Letter to the Editor: An Experimental Study of Underexpanded Square Jet Noise

Experimental and Theoretical Investigations of Edge Tones in High Speed Jets

“…The vortex-shock interaction attributes to the generation of screechtone by a mechanism similar to the edge-tone generation. Brassard et al (23) and Jothi and Srinivasan (24) reported that the screech-tone frequency of the helical mode for a circular jet is approximately equal to that produced due to the square jet having the same hydraulic diameter. Figure 13 shows similar observations for the dominant edge-tone frequency for both circular and square jets.…”

“…The eigenfunction correspond to each eigenvalue is given by Eqs. (22) and (23). The entire set of eigenvalues can be characterized by azimuthal wavenumber, n and a radial wave number, m. The neutral wave mode which correspond to the nth azimuthal mode and the mth radial mode will be designated by (n, m) where n = 0 or 1 and m = 1, 2, 3, 4, ..…”

A Fast Time–domain Integration Method for Computing Non-Stationary Response Histories of Linear Oscillators With Discrete-Time Random Forcing

“…Derivative noise is generated here and elsewhere, by processing discrete white noise in the frequency domain via FFT, and is used merely to emulate the e!ect of using a low cut-o! frequency for non-white excitation such as in prematurely truncating a jet noise spectrum [7]. Figure 3(b) shows for discrete white noise excitation, a section of the transient response of the oscillator, driven by discrete white noise both with-and without "ltering.…”

“…Intrinsic damping levels in small space structures can be as low as 0)2% critical for low-frequency modes, but very much less than 0)1% for the higher modes of larger structures. Random forcing can occur on space structures as continuous or intermittent broadband noise (perhaps with screech tones) through turbulent #ow in ducting and pipes [6], from jet or thruster noise [7], from #ow inside high-speed machinery [8,9] and from the use of pyrotechnic devices [10]. Typically, this is characterized by a very high-frequency range, departure from normal or well-known distributions, and possible quiet periods, through intermittent activity on-board.…”

An Experimental Investigation on the Acoustic Excitation of a Thin Plate by Low-Speed Jets

“…There seems to be a need to address the di!erences among these studies. Furthermore, as pointed out by Verma and Rathakrishnan [11] and Brassard et al [12], the nozzle geometry has great in#uence on the jet noises.…”