Effects of shear-thinning rheology on near-wall turbulent structures
Journal article, 2021

Turbulent channel flow simulation of a shear-thinning fluid is considered - see Arosemena et al. (J. Fluid Mech., vol. 908, 2021, p. A43) - and compared with a Newtonian base case to reveal the effects of the shear-dependent rheology on the near-wall structures. Analyses of different flow statistics revealed that, for the shear-thinning fluid case, the streamwise vortices appear to grow in size, depart from the wall and present a lessening in their intensity. Information regarding variations in the quasi-longitudinal vortices is also obtained from three-dimensional structures identified through a normalized -criterion. With shear-thinning rheology, it is shown that the structures are comprised of wall-attached and -detached families which are taller than for a Newtonian fluid. Also, for a given height, the structures appear to be longer, with approximately the same width and overall larger volume for the shear-thinning fluid case; albeit their fractal dimension remains the same when compared to the Newtonian base case. Moreover, it is observed that the number density of vortical structures decreases with shear-thinning fluid behaviour. These observations, in conjunction with the known changes to the longitudinal velocity structures which appear to be less streaky, more spanwise separated and thickened with shear-thinning rheology, strongly suggest that the near-wall self-sustaining process has been disrupted. As we move slightly away from the wall and with shear-thinning behaviour, the local increase in viscosity seems to lead to less energetic vortices whereas the streaks are provided with an additional source of energy due to fluctuations in viscosity.

rheology

turbulent boundary layers

Author

Arturo A. Arosemena

Norwegian University of Science and Technology (NTNU)

Ronnie Andersson

Chalmers, Chemistry and Chemical Engineering, Chemical Technology, Chemical Process and Reaction Engineering

Helge I. Andersson

Norwegian University of Science and Technology (NTNU)

Jannike Solsvik

Norwegian University of Science and Technology (NTNU)

Journal of Fluid Mechanics

0022-1120 (ISSN) 1469-7645 (eISSN)

Vol. 925 A37

Subject Categories

Geophysical Engineering

Fluid Mechanics and Acoustics

Condensed Matter Physics

DOI

10.1017/jfm.2021.657

More information

Latest update

9/9/2021 9