The regular and chaotic dynamics of structures in fluid flows

“Order in chaos” is not an abstraction. It is a characteristic of real disordered processes and can be formulated quantitatively. In application to turbulence the term "order in chaos" means the existence of localized metastable states–structures. In this review experiments demonstrating that the nonlinear dynamics of these structures can be both regular and chaotic are discussed. Models on the basis of which it is possible to construct a theory of spatial-temporal chaos in an ensemble of structures and thereby to discuss turbulence with small and moderate values of the critical parameter (relative Reynolds number) are studied.