation process involves the gas phase and the solid phase. Among them, the ablated particles of the solid phase are regarded as the discrete phase, and the mass and volume of the ablated particles during each discharge of the gas switch are extremely small, so the interaction forces between particles are not considered. After the discharge, the pressure and temperature in the discharge channel will increase sharply, forming a pressure difference with the surrounding area, which causes the gas in the discharge channel to expand violently. Due to the complex internal structure of the gas switch, turbulence will form in some areas of the fluid. The discrete-phase particles and the fluid-phase gas exchange momentum and energy with each other. In order to obtain the distribution of ablated particles at different times, different time steps need to be set for calculation. In this embodiment, the time step of the calculation iteration is set in segments. During the energy injection process of simulating the discharge of the gas switch, since the change gradients of pressure and temperature with time are extremely large, the time step is set as small as possible, set to 10 ns, and 40 time steps are calculated, with each time step iterated 10 times. After the energy injection, the change gradients of pressure and temperature gradually decrease, and the time step gradually increases to reduce the calculation duration.

[0066] When the energy density in the discharge channel is 7.5×10 14 W / m 3 , and the internal air pressure of the gas switch is 6.5 bar, after the gas switch discharges, the movement process of the ablated particles along with the internal gas flow of the gas switch is as Figures 3(a) to 3(j) shown, where the particles of different colors represent ablated particles of different diameters; it can be seen from the simulation schematic diagrams of the movement trajectories of the ablated particles at 1 μs, 6 μs, 22 μs, 50 μs, 90 μs, 210 μs, 650 μs, 1 ms, 1.8 ms, and 16 ms after the gas switch breaks down and discharges that the diffusion speed of the ablated particles after the discharge is extremely fast, and they have diffused to the inner wall of the gas switch at 650 μs, presenting an overall spherical diffusion form; when the ablated particles diffuse along the z direction to the inner wall of the gas switch, they move and diffuse along the wall surface to both sides in the y direction under the constraint of the wall surface; at 16 ms, since the pressure inside the gas switch is basically stable and the gas flow velocity becomes extremely small, the movement speed of the ablated particles also becomes extremely slow.

Claims

1. A method for simulating the three-dimensional distribution of gas switch discharge ablation particles, characterized in that: The following steps are involved: 1] Establish a three-dimensional simulation model of the gas switch to obtain the calculation area and discharge channel; 2] Calculate the injection energy density of the discharge channel; 3] Setting a control equation according to the injected energy density; calculating the position distribution of the ablated particles using the control equation; the position distribution includes the movement speed and the movement direction; 4] Set ablation particles in the calculation area to obtain the distribution of ablation particles in the gas switch; 5] Set the boundary conditions of the calculation area to complete the simulation of the three-dimensional distribution of gas switch discharge ablation particles.

2. According to claim 1, a method for simulating the three-dimensional distribution of gas switch discharge ablation particles is characterized in that: Step 1] Specifically: 1.

1. In the ablation particle diffusion process simulation software, set the pressure and temperature inside the gas switch; 1.

2. According to the physical structure of the gas switch, the non-solid space area inside the gas switch is used as the calculation area, and the discharge channel is separated according to the discharge position in the actual working process based on the principle of maximum discharge probability at the point of maximum field strength and the principle of ultraviolet pre-ionization to complete the establishment of the three-dimensional simulation model of the gas switch.

3. The method for simulating the three-dimensional distribution of discharge ablation particles in a gas switch according to claim 2, characterized in that: Step 2] Specifically: The discharge channel is taken as the energy injection area, and energy is injected into the discharge channel to simulate the arc heating of the gas. The injected energy density Q of the discharge channel is calculated by the following formula: Where E is the deposition energy of the discharge channel; η is the gas heating efficiency in the gas switch; V is the volume of the discharge channel; and t is the time for injecting energy.

4. The method for simulating the three-dimensional distribution of discharge ablation particles in a gas switch according to claim 3, characterized in that: In step 3], the control equation is the Navier-Stokes equations: In the formula, ρ represents the gas density, is the gas velocity, represents the gas stress tensor, represents the external volume force source term, e represents the total energy of the gas, p represents the gas pressure, k T represents the thermal conductivity of the gas, T represents the gas temperature, It means to find the gradient.

5. The method for simulating the three-dimensional distribution of discharge ablation particles in a gas switch according to claim 4, characterized in that: Step 4] Specifically: Set the ablation particles in the calculation area; obtain the distribution of the ablation particles in the gas switch according to the Rosin-Rammler distribution: Among them, Y d represents the mass fraction of ablated particles with diameter d, is the average particle size of the ablated particles, n is the size distribution index, and n>

1.

6. The method for simulating the three-dimensional distribution of discharge ablation particles in a gas switch according to claim 5, characterized in that: In step 5], the boundary condition is to set the inner wall of the gas switch as a no-slip wall, and its air inlet and air outlet are set as no-slip walls when the gas switch is discharging.

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