The structure of intense vorticity in isotropic turbulence

Abstract

The structure of the intense-vorticity regions is studied in numerically simulated homogeneous, isotropic, equilibrium turbulent flow fields at four different Reynolds numbers, in the range Re, = 35-170. In accordance with previous investigators this vorticity is found to be organized in coherent, cylindrical or ribbon-like, vortices ('worms'). A statistical study suggests that they are simply especially intense features of the background, O(o'), vorticity. Their radii scale with the Kolmogorov microscale and their lengths with the integral scale of the flow. An interesting observation is that the Reynolds number y/v, based on the circulation of the intense vortices, increases monotonically with ReA, raising the question of the stability of the structures in the limit of Re,-z co. Conversely, the average rate of stretching of these vortices increases only slowly with their peak vorticity, suggesting that self-stretching is not important in their evolution. One-and two-dimensional statistics of vorticity and strain are presented; they are non-Gaussian and the behaviour of their tails depends strongly on the Reynolds number. There is no evidence of convergence to a limiting distribution in this range of Re,, even though the energy spectra and the energy dissipation rate show good asymptotic properties in the higher-Reynolds-number cases. Evidence is presented to show that worms are natural features of the flow and that they do not depend on the particular forcing scheme.

Velocity and temperature derivatives in high-Reynolds-number turbulent flows in the atmospheric surface layer. Part 1. Facilities, methods and some general results

“…with the self-amplification of the field of vorticity/strain fluctuations. According to these estimates, the contributions to the enstrophy production, associated with the mean velocity gradient, Antonia & Chambers (1980);3-5, Sreenivasan & Antonia (1997): 3, plane jet, 4, wake, 5, atmospheric boundary layer; 6, Kerr (1985); 7, Gibson, Stegen & Williams (1970); 8, Jimenes et al (1993); 9, Kholmyansky et al (2001a); 10, present work. ω i ω k S ik , Ω k ω i s ik , i.e.…”

Turbulent boundary layers and channels at moderate Reynolds numbers

“…Since the typical maximum vorticity of the compact vortices is a few times co' (Jiménez et al 1993;Tanahashi et al 2004), they are essentially decoupled from the mean velocity profile, and are approximately isotropic. In fact, the intensities of the three vorticity components are roughly equal above y + « 50, and their spectra also approximately agree with each other above that level.…”

Evolution of vortex-surface fields in viscous Taylor–Green and Kida–Pelz flows

“…Although coherent bundles of vortex lines with strong vorticity and tube-like geometry have been observed (e.g. She, Jackson & Orszag 1990;Jimenez et al 1993) and analysed (see Constantin, Procaccia & Segel 1995) in turbulence, the existence of globally smooth vortex surfaces in general three-dimensional flows remains an open problem. Within the Clebsch representation (see Lamb 1932;Truesdell 1954), defined a vortex-surface field (VSF) as a smooth scalar field whose iso-surfaces † Email address for correspondence: yy@caltech.edu…”