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Multi-particle dispersion during entrainment in turbulent free-shear flows

Published online by Cambridge University Press:  16 September 2016

Tomoaki Watanabe ,
Carlos B. da Silva  and
Koji Nagata
Tomoaki Watanabe*
Affiliation:
Department of Aerospace Engineering, Nagoya University, Nagoya 464-8603, Japan
Carlos B. da Silva
Affiliation:
IDMEC, Instituto Superior Técnico, Universidade de Lisboa, Lisboa 1049-001, Portugal
Koji Nagata
Affiliation:
Department of Aerospace Engineering, Nagoya University, Nagoya 464-8603, Japan
*
†Email address for correspondence: [email protected]
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Abstract

Multi-particle dispersion is studied using direct numerical simulations of temporally evolving mixing layers and planar jets for tetrahedra consisting of four fluid particles which are seeded in the turbulent regions or in the non-turbulent regions near the turbulent/non-turbulent interface (TNTI). The modified Richardson law for decaying turbulence is observed for particle pairs. The size dependence of the mean and relative motions of the entrained tetrahedra indicates that the characteristic length scale of the entrained lumps of fluid is approximately 10 times the Kolmogorov microscale. When the tetrahedra move within the TNTI layer they are flattened and elongated by vortex stretching at a deformation rate that is characterized by the Kolmogorov time scale. The shape evolutions of the tetrahedra show that in free-shear flows, thin-slab structures of advected scalars are generated within the TNTI layers.

JFM classification

Wakes/Jets: Shear layers Turbulent Flows: Turbulent Flows Mixing: Turbulent mixing
Type
Rapids
Information
Journal of Fluid Mechanics , Volume 805 , 25 October 2016 , R1
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Copyright
© 2016 Cambridge University Press 

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