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The alignment of vortical structures in turbulent flow through a contraction

Publication Type : Journal Article

Publisher : Journal of Fluid Mechanics

Source : Journal of Fluid Mechanics, Volume 884 (2020)

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Campus : Coimbatore

School : School of Engineering

Department : Mechanical Engineering

Year : 2020

Abstract : We investigate experimentally the turbulent flow through a two-dimensional contraction. Using a water tunnel with an active grid we generate turbulence at Taylor microscale Reynolds number Reλ∼250 which is advected through a 2.5 : 1 contraction. Volumetric and time-resolved tomographic particle image velocimetry and shake-the-box velocity measurements are used to characterize the evolution of coherent vortical structures at three streamwise locations upstream of and within the contraction. We confirm the conceptual picture of coherent large-scale vortices being stretched and aligned with the mean rate of strain. This alignment of the vortices with the tunnel centreline is stronger compared to the alignment of vorticity with the large-scale strain observed in numerical simulations of homogeneous turbulence. We judge this by the peak probability magnitudes of these alignments. This result is robust and independent of the grid-rotation protocols. On the other hand, while the pointwise vorticity vector also, to a lesser extent, aligns with the mean strain, it principally remains aligned with the intermediate eigenvector of the local instantaneous strain-rate tensor, as is known in other turbulent flows. These results persist when the distance from the grid to the entrance of the contraction is doubled, showing that modest transverse inhomogeneities do not significantly affect these vortical-orientation results.

Cite this Research Publication : Vivek Mugundhan, Pugazenthi, R. S., Speirs, N. B., Samtaney, R., and Thoroddsen, S. T., “The alignment of vortical structures in turbulent flow through a contraction”, Journal of Fluid Mechanics, vol. 884, 2020.

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