The alignment of vortical structures in turbulent flow through a contraction
Pugazenthi, R. S.
Speirs, Nathan Bevan
Thoroddsen, Sigurdur T
KAUST DepartmentDivision of Physical Science and Engineering, King Abdullah University of Science and Technology(KAUST), Thuwal 23955-6900, Saudi Arabia
Fluid and Plasma Simulation Group (FPS)
High-Speed Fluids Imaging Laboratory
Mechanical Engineering Program
Physical Science and Engineering (PSE) Division
Online Publication Date2019-12-03
Print Publication Date2020-02-10
Permanent link to this recordhttp://hdl.handle.net/10754/660519
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AbstractWe 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-thebox 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 centre line 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.
CitationMugundhan, V., Pugazenthi, R. S., Speirs, N. B., Samtaney, R., & Thoroddsen, S. T. (2019). The alignment of vortical structures in turbulent flow through a contraction. Journal of Fluid Mechanics, 884. doi:10.1017/jfm.2019.887
SponsorsThis study was supported by King Abdullah University of Science and Technology (KAUST) under grant URF/1/2981-01-01. We thank S. Taguchi and Y. Otsu for their help in running some of the early experiments. We acknowledge the help of R. Carolan for designing the active grids and M. Abdulkareem for programming them.
PublisherCambridge University Press (CUP)
JournalJournal of Fluid Mechanics
Except where otherwise noted, this item's license is described as This is an Open Access article, distributed under the terms of the Creative CommonsAttribution-NonCommercial-NoDerivatives licence (http://creativecommons.org/licenses/by-nc-nd/4.0/), which permits non-commercial re-use, distribution, and reproduction in any medium, provided the original work is unaltered and is properly cited. The written permission of Cambridge University Press must be obtained for commercial re-use or in order to create a derivative work. doi:10.1017/jfm.2019.887