Pressure field around a rectangular supersonic jet in screech

Abstract

Supersonic jet screech generated by a rectangular nozzle with a pair of side walls added is studied both experimentally and numerically. A detailed observation of screech phenomena contributes to an understanding of the mechanism of sound generation. The numerical simulation shows that computational aeroacoustics is effective for strongly coupled flow acoustic problems such as screech. Flow visualization by an acoustically triggered pulse laser schlieren system clearly shows the dynamic motion of the third shock cell in the flapping mode. A traveling shock is found to exist in the third shock cell, and the sound is generated at the moment when the traveling shock coalesces into the end shock of the third shock cell. The instantaneous pressure distribution on the side wall shows that a pressure wave convectively propagates along the shear layer in the near field of the jet, while it propagates acoustically in the vertical direction away from the jet. Numerical simulation shows similar aspects of screech to those obtained in the experiment: the screech frequency, the flowfield, the fluctuating pressure distribution, etc. The calculated acoustic intensity shows that the acoustic energy is radiated at the end of the compression portion of each shock cell. The source of the first shock cell seems to supply the acoustic energy to its own shear layer to sustain the oscillation. It is also shown that the dimple spots observed in the isoamplitude contours of the screech sound pressure are a result of the interaction between discrete sources located at the end of each shock cell.

The generation mechanism of higher screech tone harmonics in supersonic jets

“…Screech-cyclic events of new shock waves forming upstream of the original shock waves and subsequent merging have been observed (similarly to what was described by Suda, Manning & Kaji (1993) and Kaji & Nishijima (1996)). These so-called shock wave clapping events altered the appearance of the passing flow structures associated with screech.…”

Supersonic Jet Screech: Half-Century From Powell to the Present

“…Gutmark et al [80] noted that a rectangular jet at Mach numbers slightly above choking exhibited a symmetric mode and that this mode switched to an antisymmetric mode at a fully expanded Mach number of 1.15. Subsequently, Kaji and Nishijima [115], Suda et al [116], and Nishijima and Kaji [117] proved that rectangular jets are capable of sustaining both symmetric and asymmetric modes. Similar observations of symmetrical modes in edgetones and rectangular jet screech were made by Lin and Powell [114].…”

“…However, their unsteady shock motion studies were not pursued further for many years. Recently, Suda et al [116], Kaji and Nishijima [115], and Panda [103] resumed progress in understanding unsteady shock motions.…”

Shock-Refracted Acoustic Wave Model for Screech Amplitude in Supersonic Jets

“…Interestingly, the data reveal low-pressure dips (dimple spots) in the source strength. According to Kaji and Nishijima [10] these dips are believed to be generated by the interaction between sources. There is a possibility that they could also be due to the expansion regions in the flow.…”

“…Whereas screech frequency is controlled by the feedback acoustic waves, the screech intensity is governed primarily by the characteristics of the downstream propagating flow disturbances and their interaction with the shock-cell structures. Several detailed measurements [10,12,15,[19][20][21][22][23] and numerical viscous simulations [10,[24][25][26][27][28][29] have been reported and served to throw light on the subject. The experimental description of A-D mode switch (A1 , A2 , B, C, D) according to the jet operating parameters represents a notable step [12].…”