W. G. Pritchard Lab Seminar: 4-5 PM, 116 McAllister Building

	          **Tuesday April 23, 2002**
	
Long-Range Interactions in High-Reynolds Number Homogeneous
  Turbulence and Consequences to Local Isotropy

James G. Brasseur

Department of Mechanical Engineering
Penn State University

Abstract:

Three related issues will be addressed in a discussion of scale
interactions in high Reynolds number turbulence, based on the Fourier
spectral decomposition of the Navier-Stokes equation for homogeneous
turbulence: (i) some fundamental issues of energy exchange within
triadic interactions, and general features of "local," "non-local," and
"distant" triadic interactions, (ii) a study in which the phase changes
at the small scales are found to be strongly influenced by distant
triadic interactions in stationary isotropically forced turbulence, and
(iii) the adjustment of the internal dynamics of interscale interactions
in a fully developed isotropic turbulence which has been anisotropically
forced from a state of decay to a nonequilibrium state of transient
change.  We argue that the spectrally long-range interactions move the
small viscous scales from isotropy when the large energy-containing
scales are anisotropic, that the anisotropy is of two general types in
spectral space (phase and energy), and that nonequilibrium turbulence is
particularly susceptible to the "anisotropising" influence of long-range
spectral dynamics.