One-dimensional Fluid Simulation Research Articles

Fluid simulations for a finite size plasma

Studies on finite-size plasma have attracted a lot of attention lately. They can form by ionizing liquid droplets by lasers. The dynamical behavior of such plasma droplets is, therefore, a topic of significant interest. In particular, questions related to the linear and nonlinear characteristics (associated with the inhomogeneous density typically at the edge of the droplet), the behavior of plasma expansion, etc., are of interest. A one-dimensional fluid simulation study has been carried out to investigate this behavior. It is observed that a slight imbalance in the charge density leads to oscillations that are concentrated and keep acquiring higher amplitude and sharper profiles at the inhomogeneous edge region. Such oscillations lead to the expansion of the droplet. Though the fluid description breaks when the sharpness of these structures becomes comparable to the grid size, it provides a reasonable estimate of wave-breaking time. The presence of dissipative effects such as diffusion is shown to arrest the sharpness of these structures. The dynamics of these structures in the presence of an externally applied oscillating electric field corresponding to long wavelength radiation have also been studied.

Driven ion acoustic wave nonlinearities in superthermal electron plasmas

The fluid nonlinearities of driven ion acoustic waves (IAWs) in superthermal electron plasmas are investigated by fluid theory and one-dimensional fluid simulation. A kappa velocity distribution function is used to model superthermal electrons. Under the condition of small wave amplitudes, simulation results are presented to verify the conclusion of fluid theory, showing that the presence of superthermal electrons leads to stronger harmonic generation and larger nonlinear frequency shifts of IAWs. In addition, the growth rate and threshold of the IAW decay instability from simulations are well predicted by a simple three-wave fluid theory. It is shown that the nonlinear frequency shift has a significant effect on IAW decay, and for a larger population of superthermal electrons, the IAW decay has a smaller onset threshold and threshold range.

Effect of the inertial term of the ion momentum equation on fluid transport simulation for capacitively coupled plasma sources

Fluid-based simulations are widely used to analyze or optimize capacitively coupled plasma sources. Although the inertial term of the ion momentum equation affects the accuracy of the solutions, the equation has not been considered in the drift-diffusion approximation model in the numerical solution. Therefore, we, herein, improved the accuracy of the model by applying an effective electric field, considering the inertial term. First, the effective electric field, including the ion inertial term of the ion momentum equation, was derived. Subsequently, one-dimensional fluid simulations were conducted. The numerical results were compared with those of one-dimensional particle-in-cell (PIC) simulations. The results of the developed model were similar to those obtained in the case of solving the full-ion momentum equation, as well as more similar to the PIC simulation results than those obtained in the case of the drift-diffusion approximation.

Investigating the effects of helium, argon and hydrogen co-feeding on the non-oxidative coupling of methane in a dielectric barrier discharge reactor

The impact of helium, argon, and hydrogen co-feeding on methane non-oxidative coupling in dielectric barrier discharges is investigated in terms of reaction pathways and energy efficiency. One-dimensional fluid simulations are used to investigate short time-scales. Zero-dimensional global modelling, using inputs from the one-dimensional simulations, is utilised to study time-scales equivalent to those of experimental reactors. A previously developed detailed kinetic scheme for non-thermal methane plasma that accounts for the reactivity and relaxation of electronically and vibrationally excited species is extended to describe the interactions of noble gases with the species within the methane plasma. A wide range of compositions and applied voltages are studied to determine the conditions that improve the energy efficiency of methane conversion and the selectivity to value-added products. Penning dissociation has a significant impact in the case of mixtures with high content of argon, while hydrogen co-feeding increases selectivity towards ethane and ethylene versus acetylene.

Numerical simulation of discharge mode conversion with multiple current pulse (MCP) in atmospheric pressure He/N2 dielectric barrier discharge

A one-dimensional fluid simulation model of He/N2 dielectric barrier discharge with parallel plate electrodes was established to study the effects of different parameters (such as gap width, secondary electron emission coefficient γ, and driven frequency) on the characteristics of multiple current pulse (MCP) discharge and the discharge mode conversion. The discharge can be divided into Townsend discharge, transition state, and glow discharge. The results show that with the increase in γ, the number of discharge current pulses increases, making it more difficult to form a glow discharge. When γ is larger, the first discharge approaches the glow discharge mode, but the positive column region is not completely formed, and the subsequent discharge sequence undergoes a transition state to Townsend discharge gradually. Under the condition of larger γ, MCP discharge with a short gap is Townsend discharge. With the increase in the gap width, the transition state will appear in the first discharge, and the subsequent discharge sequence may be converted into Townsend discharge. When the gap width increases further, the discharge can be completely transformed into glow discharge. The pulse number of discharge current decreases with the increase in frequency, and the higher frequency is conducive to the formation of glow discharge.

Generation of series of electron acoustic solitary wave pulses in plasma

One-dimensional fluid simulation is used to investigate the generation of electron-acoustic solitary waves (EASWs) in three-species plasma. We consider an unmagnetized collisionless plasma consisting of cold electrons, hot electrons, and ions. The Gaussian perturbations in the equilibrium electron and ion densities are used to excite the waves in the plasma. This simulation demonstrates the generation of a series of EASW pulses in this three-species plasma through the process of wave breaking. We investigate the behavior of the ponderomotive potential, frequency, and force associated with electrons and ions during the process of the wave breaking. We observed that the ponderomotive potential of the hot electron, which is the driving species for the electron acoustic waves, peaks at the time of wave breaking. The variation of the maximum ponderomotive force acting spatially on the leading and trailing edges of the hump in the cold and hot electron and ion fluid densities shows the maximum imbalance in the magnitude of the ponderomotive force acting on both sides of the hot electron density hump at the time of wave breaking. This reveals that the imbalanced ponderomotive force acting on the hot electron fluid is responsible for the breaking of the electron acoustic wave in plasma. Furthermore, it is observed that the wave breaking process occurs at an earlier time if the hot electron temperature is increased.

Comparison between ad-hoc and instability-induced electron anomalous transport in a 1D fluid simulation of Hall-effect thruster

Anomalous electron transport is a long-standing problem in the understanding of Hall-effect thrusters. Recent results have suggested as a possible cause a kinetic instability, but few attempts have succeeded in implementing such phenomena in a fluid simulation of the thruster. The common approach in this case relies on including an ad-hoc model of the anomalous transport and so to fit experimental results. We propose here a comparison between the friction force and the anomalous heating arising from the ad-hoc model, with the corresponding effects coming from the use of the instability-induced transport. The results are obtained through a one-dimensional fluid simulation of the Hall-effect thruster with ad-hoc anomalous transport. The comparison shows good agreement between the two approaches, suggesting indeed that the instability-induced anomalous transport is the good candidate for reproducing the ad-hoc simulations and paving the way for a full self-consistent implementation of the phenomena in a fluid simulation.

Effects of secondary electron emission on plasma characteristics in dual-frequency atmospheric pressure helium discharge by fluid modeling**Project supported by the National Natural Science Foundation of China (Grant No. 11505089).

A one-dimensional (1D) fluid simulation of dual frequency discharge in helium gas at atmospheric pressure is carried out to investigate the role of the secondary electron emission on the surfaces of the electrodes. In the simulation, electrons, ions of He+ and , metastable atoms of He* and metastable molecules of are included. It is found that the secondary electron emission coefficient significantly influences plasma density and electric field as well as electron heating mechanisms and ionization rate. The particle densities increase with increasing SEE coefficient from 0 to 0.3 as well as the sheathʼs electric field and electron source. Moreover, the SEE coefficient also influences the electron heating mechanism and electron power dissipation in the plasma and both of them increase with increasing SEE coefficient within the range from 0 to 0.3 as a result of increasing of electron density.

Simulation Calculation of Flow Characteristics of Air Separation System Based on Flowmaster

The air separation system is an important part of aircraft fuel inerting system, which is responsible for the important task of supplying nitrogen-enriched air to the aircraft fuel tank. The flow characteristic of air separation device is the key problem of its design. In this paper, based on one-dimensional fluid simulation software Flowmaster, we did some research on the simulation model of membrane modules, established the simulation model of air separation system, obtained the simulation results of the flow characteristics and analyzed the results in detail. The results showed that under low pressure and flow conditions, compared with the experimental values, the relative error of nitrogen-enriched air and oxygen-enriched air flow rate was about 5%.In the case of high inlet pressure and flow, the pressure loss of the junctions and the long pipeline was larger, and the inlet pressure, outlet pressure and pressure loss of the 12 membrane modules were significantly different. The research work was of reference value for the design optimization of air separation system in aircraft fuel inerting system.

A one-dimensional fluid simulation method of branching narrow vessel for real-time angiography simulation.

This paper proposes a one-dimensional fluid simulation method for real-time simulation of the contrast medium in a narrow blood vessel. A narrow vessel is modeled with the branches organized in a hierarchy. The density of the contrast medium on each branch is computed using the one-dimensional fluid model. The density at the last point of branch is conveyed to the first point of the following branches. The position of the density computation is determined to continuously convey the simulation results from a large vessel to a narrow vessel. The average computation time with the proposed method is 16.18 ms that is less than 21.25 ms of the particle-based method.

A parallelization method for time periodic steady state in simulation of radio frequency sheath dynamics

In order to reduce the computing time in simulation of radio frequency (rf) plasma sources, various numerical schemes were developed. It is well known that the upwind, exponential, and power-law schemes can efficiently overcome the limitation on the grid size for fluid transport simulations of high density plasma discharges. Also, the semi-implicit method is a well-known numerical scheme to overcome on the simulation time step. However, despite remarkable advances in numerical techniques and computing power over the last few decades, efficient multi-dimensional modeling of low temperature plasma discharges has remained a considerable challenge. In particular, there was a difficulty on parallelization in time for the time periodic steady state problems such as capacitively coupled plasma discharges and rf sheath dynamics because values of plasma parameters in previous time step are used to calculate new values each time step. Therefore, we present a parallelization method for the time periodic steady state problems by using period-slices. In order to evaluate the efficiency of the developed method, one-dimensional fluid simulations are conducted for describing rf sheath dynamics. The result shows that speedup can be achieved by using a multithreading method.

浮动核电站给水系统瞬态分析

基于浮动核电站主给水系统，利用Flowmaster仿真软件建立了从除氧器出口至蒸汽发生器出口的给水系统模型。对给水系统四种瞬态过程中蒸汽发生器的水量变化进行分析：额定工况下一台给水泵跳闸，备用泵连锁启动；额定工况下一台给水泵跳闸，备用泵连锁启动失败；带零负荷时主给水调节阀故障全开；带满负荷时主给水调节阀故障全开。仿真结果表明，在给水泵切换瞬态工况下，蒸汽发生器的失水量在要求的范围内，不会触发反应堆跳停。并且根据瞬态工况的蒸汽发生器上水量的变化曲线，得到了保守的给水流量值作为核岛安全分析的输入，确保这些瞬态工况下堆芯不发生DNB。 Based on the floating nuclear power plant main water feeding system, the water feeding process model from the outlet of deaerator to the outlet of the steam generator is established by using a one-dimensional fluid simulation software Flowmaster. The change of water quantity of steam generator in four transient processes of water supply system is analyzed, includes: a water pump trip in rated state, and standby pump interlock start; a water pump trip in rated state, and standby pump interlock start; main feed-regulating valve is in full open due to failure under no load; main feed-regulating valve is in full open due to failure under full load. The simulation results show that: steam generator water level changes within the scope of the requirements under the feed pump switching transient conditions, which cannot trip the reactor. And according to steam generator water supply curves under the transient conditions, the conservative water flow value is obtained, which is an input to the nuclear island safety analysis, and to make sure the reactor core do not departure from nucleate boiling under these transient conditions.

Fluid simulation of dispersive and nondispersive ion acoustic waves in the presence of superthermal electrons

One-dimensional fluid simulation is performed for the unmagnetized plasma consisting of cold fluid ions and superthermal electrons. Such a plasma system supports the generation of ion acoustic (IA) waves. A standard Gaussian type perturbation is used in both electron and ion equilibrium densities to excite the IA waves. The evolutionary profiles of the IA waves are obtained by varying the superthermal index and the amplitude of the initial perturbation. This simulation demonstrates that the amplitude of the initial perturbation and the superthermal index play an important role in determining the time evolution and the characteristics of the generated IA waves. The initial density perturbation in the system creates charge separation that drives the finite electrostatic potential in the system. This electrostatic potential later evolves into the dispersive and nondispersive IA waves in the simulation system. The density perturbation with the amplitude smaller than 10% of the equilibrium plasma density evolves into the dispersive IA waves, whereas larger density perturbations evolve into both dispersive and nondispersive IA waves for lower and higher superthermal index. The dispersive IA waves are the IA oscillations that propagate with constant ion plasma frequency, whereas the nondispersive IA waves are the IA solitary pulses (termed as IA solitons in the stability region) that propagate with the constant wave speed. The characteristics of the stable nondispersive IA solitons are found to be consistent with the nonlinear fluid theory. To the best of our knowledge, this is the first fluid simulation study that has considered the superthermal distributions for the plasma species to model the electrostatic solitary waves.

Experimental evidence of ion acoustic soliton chain formation and validation of nonlinear fluid theory

We perform one-dimensional fluid simulation of ion acoustic (IA) solitons propagating parallel to the magnetic field in electron-ion plasmas by assuming a large system length. To model the initial density perturbations (IDP), we employ a KdV soliton type solution. Our simulation demonstrates that the generation mechanism of IA solitons depends on the wavelength of the IDP. The short wavelength IDP evolve into two oppositely propagating identical IA solitons, whereas the long wavelength IDP develop into two indistinguishable chains of multiple IA solitons through a wave breaking process. The wave breaking occurs close to the time when electrostatic energy exceeds half of the kinetic energy of the electron fluid. The wave breaking amplitude and time of its initiation are found to be dependent on characteristics of the IDP. The strength of the IDP controls the number of IA solitons in the solitary chains. The speed, width, and amplitude of IA solitons estimated during their stable propagation in the simulation are in good agreement with the nonlinear fluid theory. This fluid simulation is the first to confirm the validity of the general nonlinear fluid theory, which is widely used in the study of solitary waves in laboratory and space plasmas.

Observation of sharply peaked solitons in dusty plasma simulations

We report on observations of cusp-like sharply peaked dust acoustic solitons in a one-dimensional fluid simulation of a dusty plasma system. These nonlinear singular structures, dithering at the wave breaking point, are found to be long-lived entities that emerge spontaneously from a variety of large-amplitude initial perturbations. Such excitations can play a significant role in wave breaking and wave-particle dynamics in dusty plasmas and may explain some recent experimental observations.

Generation and loss of reactive oxygen species in low-temperature atmospheric-pressure RF He + O2 + H2O plasmas

This study focuses on the generation and loss of reactive oxygen species (ROS) in low-temperature atmospheric-pressure RF (13.56 MHz) He + O2 + H2O plasmas, which are of interest for many biomedical applications. These plasmas create cocktails of ROS containing ozone, singlet oxygen, atomic oxygen, hydroxyl radicals, hydrogen peroxide and hydroperoxyl radicals, i.e. ROS of great significance as recognized by the free-radical biology community. By means of one-dimensional fluid simulations (61 species, 878 reactions), the key ROS and their generation and loss mechanisms are identified as a function of the oxygen and water content in the feed gas. Identification of the main chemical pathways can guide the optimization of He + O2 + H2O plasmas for the production of particular ROS. It is found that for a given oxygen concentration, the presence of water in the feed gas decreases the net production of oxygen-derived ROS, while for a given water concentration, the presence of oxygen enhances the net production of water-derived ROS. Although most ROS can be generated in a wide range of oxygen and water admixtures, the chemical pathways leading to their generation change significantly as a function of the feed gas composition. Therefore, care must be taken when selecting reduced chemical sets to study these plasmas.

Fluid simulation of an electrostatic plasma sheath with two species of positive ions and charged nanoparticles

One-dimensional fluid simulations are used to study the dynamics of an electrostatic plasma sheath containing nanosized dust grains and two species of positive ions, i.e., He+ and Ar+. The impacts of the concentration of each species, the velocity at the sheath edge of the ions, and the bias voltage of the substrate, on the spatial distribution of the velocity and number density of the plasma particles, and the incident fluxes of the ions on the substrate, are investigated. The numerical results show that the sheath thickness increases with increasing σ, the density ratio of He+ ions to Ar+ ions at the sheath edge. For nanosized dust particles considered in this work, the dominant forces are the ion drag and the electric force and the effects of the neutral drag and gravity are negligible. Due to enhancement of the ion drag force and the electric force, the dust velocity increases and, consequently, the dust number density decreases as the concentration at the sheath edge of Ar+ ions is increased. For the same velocity and number density at the sheath edge, the number density of Ar+ ions near the wall is larger than that of He+ ions, but their incident fluxes are the same. The maximum in the dust number density increases with the velocity of Ar+ ions at the sheath edge, but it weakly changes with the Mach number of He+ ions, except for large values of σ. The position of the maximum dust number density initially decreases very quickly with increasing the velocity at the sheath edge of the ions from small values, but then at larger values it changes quite slowly. The differences in the sheath parameters for different values of σ disappear at some values of the velocity at the sheath edge of the ions and dust particles. The incident flux of the ions are independent of the bias voltage of the substrate, but their kinetic energy is equal to the bias potential.

Effect of high Xe-concentration in a plasma display panel with a SrCaO cold cathode

We present here measurements of high Xe-contents plasma display panel (PDP) with SrCaO cold cathode. Luminous efficacy (η) shows a two-step increase with Xe-concentration in Ne/Xe gas mixture: η drastically increases up to Xe-concentration of 30% (Xe: 30%), and then attains 5 lm/W at the highest Xe-concentration of Xe: 100%. The high performance PDP with Xe: 100% can be operated at low applied voltage between 230 and 377 V due to the high secondary electron emission from the SrCaO cathode. Emission measurements clearly show the change in discharge characteristics at Xe: 30%, where the discharge changes from a Ne/Xe mixture discharge to an almost pure Xe discharge, and the vacuum ultraviolet (VUV) radiation from the combination of resonance and excimer radiations to only excimer radiation. Theoretical analysis solving Boltzmann equation for electron demonstrates that increasing Xe-concentration enhances the collision frequency for electron impact excitation directly from ground state to lower levels concerned with the VUV radiation, resulting in a drastic increase in luminous efficacy up to Xe: 30%. Also, one-dimensional fluid simulation of a Ne/Xe dielectric barrier discharge clearly shows that a combination of high secondary electron emission cathode and high Xe-concentration is quite effective for high VUV radiation efficiency because it induces a drastic increase in electron-heating efficiency.

Analysis on DC Glow Discharge Properties of Ar Gas at the Atmosphere Pressure

Atmosphere Plasma of Gas Discharge (APGD) has been used in plasma sources for material processing such as etching, deposition, surface modification and so on due to having no thermal damages. The APGD researches on AC source with high frequency have been mainly processed. However, DC APGD studies have been not. In order to understand APGD further, it is necessary to study on fundamental properties of DC APGD. In this paper, we developed a one-dimensional fluid simulation model with capacitively coupled plasma chamber at the atmosphere pressure (760 [Torr]). Nine kinds of Ar discharge particles such as electron (e), positive ions (, ) and neutral particles (, , , (1), (3) and Ar gas) are considered in the computation. The simulation was worked at the current range of 1~15 [mA]. The characteristics of voltage-current were calculated and the structure of Joule heating were discussed. The spatial distributions of Ar DC APGD and the mechanism of power consumption were also investigated.

Numerical Study on Characteristics of Argon Radio-Frequency Glow Discharge with Varying gas Pressure

A one-dimensional fluid simulation on argon rf glow discharge with varying linearly gas pressure from 1 Torr to 100Torr is performed. The model based on mass conservation equations for electron and ion under diffusion and mobility approximation, and the electron energy conservation equation is solved numerically by finite volume method. The numerical results show that a uniform plasma with high density can be obtained from rf glow discharge with varying gas pressure, and the density of plasma becomes higher as the gas pressure varies from 1 Torr to 100 Torr. It is also shown that in the range of the gas pressure from 1 Torr to 100 Torr with the slower rate of varying gas pressure, higher density of plasma can be obtained.