Self-amplification of the field of velocity derivatives in quasi-isotropicturbulence

We report results of direct numerical simulations of the Navier-Stokes equa tions regarding the role of self-amplification of the field of velocity der ivatives, i.e., involving both vorticity and strain. The main result is tha t even at rather moderate values of the Reynolds number the self-amplificat ion totally dominates the process of production of the field of velocity de rivatives. The role of external forcing in this process is negligible. This dominance occurs not only in the mean, but practically pointwise throughou t the whole flow field. The property of self-amplification possesses a numb er of quantitative universal properties which are independent of the detail s of forcing. (C) 2000 American Institute of Physics. [S1070-6631(00)51112- X].