Journal of Fluid Mechanics



Small-scale structure of the Taylor–Green vortex


Marc E.  Brachet a1p1, Daniel I.  Meiron a1, Steven A.  Orszag a1, B. G.  Nickel a2, Rudolf H.  Morf a3 and Uriel  Frisch a4
a1 Massachusetts Institute of Technology, Cambridge, MA 02139
a2 University of Guelph, Guelph, Ontario
a3 R.C.A. Laboratories, Zurich, Switzerland
a4 CNRS, Observatoire de Nice, 06-Nice, France

Article author query
brachet me   [Google Scholar] 
meiron di   [Google Scholar] 
orszag sa   [Google Scholar] 
nickel bg   [Google Scholar] 
morf rh   [Google Scholar] 
frisch u   [Google Scholar] 
 

Abstract

The dynamics of both the inviscid and viscous Taylor–Green (TG) three-dimensional vortex flows are investigated. This flow is perhaps the simplest system in which one can study the generation of small scales by three-dimensional vortex stretching and the resulting turbulence. The problem is studied by both direct spectral numerical solution of the Navier–Stokes equations (with up to 2563 modes) and by power-series analysis in time.

The inviscid dynamics are strongly influenced by symmetries which confine the flow to an impermeable box with stress-free boundaries. There is an early stage during which the flow is strongly anisotropic with well-organized (laminar) small-scale excitation in the form of vortex sheets located near the walls of this box. The flow is smooth but has complex-space singularities within a distance $\hat{\delta}(t)$ of real (physical) space which give rise to an exponential tail in the energy spectrum. It is found that $\hat{\delta}(t)$ decreases exponentially in time to the limit of our resolution. Indirect evidence is presented that more violent vortex stretching takes place at later times, possibly leading to a real singularity ($\hat{\delta}(t) = 0$) at a finite time. These direct integration results are consistent with new temporal power-series results that extend the Morf, Orszag & Frisch (1980) analysis from order t44 to order t80. Still, convincing evidence for or against the existence of a real singularity will require even more sophisticated analysis. The viscous dynamics (decay) have been studied for Reynolds numbers R (based on an integral scale) up to 3000 and beyond the time tmax at which the maximum energy dissipation is achieved. Early-time, high-R dynamics are essentially inviscid and laminar. The inviscidly formed vortex sheets are observed to roll up and are then subject to instabilities accompanied by reconnection processes which make the flow increasingly chaotic (turbulent) with extended high-vorticity patches appearing away from the impermeable walls. Near tmax the small scales of the flow are nearly isotropic provided that R [greater, similar] 1000. Various features characteristic of fully developed turbulence are observed near tmax when R = 3000 and Rλ = 110:

  1. a kn inertial range in the energy spectrum is obtained with n [approximate] 1.6–2.2 (in contrast with a much steeper spectrum at earlier times);
  2. th energy dissipation has considerable spatial intermittency; its spectrum has a k−1+μ inertial range with the codimension μ [approximate] 0.3−0.7.

Skewness and flatness results are also presented.

(Published Online April 20 2006)
(Received February 5 1982)
(Revised June 14 1982)


Correspondence:
p1 Present address: CNRS, Observatoire de Nice, 06-Nice, France.


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