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Dec 1986

Volume 80, Issue S1, pp. S1-S128

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back to top Session CC. Physical Acoustics IV: Turbulence and Bubbles
Contributed Papers
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Sound amplitude fluctuations in the presence of atmospheric turbulence (A)

Henry E. Bass, Walt McBride, and John Noble

J. Acoust. Soc. Am. Volume 80, Issue S1, pp. S58-S58 (1986); (1 page)

Online Publication Date: 13 Aug 2005

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The fluctuations in received sound pressure levels at a microphone array 1 m above the ground and 5–100 m from a source 1–30 m off the ground have been recorded simultaneously with fluctuations in wind speed and temperature. The recordings were then played back through a multichannel analyzer which gives the number of acoustic cycles with peak amplitudes within 1024 amplitude intervals. Normalizing by the number of counts gives the probability of observing a given amplitude. These measurements were made at octave‐band preferred frequencies between 63 Hz and 8 kHz. At frequencies of 500 Hz and below, the probability distribution appears Gaussian. At higher frequencies, the distribution is better represented by a log normal distribution. In each case, the shape of the curve was dependent upon turbulence parameters (scale and magnitude). [Work supported by the Army Research Office.]
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The effect of varying scale on acoustic propagation over a smooth surface (A)

Michael T. Bobak and Richard Raspet

J. Acoust. Soc. Am. Volume 80, Issue S1, pp. S58-S59 (1986); (2 pages)

Online Publication Date: 13 Aug 2005

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In an earlier paper we reported on the incorporation of a measured spatially varying turbulence model into the turbulence effects theory of Clifford and Lataitis [J. Acoust. Soc. Am. Suppl. 1 79, S19 (1986)]. In the earlier paper the theory was evaluated only in the limits L0 ≫ (L/k)1/2 or L0 ≪ (L/k)1/2, where L0 is the turbulence scale, k the acoustic wavenumber, and L the propagation distance. The validity of the above conditions was compromised by the varying scale of the measured turbulence model. In this paper we report on the evaluation of the complete integrals of Clifford and Lataitis [J. Acoust. Soc. Am. 73, 1548–1550 (1983)] and discuss how these results vary from the approximate integrals.
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Experimental study of acoustic radiation from a boundary layer transition region (A)

J. C. Perraud and A. Julienne

J. Acoust. Soc. Am. Volume 80, Issue S1, pp. S59-S59 (1986); (1 page)

Online Publication Date: 13 Aug 2005

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Wall pressure fluctuations were measured on a rigid axisymmetric body in the CEPRA 19 low‐noise, anechoic wind tunnel, using flush‐mounted microphones placed from the laminar region to the fully turbulent boundary layer. Microphones placed in the laminar flow region are used to detect noise radiated from the transition region, which occurs naturally, without separation, under a slightly positive pressure gradient. Cross‐spectral analyses show upstream acoustic propagation in a very wide frequency band, 4–30 kHz, detected in the laminar region. A method of conditional analysis is then used to establish the sequence of events from the onset of near‐harmonic instability wave packets to the generation, about 10 ms later, of turbulent spots leading to the acoustic emission. This intermittent acoustic radiation is detected in the nearfield for wind velocities ranging from 20–70 ms. Farfield detection was not achieved probably because of instrument limitations and propagation effects. [Work supported by DRET, Direction des Recherches et Etudes Techniques.]
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The linear theory of the wall‐jet tone (A)

Dorothy Innes

J. Acoust. Soc. Am. Volume 80, Issue S1, pp. S59-S59 (1986); (1 page)

Online Publication Date: 13 Aug 2005

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The wall jet is one of a class of flows, of which the jet‐edge tone is typical, associated with the production of discrete frequency sound. We present an incompressible, inviscid model for the wall jet in which a uniform stream emerges from a two‐dimensional duct and flows along a flat wall of finite length L. A “phase‐locking” criterion leads to simple scaling laws for the tone frequency and stages of operation. Specifically, if f is the frequency of the tone generated in the nth stage, f  =  (U0/2b) (4b/L) (n + 83), the sound field assumes the familiar cardiodal shape associated with a dipole source located above a semi‐infinite wall. These predictions are in agreement with the experimental data of Horne et al. (AIAA Paper #81–2043). [Work supported by ONR.]
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Transient behavior of oscillating bubbles (A)

Andrea Prosperetti

J. Acoust. Soc. Am. Volume 80, Issue S1, pp. S59-S59 (1986); (1 page)

Online Publication Date: 13 Aug 2005

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Research on the behavior of bubbles in sound fields has mostly been concerned with the steady regime of oscillation. However, the use of the pulsed mode in ultrasonic devices for medical applications has rendered the transient behavior of practical interest as well. In this paper several aspects of the transient regime are investigated theoretically with particular consideration given to the thermal mechanisms affecting the internal pressure in the bubble. It is shown that these mechanisms introduce a “memory” effect in the bubble response. Analytical results are obtained for low forcing, and numerical ones when large‐amplitude effects are significant. Phase change effects and gas‐vapor mass diffusion in the case of hot liquids are also considered. [Work supported by ONR.]
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Scattering of light by a coated bubble in water near the critical and Brewster scattering angles (A)

Phillip L. Marston and Stuart C. Billette

J. Acoust. Soc. Am. Volume 80, Issue S1, pp. S59-S59 (1986); (1 page) | Cited 1 time

Online Publication Date: 13 Aug 2005

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Microbubbles in the ocean may be coated by a thin film of surfactant since such substances can be abundant in natural waters. Such films may affect the optical and acoustical properties of bubbles. We investigated theoretical light scattering patterns for a spherical gas bubble (of radius a) coated by a film of uniform thickness h and refractive index nf surrounded by water of refractive index n ω = 4/3. The patterns were computed from the partial‐wave series of Aden and Kerker for ka ranging from 100–2500, where 2π/k is the optical wavelength in water. The corresponding range of a is 7.5–189/μm; h ranged from 0–3/μm and nf was typically real and equal to 1.5. Noncoated bubbles exhibit coarse irradiance oscillations as the scattering angle θ decreases below a critical value for total reflection (θc = 82.8°); a broad minimum in the polarized irradiance is expected near the Brewster scattering angle θB = 106.3° [P. L. Marston et al., Appl. Sci. Res. 38, 373–383 (1982)]. Coatings shift the coarse oscillations towards larger θ when nf > nω in agreement with predictions of ray optics. If the irradiance near 82.8° is used to size bubbles, the effects of this shift are negligible for anticipated coating parameters. The minimum near θB, however, is predicted to be significantly lifted by coatings. [Work supported by NORDA and by ONR.]
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A model of laser‐induced bubble formation and collapse mechanism (A)

Joon‐Hyuk Kim, Sangbum Lee, Hyup Yang, and Ho‐Young Kwak

J. Acoust. Soc. Am. Volume 80, Issue S1, pp. S59-S59 (1986); (1 page)

Online Publication Date: 13 Aug 2005

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It is well known that the high power laser can produce the breakdown of liquid [M. P. Felix et al., Appl. Phys. Lett. 19, 484 (1971)]. The bubble formation and the shock wave emission after the breakdown have been observed simultaneously [W. Lauterborn and E. J. Ebeling, Appl. Phys. Lett. 31, 663 (1977)]. Usually, the cavity concept that the bubble is empty has been employed as an initial condition for the study of bubble motion. In this study, the initial conditions of the bubble evolution due to laser irradiation, i.e., the bubble wall velocity and the pressure inside the bubble just after the bubble evolution, were obtained from the bubble formation model proposed by Kwak and Panton [J. Phys. D 18, 647 (1985)]. Subsequent bubble evolution were calculated numerically by using the Gilmore equation in a compressible region and by using the Rayleigh equation in an incompressible region. The elapsing time from the bubble formation to the first bubble collapse and the farfield pressure signal at the first bubble collapse are in good agreement with the experimental results [W. Lauterborn (pp. 3–12) and V. S. Teslenko (pp. 30–34), both in Cavitation and Inhomogeneities in Underwater Acoustics, edited by W. Lauterborn (Springer, New York, 1980)]. Also, calculation results showed that shock strength and the amplitude of the pressure wave at the first collapse are strongly dependent upon the initial bubble wall velocity.
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