An objective definition of a vortex
2005; Cambridge University Press; Volume: 525; Linguagem: Inglês
10.1017/s0022112004002526
ISSN1469-7645
Autores Tópico(s)Vibration and Dynamic Analysis
ResumoThe most widely used definitions of a vortex are not objective: they identify different structures as vortices in frames that rotate relative to each other. Yet a frame-independent vortex definition is essential for rotating flows and for flows with interacting vortices. Here we define a vortex as a set of fluid trajectories along which the strain acceleration tensor is indefinite over directions of zero strain. Physically, this objective criterion identifies vortices as material tubes in which material elements do not align with directions suggested by the strain eigenvectors. We show using examples how this vortex criterion outperforms earlier frame-dependent criteria. As a side result, we also obtain an objective criterion for hyperbolic Lagrangian structures.
Referência(s)