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.
Highlights
Since the finding of screech tone by Powell in 1953 [1], this topic of interest has been studied by many researchers, and the results are well summarized in some review papers [2]-[7], which covers a wide range of research from fundamental to applications
To confirm the formation of an axisymmetric flow field in the screeching circular jet at pressure ratio P0/Pa = 4, the total pressure distributions were measured by traversing the total pressure tube with 1 mm inner diameter along the x- and y-axes normal to the jet axis at several vertical positions z/d, where z is the vertical distance from the nozzle exit, and d is the nozzle exit diameter
The experimental technique allowed the visualization of shock-cell structure, directivity of sound, and frequency spectrum of the screeching jet through an analysis of sequential schlieren images captured by two high-speed cameras and microphone measurement
Summary
Since the finding of screech tone by Powell in 1953 [1], this topic of interest has been studied by many researchers, and the results are well summarized in some review papers [2]-[7], which covers a wide range of research from fundamental to applications. To understand the mechanism of the screech tone emission in the jet, schlieren imaging combined with the high-speed flow observation was utilized as a tool of flow visualization for studying the unsteady high-speed flow field, thereby enabling the understanding of the shockwave formation and acoustic sound field in the screeching jet [15]. This experimental technique allows the characterization of an acoustic wave generated in the screeching jet, and the screech tone is emitted toward the upstream, indicating the directivity of the sound in the plane along the jet axis upstream. This enables the first observation of the acoustic behavior of the screech tone in the circumferential plane normal to the jet axis of the underexpanded circular jet
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