Ultrasound as a probe of turbulence

Lund, Fernando; Rojas, Cristián Guerra

doi:10.1016/0167-2789(89)90155-3

Cited by 90 publications

(99 citation statements)

References 24 publications

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“…The second term in this expression is the one obtained by Pitaevskii (1959), Ferziger (1974, Fabrikant (1983) and Lund & Rojas (1989), and has the standard form for diffraction in two dimensions. It vanishes when θ = ±π/2, which accounts for the lack of oscillations at θ = ±π/2 in the scattering cross-sections shown in figures 3 and 4.…”

Section: Far-field Analysismentioning

confidence: 99%

“…As previously mentioned, Lund & Rojas (1989) have proposed using ultrasound to probe turbulence in laboratory experiments. In a typical experimental setting, the sensors, which detect the scattered sound field, will be placed several acoustic wavelengths from the vortex.…”

Section: Far-field Analysismentioning

confidence: 99%

“…Examples are the propagation of sound through turbulence (Kraichnan 1953;Lighthill 1953;Batchelor 1956), and the propagation of sound through the wakes of jet engines (Ferziger 1974). Lund & Rojas (1989) have proposed using ultrasound to probe turbulence in laboratory experiments (see also Labbé & Pinton 1998;Oljaca et al 1998).…”

Section: Introductionmentioning

confidence: 99%

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Scattering of acoustic waves by a vortex

Ford

Smith

1999

J. Fluid Mech.

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We investigate the scattering of a plane acoustic wave by an axisymmetric vortex in two dimensions. We consider vortices with localized vorticity, arbitrary circulation and small Mach number. The wavelength of the acoustic waves is assumed to be much longer than the scale of the vortex. This enables us to define two asymptotic regions: an inner, vortical region, and an outer, wave region. The solution is then developed in the two regions using matched asymptotic expansions, with the Mach number as the expansion parameter. The leading-order scattered wave field consists of two components. One component arises from the interaction in the vortical region, and takes the form of a dipolar wave. The other component arises from the interaction in the wave region. For an incident wave with wavenumber k propagating in the positive X-direction, a steepest descents analysis shows that, in the far-field limit, the leadingorder scattered field takes the form i(π − θ)e ikX + 1 2 cos θ cot ( 1 2 θ)(2π/kR) 1/2 e i(kR−π/4) , where θ is the usual polar angle. This expression is not valid in a parabolic region centred on the positive X-axis, where kRθ 2 = O(1). A different asymptotic solution is appropriate in this region. The two solutions match onto each other to give a leading-order scattering amplitude that is finite and single-valued everywhere, and that vanishes along the X-axis. The next term in the expansion in Mach number has a non-zero far-field response along the X-axis.

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Section: Far-field Analysismentioning

confidence: 99%

Section: Far-field Analysismentioning

confidence: 99%

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Scattering of acoustic waves by a vortex

Ford

Smith

1999

J. Fluid Mech.

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“…More recently, Lund and Rojas [21] have derived a convenient expression that connects the acoustic scattered pressure, scat p directly to the Fourier transform of the vorticity field:…”

Section: Sound-vorticity Interactionmentioning

confidence: 99%

An ultrasonic contactless sensor for breathing monitoring

Arlotto

Grimaldi

Naeck³

et al. 2015

Sleep Medicine

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Abstract:The monitoring of human breathing activity during a long period has multiple fundamental applications in medicine. In breathing sleep disorders such as apnea, the diagnosis is based on events during which the person stops breathing for several periods during sleep. In polysomnography, the standard for sleep disordered breathing analysis, chest movement and airflow are used to monitor the respiratory activity. However, this method has serious drawbacks. Indeed, as the subject should sleep overnight in a laboratory and because of sensors being in direct contact with him, artifacts modifying sleep quality are often observed. This work investigates an analysis of the viability of an ultrasonic device to quantify the breathing activity, without contact and without any perception by the subject. Based on a low power ultrasonic active source and transducer, the device measures the frequency shift produced by the velocity difference between the exhaled air flow and the ambient environment, i.e., the Doppler effect. After acquisition and digitization, a specific signal processing is applied to separate the effects of breath from those due to subject movements from the Doppler signal. The distance between the source and the sensor, about 50 cm, and the use of ultrasound frequency well above audible frequencies, 40 kHz, allow monitoring the breathing activity without any perception by the subject, and therefore without any modification of the sleep quality which is very important for sleep disorders diagnostic applications. This work is patented (patent pending 2013-7-31 number FR.13/57569).

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“…1. Ultrasonic vorticity probe is based on scattering of ultrasonic waves by the flow vorticity at a chosen wave vector [3,1]. In order to insure the noninvasiveness of the probe, it was necessary to add a thin wall between the transducers (transmiter and receiver) and the flow.…”

Section: Experimental Facility and Sensorsmentioning

confidence: 99%