Self-amplification of the field of velocity derivatives in quasi-isotropic turbulence

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