Random focusing of nonlinear acoustic <i>N</i>-waves in fully developed turbulence: Laboratory scale experiment

Averiyanov, Mikhail; Ollivier, Sébastien; Khokhlova, Vera A.; Blanc‐Benon, Philippe

doi:10.1121/1.3652869

Cited by 29 publications

(44 citation statements)

References 44 publications

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“…This definition of the rise time, which corresponds to the steepest region of the front, was recently proposed from laboratory-scale sonic boom studies to characterize shock structures of sparkgenerated pulses propagating in air. 46,47 The definition is equivalent to the classical definition (time needed for the pressure at the shock of the amplitude A s to increase from 0.1ÁA s to 0.9ÁA s ) for shocks governed by the stationary solution of the Burgers equation: 48…”

Section: B Measurement Protocols and Pulse Definitionsmentioning

confidence: 99%

Acoustic field characterization of the Duolith: Measurements and modeling of a clinical shock wave therapy device

Perez

Chen

Matula

et al. 2013

The Journal of the Acoustical Society of America

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Extracorporeal shock wave therapy (ESWT) uses acoustic pulses to treat certain musculoskeletal disorders. In this paper the acoustic field of a clinical portable ESWT device (Duolith SD1) was characterized. Field mapping was performed in water for two different standoffs of the electromagnetic head (15 or 30 mm) using a fiber optic probe hydrophone. Peak positive pressures at the focus ranged from 2 to 45 MPa, while peak negative pressures ranged from -2 to -11 MPa. Pulse rise times ranged from 8 to 500 ns; shock formation did not occur for any machine settings. The maximum standard deviation in peak pressure at the focus was 1.2%, indicating that the Duolith SD1 generates stable pulses. The results compare qualitatively, but not quantitatively with manufacturer specifications. Simulations were carried out for the short standoff by matching a Khokhlov-Zabolotskaya-Kuznetzov equation to the measured field at a plane near the source, and then propagating the wave outward. The results of modeling agree well with experimental data. The model was used to analyze the spatial structure of the peak pressures. Predictions from the model suggest that a true shock wave could be obtained in water if the initial pressure output of the device were doubled.

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Section: B Measurement Protocols and Pulse Definitionsmentioning

confidence: 99%

Acoustic field characterization of the Duolith: Measurements and modeling of a clinical shock wave therapy device

Perez

Chen

Matula

et al. 2013

The Journal of the Acoustical Society of America

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“…1). 6 The repetition rate of the pulses was 1 Hz; the wavefront was assumed to have a spherical geometry. Acoustic pulses introduced variations of air density and, as a result, variations of the optical refractive index which are schematically shown in Fig.…”

Section: A Experimental Arrangement For Optical Measurementsmentioning

confidence: 99%

Characterization of spark-generated N-waves in air using an optical schlieren method

Karzova

Yuldashev

Khokhlova

et al. 2015

The Journal of the Acoustical Society of America

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Accurate measurement of high-amplitude, broadband shock pulses in air is an important part of laboratory-scale experiments in atmospheric acoustics. Although various methods have been developed, specific drawbacks still exist and need to be addressed. Here, a schlieren optical method was used to reconstruct the pressure signatures of nonlinear spherically diverging short acoustic pulses generated using an electric spark source (2.5 kPa, 33 μs at 10 cm from the source) in homogeneous air. A high-speed camera was used to capture light rays deflected by refractive index inhomogeneities, caused by the acoustic wave. Pressure waveforms were reconstructed from the light intensity patterns in the recorded images using an Abel-type inversion method. Absolute pressure levels were determined by analyzing at different propagation distances the duration of the compression phase of pulses, which changed due to nonlinear propagation effects. Numerical modeling base on the generalized Burgers equation was used to evaluate the smearing of the waveform caused by finite exposure time of the high-speed camera and corresponding limitations in resolution of the schlieren technique. The proposed method allows the study of the evolution of spark-generated shock waves in air starting from the very short distances from the spark, 30 mm, up to 600 mm.

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“…In the laboratory-scale experiments which simulate the N-shaped waveform, a front and tail shock waves have the same waveform deformed by turbulent effects [10,30]. It seems that the front and tail shock waves receive the same shock focusing/diffracting effects.…”

Section: Turbulence Interaction With Long Rise-time Signaturementioning

confidence: 99%

“…Salze et al [29] showed a shock propagation distance relates to a transverse shock focusing region and experimentally estimated its shock focal region. Averiyanov et al [28,30] showed that an overpressure decrease and the arrival time are governed by the large scale of a velocity fluctuation, and the small scales of a velocity fluctuation mainly cause increasing the rise time. In the typical model experiments [10,29,30], in order to simulate the N-shaped sonic boom propagation in the real atmosphere, the characteristic length scales, such as a wavelength, a turbulent interaction distance, and the geometrical turbulence length scales, were adjusted.…”

Section: Introductionmentioning

confidence: 99%

Turbulent jet interaction with a long rise-time pressure signature

2016

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Abstract:A sonic boom signature with a long rise time has the ability to reduce the sonic boom, but it does not necessarily minimize the sonic boom at the ground level because of the real atmospheric turbulence. In this study, an effect of the turbulence on a long rise-time pressure signature was experimentally investigated in a ballistic range facility. To compare the effects of the turbulence on the long and short rise-time pressure signatures, a cone-cylinder projectile that simultaneously produces these pressure signatures was designed. The pressure waves interacted with a turbulent field generated by a circular nozzle. The turbulence effects were evaluated using flow diagnostic techniques: high-speed schlieren photography, a point-diffraction interferometer, and a pressure measurement. In spite of the fact that the long and short rise-time pressure signatures simultaneously travel through the turbulent field, the turbulence effects do not give the same contribution to these overpressures. Regarding the long risetime pressure signature, the overpressure fluctuation due to the turbulence interaction is almost uniform, and a standard deviation 1.5 times greater than that of the no-turbulence case is observed. By contrast, a short rise-time pressure signature which passed through the same turbulent field is strongly affected by the turbulence. A standard deviation increases by a factor of 14 because of the turbulence interaction. Additionally, there is a non-correlation between the overpressure fluctuations of the long and short rise-time pressure signatures. These results deduce that the length of the rise time is important to the turbulence effects such as the shock focusing/diffracting.

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Random focusing of nonlinear acoustic N-waves in fully developed turbulence: Laboratory scale experiment

Cited by 29 publications

References 44 publications

Acoustic field characterization of the Duolith: Measurements and modeling of a clinical shock wave therapy device

Acoustic field characterization of the Duolith: Measurements and modeling of a clinical shock wave therapy device

Characterization of spark-generated N-waves in air using an optical schlieren method

Turbulent jet interaction with a long rise-time pressure signature

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