Nonlinear synchronization in open flows

The selection criteria governing finite-amplitude synchronized oscillating states are discussed for model systems and real wake flows in a domain of i nfinite streamwise extent. Two types of nonlinear global modes are possible : hat modes with overall smoothly varying amplitude and elephant modes with a sharp front. The vortex street in wake flows is of elephant type, as obs erved in direct numerical simulations of a real spatially developing wake. Furthermore, the elephant frequency selection criterion is in excellent agr eement with the numerically determined vortex shedding frequency. (C) 2001 Academic Press.