Journal article
Alec J Petersen, Lucia Baker, Filippo Coletti
Journal of Fluid Mechanics, vol. 864, 2019, pp. 925-970
Journal of Fluid Mechanics, vol. 864, 2019, pp. 925-970
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APA
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Petersen, A. J., Baker, L., & Coletti, F. (2019). Experimental study of inertial particles clustering and settling in homogeneous turbulence. Journal of Fluid Mechanics, 864, 925–970.
Chicago/Turabian
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Petersen, Alec J, Lucia Baker, and Filippo Coletti. “Experimental Study of Inertial Particles Clustering and Settling in Homogeneous Turbulence.” Journal of Fluid Mechanics 864 (2019): 925–970.
MLA
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Petersen, Alec J., et al. “Experimental Study of Inertial Particles Clustering and Settling in Homogeneous Turbulence.” Journal of Fluid Mechanics, vol. 864, 2019, pp. 925–70.
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@article{alec2019a,
title = {Experimental study of inertial particles clustering and settling in homogeneous turbulence},
year = {2019},
journal = {Journal of Fluid Mechanics},
pages = {925-970},
volume = {864},
author = {Petersen, Alec J and Baker, Lucia and Coletti, Filippo}
}
Abstract
Background: The dynamics of particles carried by turbulent fluid flows is rich with complex and coupled phenomena,
Objectives:
Methods: Utilizing a zero-mean-flow air turbulence chamber, we drop size-selected solid particles and study their dynamics with particle imaging and tracking velocimetry at multiple resolutions. The carrier flow is simultaneously measured by particle image velocimetry of suspended tracers, allowing the characterization of the interplay between both the dispersed and continuous phases.
Results: Clustering is confirmed to be most intense for Stη ≈ 1, but it extends over larger scales for heavier particles. Individual clusters form a hierarchy of self-similar, fractal-like objects, preferentially aligned with gravity and with sizes that can reach the integral scale of the turbulence. Remarkably, the settling velocity of Stη ≈ 1 particles can be several times larger than the still-air terminal velocity, and the clusters can fall even faster. This is caused by downward fluid fluctuations preferentially sweeping the particles, and we propose that this mechanism is influenced by both large and small scales of the turbulence. The particle–fluid slip velocities show large variance, and both the instantaneous particle Reynolds number and drag coefficient can greatly differ from their nominal values. Finally, for sufficient loadings, the particles generally augment the small-scale fluid velocity fluctuations, which however may account for a limited fraction of the turbulent kinetic energy.
Conclusions: The present experimental approach has allowed us to gain insight into several outstanding issues in particle-laden turbulence. The jet-stirred homogeneous air turbulence chamber is particularly suitable to characterize the considered regime: the lack of mean flow enables the unbiased measurement of the settling velocity, also yielding a much larger dynamic range for the velocity fluctuations compared to wind tunnel experiments (Carter and Coletti 2017). Moreover, the large region of homogeneous turbulence is crucial for the particles to interact with the full range of turbulent scales (Bellani and Variano 2014). The simultaneous imaging of both phases allows the characterization of their interplay, within the inherent limits posed by the imaging accuracy and its planar nature. Finally, the relatively high Reλ provides the separation of scales needed to identify the dominant flow parameters.
Objectives:
Methods: Utilizing a zero-mean-flow air turbulence chamber, we drop size-selected solid particles and study their dynamics with particle imaging and tracking velocimetry at multiple resolutions. The carrier flow is simultaneously measured by particle image velocimetry of suspended tracers, allowing the characterization of the interplay between both the dispersed and continuous phases.
Results: Clustering is confirmed to be most intense for Stη ≈ 1, but it extends over larger scales for heavier particles. Individual clusters form a hierarchy of self-similar, fractal-like objects, preferentially aligned with gravity and with sizes that can reach the integral scale of the turbulence. Remarkably, the settling velocity of Stη ≈ 1 particles can be several times larger than the still-air terminal velocity, and the clusters can fall even faster. This is caused by downward fluid fluctuations preferentially sweeping the particles, and we propose that this mechanism is influenced by both large and small scales of the turbulence. The particle–fluid slip velocities show large variance, and both the instantaneous particle Reynolds number and drag coefficient can greatly differ from their nominal values. Finally, for sufficient loadings, the particles generally augment the small-scale fluid velocity fluctuations, which however may account for a limited fraction of the turbulent kinetic energy.
Conclusions: The present experimental approach has allowed us to gain insight into several outstanding issues in particle-laden turbulence. The jet-stirred homogeneous air turbulence chamber is particularly suitable to characterize the considered regime: the lack of mean flow enables the unbiased measurement of the settling velocity, also yielding a much larger dynamic range for the velocity fluctuations compared to wind tunnel experiments (Carter and Coletti 2017). Moreover, the large region of homogeneous turbulence is crucial for the particles to interact with the full range of turbulent scales (Bellani and Variano 2014). The simultaneous imaging of both phases allows the characterization of their interplay, within the inherent limits posed by the imaging accuracy and its planar nature. Finally, the relatively high Reλ provides the separation of scales needed to identify the dominant flow parameters.
© Cambridge University Press 2019. This is a work of the U.S. Government and is not subject to copyright protection in the United States.