Transition to Turbulence via Spatio-Temporal Intermittency,
ADVISORY GROUP FOR AEROSPACE RESEARCH AND DEVELOPMENT NEUILLY-SUR-SEINE (FRAN CE)
Pagination or Media Count:
This lecture presented a scenario of transition to turbulence specific to large aspect ratio systems. Starting with simulations on a model chosen for its relevance to the field of convective instabilities we characterized the spatio-temporal intermittent phase. Then we examined the transition process having recourse to simpler systems coupled maps lattices. This process appeared to involve the propagation of an information, laminarturbulent which seemed stochastic though it was generated by a deterministic dynamics. Concepts first introduced in the statistical physics of critical phenomena applied to directed percolation allowed us to account for most features of spatio-temporal intermittency, and especially the change of behavior at what turned out to be a true threshold. The implications of this approach are important because, in large aspect ratio systems, we have to face the possibility that what we think is turbulence may be simply a finite life-time but very long turbulent transient. If the percolation analogy is valid, then a threshold exists above which the turbulent state percolates through the system and turbulence has virtually no chance to decay.
- Fluid Mechanics