This paper examines various methods for phase averaging the flowfield of a sweeping supersonic jet emanating from a scaled fluidic oscillator. Determination of the phase-averaged flowfield is challenging, especially at high oscillation frequencies where there is a jitter in the periodicity caused by its inherent fluid dynamics. Several phase-averaging approaches (including mathematical, signal processing, and phase-lock techniques) applied to time-resolved schlieren images of the flowfield are described. Criteria for evaluation are based on the image distribution per phase bin, the centerline intensity profile of the phase-averaged schlieren image, and the cross correlation of the images with the time-averaged reference image. Examination of the different methods based on the criteria shows that the zero-crossing method is sufficiently accurate and most suitable for the naturally oscillating flowfield investigated in this study. Although the phase-locked approach works well at specific phase angles, overall, it is found unsuitable for the current test conditions. The zero-crossing method applied to a sweeping supersonic jet schlieren reveals shock structure distortion when switching directions in the oscillation cycle. Results indicate that the zero-crossing method described in this study can also be extended to other non-time-resolved quantitative and qualitative flowfield measurement techniques using a simultaneously acquired time-resolved reference signal.

本文研究了对来自缩放流体振荡器的扫掠超音速射流的流场进行相位平均的各种方法。相位平均流场的确定具有挑战性，特别是在高振荡频率下，由于其固有的流体动力学导致周期性抖动。描述了应用于流场的时间分辨纹影图像的几种相位平均方法（包括数学、信号处理和锁相技术）。评估标准基于每个相位箱的图像分布、相位平均纹影图像的中心线强度分布以及图像与时间平均参考图像的互相关。根据标准对不同方法的检查表明，过零方法足够准确，最适合本研究中研究的自然振荡流场。虽然锁相方法在特定相位角下效果很好，但总的来说，它不适合当前的测试条件。应用于扫掠超音速射流纹影的过零方法揭示了在振荡周期中切换方向时的激波结构畸变。结果表明，本研究中描述的过零方法也可以扩展到使用同时获取的时间分辨参考信号的其他非时间分辨定量和定性流场测量技术。虽然锁相方法在特定相位角下效果很好，但总的来说，它不适合当前的测试条件。应用于扫掠超音速射流纹影的过零方法揭示了在振荡周期中切换方向时的激波结构畸变。结果表明，本研究中描述的过零方法也可以扩展到使用同时获取的时间分辨参考信号的其他非时间分辨定量和定性流场测量技术。虽然锁相方法在特定相位角下效果很好，但总的来说，它不适合当前的测试条件。应用于扫掠超音速射流纹影的过零方法揭示了在振荡周期中切换方向时的激波结构畸变。结果表明，本研究中描述的过零方法也可以扩展到使用同时获取的时间分辨参考信号的其他非时间分辨定量和定性流场测量技术。