高速等离子体射流在多个领域都发挥着不可或缺的作用。等离子体射流不同于常规的气体或液体的流动，其内部的电离状态、丰富的反应活性、多样的特征尺度、热平衡与非平衡共存等特点导致传统测速方法难以应用。为此本文开展了二维特征信号图像测速法（SSIV2D）的研究，特征信号图像测速法通过将羽流光强波动作为示踪信号来测量速度，从而拥有更好的流体跟随性和测量精度。

        本文首先将一维特征信号图像测速理论扩展至二维，用于测量射流速度分布。详细介绍了SSIV2D方法的计算流程，并讨论了在计算过程中参数选择的基本准则。随后介绍了低压直流电弧的实验系统，主要包括等离子体射流产生与特性测量系统。在放电过程中，实时记录射流电流电压波动曲线，采用光谱仪和高速相机捕获羽流发光强度的波动。

        二维特征信号图像测速方法在低压（约100 Pa）超声速等离子体射流的实验环境中得到验证，通过追踪射流内禀波动与人工引入的扰动，成功测量了羽流的二维流场速度。结果显示，流线分布与膨胀区的特征相符，通过跟踪人工施加扰动得到的速度分布和大小与放电参数下的射流流动特性相吻合。为进一步证实SSIV2D方法的有效性，将其测量结果与静电探针组获得的速度数据进行了比较。两种方法得到的速度值呈现出良好的一致性，为SSIV2D方法作为二维测速技术的可行性验证提供了强有力的支持。此外，该比较分析还突显了SSIV2D方法在捕捉可压缩等离子体流场动态中的优势。SSIV2D方法的发展和验证丰富了等离子体流场测量的技术手段，为工业领域中等离子体流动控制与优化提供了一种新的工具。

        其次，本文基于特征信号图像测速技术，对不同工况下（电弧电流、气流量）以及多组分（氩-氦）等离子体的射流速度进行了测量，以进一步研究该技术在可压缩等离子体射流中的测量效果。通过使用696.5 nm窄带滤光片，进一步提取了混合气体等离子体射流中单一谱线所对应的射流速度。分析结果显示，在相同的工况（即相同的电功率、气体质量流量及背景气压）下，氩-氦混合等离子体射流的平均速度显著高于纯氩等离子体射流速度。此外，对于氩-氦混合等离子体射流，基于整体光强波动测得的射流速度明显超过了仅对应于Ar I特征谱线的组分传播速度。该结果表明，SSIV技术不仅能够测量流场的平均速度，还能够区分不同组分的速度场，展示了其在复杂流场测量中的高度适用性和优越性。

High-speed plasma jets play an indispensable role in several fields. Plasma jets are different from conventional gas or liquid flows, and their internal ionisation state, rich reactivity, diverse characteristic scales, and coexistence of thermal equilibrium and nonequilibrium make traditional velocimetry methods difficult to apply. In this paper, we carry out the study of two-dimensional specific signal image velocimetry (SSIV2D), which measures the velocity by using the plume light intensity fluctuation as a tracer signal, thus possessing better fluid-following and measurement accuracy.

In this paper, the theory of one-dimensional specific signal image velocimetry is first extended to two dimensions for measuring jet velocity distribution. The computational flow of the SSIV2D method is described in detail, and the basic guidelines for parameter selection in the computational process are discussed. Subsequently, the experimental system for low-voltage DC arcs is presented, which mainly includes a plasma jet generation and property measurement system. During the discharge process, the jet current-voltage fluctuation curves were recorded in real time, and the fluctuations of the plume luminescence intensity were captured using a spectrometer and a high-speed camera.

The two-dimensional specific signal image velocimetry method was validated in an experimental setting of a low-pressure (~ 100 Pa) supersonic plasma jet, and the two-dimensional flow field velocity of the plume was successfully measured by tracking the endowment fluctuations of the jet with artificially introduced perturbations. The results show that the streamline distribution is consistent with the characteristics of the expansion region, and the velocity distribution and magnitude obtained by tracking the artificially applied perturbations match the jet flow characteristics at the discharge parameters. To further confirm the validity of the SSIV2D method, its measurements were compared with the velocity data obtained from the electrostatic probe set. The velocity values obtained by the two methods show good agreement, providing strong support for the validation of the feasibility of the SSIV2D method as a 2D velocimetry technique. In addition, this comparative analysis highlights the advantages of the SSIV2D method in capturing the dynamics of compressible plasma flow fields. The development and validation of the SSIV2D method enriches the technical means of plasma flow field measurements, and provides a new tool for the control and optimisation of plasma flows in industry.

Secondly, in this paper, based on the specific signal image velocimetry technique, the jet velocities of different operating conditions (arc current, gas flow rate) as well as multi-component (argon-helium) plasma are measured in order to further investigate the measurement effect of this technique in compressible plasma jets. The jet velocity corresponding to a single spectral line in a mixed-gas plasma jet was further extracted by using a 696.5 nm narrowband filter. The analysis results show that the average velocity of the argon-helium mixed plasma jet is significantly higher than that of the pure argon plasma jet under the same working conditions (i.e., the same electric power, gas mass flow rate, and background air pressure). In addition, for the argon-helium hybrid plasma jet, the jet velocity measured based on the overall light intensity fluctuations significantly exceeds the component propagation velocities corresponding only to the Ar I eigen-spectral lines. This result shows that the SSIV technique is not only capable of measuring the average velocity of the flow field, but also of distinguishing the velocity fields of different components, demonstrating its high applicability and superiority in the measurement of complex flow fields.