Observation of acoustic emission from head-on collision of two vortex rings

Minota, T.; Kambe, Tsutomu

doi:10.1016/s0022-460x(86)81422-5

Cited by 21 publications

(23 citation statements)

References 3 publications

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“…Thus the research on vortex sound has a close relationship to research on jet noise. Vortex sound theory, originally developed by Powell [16], and refined by Möhring [17] and others, was first experimentally tested by Kambe et al [18][19][20]. The experimental work of Kambe et al shows that the theory does a reasonably good job of predicting the noise generated by the head-on collision of two vortex rings.…”

Section: Iia Vortex Soundmentioning

confidence: 99%

Time-Domain Analysis of Subsonic Jet Noise

Kearney-Fischer

Sinha

Samimy

2012

50th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition

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Following on previous works showing that jet noise has significant intermittent aspects, the present work assumes that these intermittent events are the dominant feature of jet noise. A definition and method of detection for intermittent noise events is devised and implemented. Using a large experimental database of acoustically subsonic jets with different acoustic Mach numbers (M a = 0.5 -0.9), diameters (D = 2.54, 5.08, & 7.62 cm), and exit temperature ratios (ETR = 0.84 -2.70), these events are extracted from the noise signals measured in the anechoic chamber of the NASA Glenn AeroAcoustic Propulsion Laboratory. It is shown that a signal containing only these events retains all of the important aspects of the acoustic spectrum for jet noise radiating to shallow angles relative to the jet downstream axis, validating the assumption that intermittent events are the essential feature of low angle jet noise. The characteristics of these noise events are analyzed showing that these events can be statistically described in terms of three parameters (the variance of the original signal, the mean width of the events, and the mean time between events) and two universal statistical distribution curves. The variation of these parameters with radiation direction, diameter, velocity, and temperature are discussed. A simple model for this kind of signal is formulated and used to derive a relationship between the characteristics of the noise events and the fluctuations in the integrated noise source volume.

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Section: Iia Vortex Soundmentioning

confidence: 99%

Time-Domain Analysis of Subsonic Jet Noise

Kearney-Fischer

Sinha

Samimy

2012

50th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition

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“…in the absence of external bodies (nor forces). Green's function in free space is given by (45) which is to be substituted in (43). It is assumed that the point of observation x is at large distances from the point y located within the vortex flow, i.e.…”

Section: Vortex Sound In Free Spacementioning

confidence: 99%

“…Thus, for an oblique collision of two vortex rings, the acoustic pressure at r = |x| (= x) in the far field is given by (56) [34], where p is used instead of p F , the functions Q i (t), Q ij (t) and Q ijk (t) are defined by (34) and (35), t r ≡ t -r/c (retarded time), and Observed amplitudes p m (t) and p q (t). [45] γ being the ratio of specific heats (γ = 7/5 of the air leads to (5 -3γ)/12 = 1/15). The superscript (n) denotes the n-th time derivative, e.g.…”

Section: General Problemmentioning

confidence: 99%

Vortex Sound with Special Reference to Vortex Rings: Theory, Computer Simulations, and Experiments

Kambe¹

2010

International Journal of Aeroacoustics

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This is a review paper on vortex sound with special reference to vortex rings and sound emission detected in experimental tests. Any unsteady vortex motion excites acoustic waves. From the fundamental conservation equations of mass, momentum and energy of fluid flows, one can derive a wave equation of aerodynamic sound. The wave equation of acoustic pressure can be reduced to a compact form, called the equation of vortex sound. This equation predicts sound generation by unsteady vortex motions. On the other hand, based on the matched asymptotic expansion (using the multipole expansions), one can derive a formula of wave pressure excited by time-dependent vorticity field localized in space. The theoretical predictions are compared with experimental observations and direct computer simulations. The systems considered are, head-on collision or oblique collision of two vortex rings, vortex-cylinder interaction, vortex-edge interaction, and others. Scaling laws of the pressure of emitted sound are predicted by the theory and compared with experimental observations. Comparison between theories and observations shows excellence of the theoretical predictions. Direct numerical simulations are reviewed briefly for sound generation by collisions of two vortex rings and that by a cylinder immersed in a uniform stream (aeolian tones). Vortex sound in superfluid is also reviewed about experimental observations and computational studies on the basis of the Gross-Pitaevski equation. 52 Vortex sound with special reference to vortex rings: theory, computer simulations, and experiments approach of vorticity-potential method by Ishii et al. (1998) [22] to solve numerically the three-dimensional viscous vorticity equation. Section 5 presents sound emission by vortex-body interaction. General mathematical formulation is first presented for the wave generated by vortex-body interaction. It is found that the acoustic wave profile can be related to a time derivative of volume flux (through the vortex ring) of an imaginary potential flow around the body (something like the Faraday's law in the electromagnetism), characterized as a dipolar emission. Experimental tests were carried out for some particular arrangements of vortex-body system such as a vortex motion interacting with a circular cylinder [46], or with a sphere [47]. Section 7 describes sound generation by a vortex interacting with a sharp edge [33]. The wave is characterized by cardioid profiles. All the wave emissions were detected experimentally. The experimental tests were successful in showing remarkable agreement between the theory and experiment, summarized in [27]. In the mathematical analyses of the vortex-body interaction, vortex shedding is disregarded. Consideration is restricted only to the interaction of a vortex ring with a solid body in the above cases. Even though that is the case, the agreement is remarkable in the cases of experimental tests described above. Oscillations of vortex core of a vortex ring emit sound waves [36]. A review article by Kopiev and Cher...

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“…[1][2][3][4] Acoustic sound generated by a collision of vortex rings is also a fundamental problem in vortex sound. A lot of studies have been done for head on as well as oblique collisions both experimentally [5][6][7][8] and computationally. [8][9][10][11][12] Vortex sound is the sound produced as a by-product of unsteady fluid motions, and is part of the more general subject of aerodynamic sound.…”

Section: Introductionmentioning

confidence: 99%

Sound generation by head-on and oblique collisions of two vortex rings

Nakashima¹

2008

Physics of Fluids

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Sound generation by head-on and oblique collisions of two vortex rings with equal strength is investigated by a direct numerical simulation. The three-dimensional, unsteady, compressible Navier-Stokes equations are solved by a finite difference method, not only for a near-vortical field but also for a far-acoustic field. The theory of vortex sound is also applied to investigate the detailed relation between the vortex ring motion and the acoustic wave mode. Generation of two sound pressure waves, which are called the first and second pulses, is observed in the numerical results. The theoretical results show that, for the head-on collision, the generations of the first and second pulses are due to the variations of vorticity moment, associated with a decrease in the translational velocity of the vortex ring near the collision plane and its stretching motion, respectively. On the other hand, for the oblique collision, in addition to such generation mechanisms, the reconnection of vortex lines also affects the generation of the second pulse. The reconnection of vortex lines occurs more rapidly for a smaller collision angle, and therefore its contribution to the second pulse becomes large. In fact, in the oblique collision at a right angle, the generation of the second pulse is closely related to the reconnection of vortex lines, which can be seen by analyzing both the near and far fields. Furthermore, for a smaller collision angle, the reconnection of vortex lines leads to more rapid variation of the vorticity, which enhances asymmetric features of the second pulse exhibited by the octupole mode ͑third-order wave mode͒.

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Observation of acoustic emission from head-on collision of two vortex rings

Cited by 21 publications

References 3 publications

Time-Domain Analysis of Subsonic Jet Noise

Time-Domain Analysis of Subsonic Jet Noise

Vortex Sound with Special Reference to Vortex Rings: Theory, Computer Simulations, and Experiments

Sound generation by head-on and oblique collisions of two vortex rings

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