Abstract
Experiments are performed in choked circular hot and cold nitrogen jets issuing from a 2.44 cm diameter sharp-edged orifice at a fully expanded jet Mach number of 1.85 in an effort to investigate the character of screech phenomenon. The stagnation temperature of the cold and the hot jets are 299 K and 319 K respectively. The axial distribution of the centerline Mach number was obtained with a pitot tube, while the screech data (frequency and amplitude) at different axial and radial stations were measured with the aid of microphones. The fundamental screech frequency of the hot jet is slightly increased relative to that of the cold jet. It is concluded that temperature effects on the screech amplitude are manifested with regard to the fundamental and the subharmonic even at relatively small temperature range considered.
Highlights
Supersonic jet screech represents an important concern as the intensity in the nearfield with a significant upstream directivity can induce fatigue and cause structural damage to aircraft and launch vehicles [1]-[3]
The center-line Mach number displays the characteristic oscillations of the underexpanded jet on account of the presence of the shock cell structures
The results suggest the existence of subharmonic screech in both the cold and the hot jets with a frequency of about 1.6 kHz
Summary
Supersonic jet screech represents an important concern as the intensity (as high as 170 to 180 dB) in the nearfield with a significant upstream directivity can induce fatigue and cause structural damage to aircraft and launch vehicles [1]-[3]. The fundamental physics of screech was uncovered by Powell [4] [5], who identified the mechanism of supersonic jet screech in terms of a resonant feedback loop. Several others followed it up with more details. It is generally believed that the screech tones are generated by the interaction between instability waves (vortices) developed from the nozzle lip area and the shock-cell structures [2]. It was recently shown [7] that screech
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