The structure and dynamics of vorticity w, rate-of-strain S, and the full velocity gradient tensor A are studied using direct numerical simulations (DNS) of incompressible homogeneous turbulence. Results effectively characterize distinct dynamical behavior and provide a physical description of small-scale motion. The evolution of high amplitude events, defined according to the invariants of the local velocity gradient tensor, is observed through conditional Lagrangian statistics. In order to effectively describe the coupled interaction of w and S, the dynamics are examined in the basis of the principal strain eigenvectors. In this reference frame, the dynamic significance of the nonlocal effects through pressure are evident and the interaction through vortex stretching and through rotation of the principal axes of S are distinguished; the latter associated with the condition of misaligned w with respect to S which predominates in isotropic turbulence. Properties of the Burgers vortex, which illustrate implications of spatial structure, are considered and compared with those observed in homogeneous turbulence.

References:

Nomura, K.K. and Post, G.K., 1997 "The Structure and Dynamics of Vorticity and Rate-of-strain in Incompressible Homogeneous Turbulence," J. Fluid Mech. (submitted).

Nomura, K.K., Post, G.K., and Diamessis, P., 1997 "Characterization of Small-scale Motion in Incompressible Homogeneous Turbulence," 28th AIAA Fluid Dynamics Conference (Snowmass, Colorado), AIAA Paper 97-1956.