TITLE:
Three-Dimensional Visualization of Shock Cell Structure and Screech Tone Emission in Underexpanded Circular Jet
AUTHORS:
Keita Ozawa, Takayuki Yamagata, Nobuyuki Fujisawa
KEYWORDS:
Screech Tone, Aeroacoustics, Directivity, Frequency Spectrum, Underexpanded Circular Jet, Schlieren Imaging
JOURNAL NAME:
Journal of Flow Control, Measurement & Visualization,
Vol.10 No.1,
December
7,
2021
ABSTRACT: The three-dimensional visualization of flow and screech-tone emission from an underexpanded circular jet is first investigated experimentally using high-speed cross-schlieren imaging and microphone measurements in the cross-sectional planes along the jet axis. This experimental technique allows the visualization of the shock-cell structure, directivity of sound intensity, and frequency spectrum in the cross-sectional planes of the screeching jet. The high-speed cross-schlieren observation of the screeching jet shows the occurrence of an asymmetrical shock-cell structure that is generated by the flapping mode in the screeching jet. This contributes to the generation of a screech tone propagating upstream along the jet axis and non-uniform sound intensities around the jet in circumferential direction. These observations by high-speed cross-schlieren imaging were validated by the microphone measurements.