电弧射流激励器工作特性仿真研究

为了在高超声速飞行器减阻中达到更好的减阻效果,设计了一种电弧射流等离子体激励器。采用有限元法求解非线性多物理方程,对此电弧射流等离子体激励器的工作特性进行了数值模拟,得到了激励器内部的电势、压力、温度和速度分布,综合分析了进气口气体速度、放电电流、激励器管道半径对电势、压力、温度和速度分布的影响。获得了全面的影响规律,通过仿真结果还得到:电弧射流等离子体激励器可产生最高温度为8638 K、最高速度为655 m/s的等离子体射流。当电流20 A,进气速度0.5 m/s,管道半径2.5 mm时,所需功率最小;当电流20 A,入口气体流速5 m/s,管道半径2.5 mm时,出口处平均温度最高;当电流20 A,进口气体速度10 m/s,管道半径2.5 mm时,出口处平均速度最大。并对仿真得到的放电电压进行了实验验证,在等离子体参数相似的情况下,实验结果与仿真结果吻合较好。     

亚大气压六相交流电弧放电等离子体射流特性数值模拟

以临近空间高超声速飞行器和航天器再入大气环境飞行过程中其表面产生的高密度非平衡态等离子体为研究对象,基于本研究组所建立的多相交流电弧放电等离子体实验平台(MPX-2015),开展了非平衡态氩等离子体射流特性的二维数值模拟研究.在亚音速条件下二维、非平衡数值模拟所得到的计算结果与实验测量结果符合良好.超音速条件下的数值模拟结果表明,随着真空腔压强的降低,等离子体射流流速明显增大,覆盖钝体头部的等离子体鞘套的厚度先减小,而后又增加,鞘套的空间均匀性以及等离子体向钝体表面的总传热量均显著降低,而钝体头部的局部电子数密度则增大.数值模拟结果为在MPX-2015上开展超音速条件下的实验研究提供了理论指导.     

Numerical analysis of hybrid plasma generated by Nd:YAG laser and gas tungsten arc

When the output from a high power Nd:YAG laser irradiates a metallic surface, metal vapor is generated and changes into the plasma state, which is called a laser-induced plasma plume. If the high power laser is combined with an arc plasma, they mutually attract and influence each other. In this study, several analytic steps are introduced to analyze the laser-arc hybrid welding plasma. A conduction equation is first solved to obtain the temperature distribution on the metallic surface. Next, an analysis of the metal vapor is conducted to investigate the Ar–Fe mixture using a numerical method. As a result of the analysis, it is revealed that the plasma is concentrated in the vicinity of the laser-irradiation position and that the local temperature of the plasma is increased. Plasma flow and current density profiles are also affected by the laser irradiation.     

滑动弧低温等离子体放电特性的数值模拟研究

滑动弧等离子体的电弧温度场、电场和导电区域尺寸是确定电子温度、电子密度、化学反应速率以及能量效率的重要参数.对气流量为1.43 L/min和6.42 L/min时50 Hz交流滑动弧放电的电参数进行了测量;用瞬态的电弧模型描述滑动弧的能量传递,并用近似的介质电导率和热扩散系数对模型进行简化,解决了由于电弧结构变化所导致的移动边界问题;模拟求得等离子体的电弧结构、电场强度和动态温度场等参数的演化.其中,电弧电场的模拟值与实验值基本符合,计算得到电弧轴心温度可以达到5700—6700 K.研究结果表明,气流直 关键词： 滑动弧等离子体 温度场 电场强度 导电半径     

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为了提高等离子体废物处理效率,根据磁流体动力学理论,利用计算流体力学软件FLUENT,采用磁矢量势的方法对直流双阳极非转移型电弧等离子体炬进行了二维轴对称数值模拟。计算中采用了SIMPLE算法。数值模拟得到了等离子体的温度、速度等分布。结果表明,等离子体的温度随着轴向距离的增加而减小,随弧电流增加而增加;其速度随着轴向距离的增加而先增大后减小,随弧电流增加而增加;等离子体炬出口处的温度和速度随着径向距离的增加而减小。这些结果与实验结果基本相符。     

Imaging and spectrum diagnostics of air arc plasma characteristics

This paper is devoted to the study of the air arc plasma characteristics and consists of two parts. An optical high-speed imaging system is integrated with pressure sensing, arc current, and voltage measurement to investigate high-speed and high-temperature unsteady arc plasma motion in a molded case circuit breaker (MCCB) model, especially with the influence of polyoxymethylene (POM), polycarbonate (PBT), nylon, and ceramic arc chamber wall materials. It demonstrates that the performance can be improved effectively by adopting POM and nylon gassing materials. Also, spectrum diagnostics is introduced to analyze the influence of polymethylmethacrylate (PMMA) gassing material on the temperature of arc in a simple model. It shows that material added adjacent to cathode is more effective to cool the arc, compared with the case of anode.     

混合离子束阴极真空弧等离子体鞘层特性

基于无碰撞模型,建立了混合离子束阴极真空弧等离子体鞘层动力学模型,给出了解析表达式。针对材料改性中应用的H-Ti混合离子束,模拟计算了鞘层厚度和靶表面电场强度分别随离子密度和偏置靶压的演变规律。针对实际应用中出现的鞘层击穿和离子束散焦现象进行了理论分析,发现离子束稳定工作区域强烈依赖于离子密度和偏置靶压等参数,降低离子密度和提高靶压会增加稳定工作区域范围。     

混合离子束阴极真空弧等离子体鞘层特性

基于无碰撞模型,建立了混合离子束阴极真空弧等离子体鞘层动力学模型,给出了解析表达式。针对材料改性中应用的H-Ti混合离子束,模拟计算了鞘层厚度和靶表面电场强度分别随离子密度和偏置靶压的演变规律。针对实际应用中出现的鞘层击穿和离子束散焦现象进行了理论分析,发现离子束稳定工作区域强烈依赖于离子密度和偏置靶压等参数,降低离子密度和提高靶压会增加稳定工作区域范围。     

Improvement of laser keyhole formation with the assistance of arc plasma in the hybrid welding process of magnesium alloy

In the previous work, low-power laser/arc hybrid welding technique is used to weld magnesium alloy and high-quality weld joints are obtained. In order to make clear the interactions between low-power laser pulse and arc plasma, the effect of arc plasma on laser pulse is studied in this article. The result shows that the penetration of low-power laser welding with the assistance of TIG arc is more than two times deeper than that of laser welding alone and laser welding transforms from thermal-conduction mode to keyhole mode. The plasma behaviors and spectra during the welding process are studied, and the transition mechanism of laser-welding mode is analyzed in detail. It is also found that with the assistance of arc plasma, the threshold value of average power density to form keyhole welding for YAG laser is only 3.3×10⁴ W/cm², and the average peak power density is 2.6×10⁵ W/cm² in the present experiment. Moreover, the distribution of energy density during laser pulse is modulated to improve the formation and stability of laser keyholes.     

液相放电等离子体特性与激波特性的数值分析

以能量平衡方程为基础,采用不同的电导率唯象模型描述了液相放电等离子体圆柱形通道特性,得到了通道内半径、温度、电阻、电流和耗散能量随时间的变化关系,还给出了距离放电间隙中心一定距离处的冲击波压力变化,并与前人利用等离子体通道球状模型计算得到的结果进行了比较。结果表明：把等离子体通道看成球状和看成圆柱状在描述通道压力和通道半径时差异显著,而在描述其他物理特性时差别不大;三种电导率模型在描述等离子体通道物理特性时,变化趋势大体相同,而在描述激波特性时,电导率模型σ₂更符合实际;通过对比电学参数与压力参数的变化,就可以在实验中根据实验数据以及具体的研究问题进行模型的适用性选择。     

岩石物理模型约束下声波测井数据评价及处理*

声波测井数据是石油天然气勘探开发中最为重要的基础资料,其数据质量受井壁环境、频散等因素影响较大,且部分钻井并未采集声波。这对后续开展速度分析、储层识别和烃类检测都带来较大影响。因此需要对声波测井数据进行环境校正、补齐、预测等处理。目前,主要依据研究区域内已钻井的统计规律对声波测井数据进行评估和预测。而在深水区,因钻井距离远、地质条件差异较大等原因,不同地区的声波变化较大,依据统计方法评估数据存在较大的多解性。本文提出采用岩石物理模型来评估声波质量和预测声波数据。基于Xu&White岩石物理模型,采用密度曲线反演计算泥岩孔隙度,改善了岩石物理模拟在储层段和非储层段的拟合效果,且在多口井的适用性更好。基于新方法,本文建立了可在区域内稳定适用的岩石物理模型,可计算多口井在不同岩性、不同深度下的速度,为在不同地区和不同深度的声波质量评估和预测提供依据,指导后期储层预测和含气性检测。     

微束等离子体弧焊电弧物理特性多场耦合分析

根据磁流体动力学方程组,建立了微束等离子电弧模型,使用有限元分析软件COMSOL进行模拟计算。结果表明,电弧中心温度分布从钨针至焊件整体呈"毛笔"状,其中,喷嘴下方电弧形态呈"钟罩"形,在焊件上温度分布符合高斯分布特征;电弧等离子体在喷嘴内部速度较大,离开喷嘴后,其方向由喷嘴内的竖直向下逐渐变为到达工件时的向四周扩散;电流由焊件表面流出,经过弧柱区域流入钨针下端面,在钨针下端面附近取得最大值;电弧磁通密度分布呈"肺叶"状。最后进行了相应的熔焊试验,试验过程中拍摄的电弧轮廓与仿真电弧形态基本一致。     

Volt-ampere characteristics of a nitrogen DC plasma arc with anode melting

The characteristics of a nitrogen arc using a graphite cathode and a melting anode in a pilot-scale plasma furnace are investigated. The voltage is examined as a function of current and apparent plasma length. The voltage increases non-linearly with the increase of apparent plasma length, with the current fixed. The experimental data so obtained are compared with the predictions of the Bowman model for the electric arc, and with numerical simulations as well. The level of agreement between the experimental data at the melting anode and the numerical predictions confirms the suitability of the proposed the Bowman model. These characteristics are relevant to the engineering design and evaluation of a DC plasma furnace and reactor for the treatment of hazardous fly ash waste.     

含氘电极真空弧等离子体空间分布特性诊断研究

真空弧放电等离子体含有多种离子成分,并且各离子在空间上具有不同的分布规律.本文针对金属氘化物电极真空弧离子源,搭建了一台紧凑型磁分析装置,用来研究放电等离子体中氘离子与金属离子的空间分布.当离子源弧流为100 A左右时,该装置能有效地传输引出束流,并且具有较好的二次电子抑制效果,可准确获得各离子流强.利用该装置测量并获得了氘化钛含氘电极真空弧放电等离子体内氘离子和钛离子空间分布规律,结果表明:径向上,氘离子和钛离子都呈高斯分布,但氘离子分布均匀,而钛离子相对集中在轴线附近,导致轴线附近氘离子比例最低;轴向上,所有离子数量都以自然指数函数减少,而且相对幅度接近,所以氘离子比例几乎不变.本文研究结果不仅有助于理解真空弧放电等离子体膨胀过程,还可以指导金属氘化物电极真空弧离子源及其引出设计.     

Fluctuation of arc plasma in arc plasma torch with multiple cathodes

Fluctuation phenomena commonly exist in arc plasmas, limiting the application of this technology.In this paper,we report an investigation of fluctuations of arc plasmas in an arc plasma torch with multiple cathodes.Time-resolved images of the plasma column and anode arc roots are captured.Variations of the arc voltage, plasma column diameter, and pressure are also revealed.The results indicate that two well-separated fluctuations exist in the arc plasma torch.One is the high-frequency fluctuation(of several thousand Hz), which arises from transferring of the anode arc root.The other is the low-frequency fluctuation(of several hundred Hz), which may come from the pressure variation in the arc plasma torch.Initial analysis reveals that as the gas flow rate changes, the low-frequency fluctuation shows a similar variation trend with the Helmholtz oscillation.This oscillation leads to the shrinking and expanding of the plasma column.As a result, the arc voltage shows a sinusoidal fluctuation.     

保护气对切割弧特性影响的模拟研究

通过比较两种不同结构切割炬所产生的等离子体流场,发现保护气对等离子体的温度和速度分布影响很小.垂直保护气在切割炬喷口形成阻碍作用,造成切割炬内的压强有所升高,但是增加不大.两种结构保护气对切割弧的影响只是在炬喷口外的激波附近.加入保护气后激波的强度会减弱.相对于没有保护气的情况,保护气增加冷却作用,弧电压会略有升高.当改变保护气的成分时,发现弧柱区的氧气含量不受影响,所以保护气成分的改变不会影响到弧电压.计算发现轴线处氧气和周围气体的混合很少,在喷口下游10mm处,氧气的摩尔分数仍在90%以上. 关键词： 等离子体切割弧 保护气 数值模拟     

Spectral characteristics of arc plasma during laser-arc double-sided welding for aluminum alloy

In laser-arc double-sided welding, the spectral characteristics of the arc plasma are calculated and analyzed by spectroscopic diagnosis. The results show that, compared with conventional tungsten inert gas(TIG) welding,the introduction of a laser changes the physical characteristics of the arc plasma regardless of whether laser plasma penetration takes place, and that the influence of the laser mainly affects the near-anode region of the arc. When the laser power is relatively low, the arc column tends to compress, and the arc spectral characteristics show no significant difference. When the arc root constricts, compared with pure TIG arc, the electron density increases by ～2.7 times and the electron temperature decreases by ～3000 K. When the arc column expands, the intensities of spectral lines of both the metal and Ar atoms are the strongest. But it is also observed that the electron density reduces, whereas there is no obvious decrease of electron temperature.     

25kW氩壁稳电弧离子体LTE性的光谱学实验研究

本文利用光谱学诊断方法对25kW氩壁稳电弧等离子体的LTE性进行了实验研究.结果发现在实验条件下等离子体至少是PLTE的,压力高于0.05MPa、电流大于50A时,基本上是LTE的,谱线半宽度与等离子状态无关,只取决于电子密度.     

Analysis of plasma characteristics and conductive mechanism of laser assisted pulsed arc welding

This study aims to investigate the arc plasma shape and the spectral characteristics during the laser assisted pulsed arc welding process. The arc plasma shape was synchronously observed using a high speed camera, and the emission spectrum of plasma was obtained by spectrometer. The well-known Boltzmann plot method and Stark broadening were used to calculate the electron temperature and density respectively. The conductive mechanism of arc ignition in laser assisted arc hybrid welding was investigated, and it was found that the plasma current moved to the arc anode under the action of electric field. Thus, a significant parabolic channel was formed between the keyhole and the wire tip. This channel became the main method of energy transformation between the arc and the molten pool. The calculation results of plasma resistivity show that the laser plasma has low resistivity as the starting point of conductive channel formation. When the laser pulse duration increases, the intensity of the plasma radiation spectrum and the plasma electron density will increase, and the electron temperature will decrease.