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Mesure lagrangienne en turbulence : mise en oeuvre et analyse

Abstract : The aim of this PhD thesis is to study experimentally turbulence from a lagrangian point of vue. We wish to track a particle of fluid during a time greater than the characteristic time of large scale motion. To achieve this requirement, we have produced a new measurement technique of the lagrangian velocity in a high Reynolds number turbulent flow. The method is based on the measurement of the Doppler shift of the sound scattered by a moving particle, when insonified by a continuous mono- chromatic ultrasonic. The scattered sound is received by an array of transducers and sent to fast and ultralow noise acquisition device build during this thesis. To extract the frequency of modulation due to the velocity, we developed a spectral analysis algorithm based on approximate maximum likelihood principle coupled with a Kalman filter. It gives access to the inertial and large time scales of the lagrangian velocity. The lagrangian velocity field is shown to be gaussian with an exponential auto- correlation. The lagrangian spectrum is then in agreement with a Kolmogorov scaling prediction in the inertial range. We also observe an intermittency that is stronger (in terms of structure exponents) than the eulerian one. It cannot be explained by the usual model based on dissipation. We propose that this intermittency is linked with the persistence of correlations of the absolute value of velocity increments over very long times.
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https://tel.archives-ouvertes.fr/tel-00003926
Contributor : Nicolas Mordant <>
Submitted on : Monday, December 8, 2003 - 5:52:36 PM
Last modification on : Friday, October 23, 2020 - 4:45:19 PM
Long-term archiving on: : Friday, April 2, 2010 - 7:15:57 PM

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  • HAL Id : tel-00003926, version 1

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Nicolas Mordant. Mesure lagrangienne en turbulence : mise en oeuvre et analyse. Acoustique [physics.class-ph]. Ecole normale supérieure de lyon - ENS LYON, 2001. Français. ⟨tel-00003926⟩

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