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A Lagrangian study of inhomogeneous turbulence

Abstract : Inhomogeneous turbulence is experimentally investigated in a Lagrangian framework. Measurements of tracer and non-tracer particles in a turbulent channel were made, and were used to extract Lagrangian statistics conditioned on their initial distance to the channel wall. Highly resolved in time and space, these measurements provide the three components of position, velocity, and acceleration along a particle trajectory from very close to the channel wall (approx 10) to the channel center. Lagrangian time correlations allow the direct measurement of velocity and acceleration timescales in each direction, and characterize the inhomogeneity and anisotropy of the turbulent channel from the Lagrangian perspective. Small scale-anisotropy, characterized by the skewness and the correlation of the components of the acceleration, was found to be significant throughout the channel. Significant scale separation between the magnitude and components of acceleration was found across the channel, even in the near-wall region. Two classes of non-tracer particle trajectories were also measured, allowing direct comparison of tracer and non-tracer statistics from the highly-sheared anisotropic zone near the channel wall to the more homogeneous outer layer. Non-tracer acceleration statistics in the turbulent channel were found to be significantly different from similar results in homogeneous, isotropic turbulence. These statistics are necessary components of advanced Lagrangian stochastic models to predict dispersion and mixing in inhomogeneous turbulence.
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Nickolas Stelzenmuller. A Lagrangian study of inhomogeneous turbulence. Fluids mechanics [physics.class-ph]. Université Grenoble Alpes, 2017. English. ⟨NNT : 2017GREAI109⟩. ⟨tel-01739689⟩

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