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Rapid path to transition via nonlinear localized optimal perturbations in a boundary-layer flow
S Cherubini1, P De Palma, J-Ch Robinet
1DIMeG and CEMeC, Politecnico di Bari, Bari, Italy. s.cherubini@gmail.com
Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics
|January 15, 2011
Summary
Nonlinear mechanisms can trigger boundary-layer flow transition to chaos. Optimized nonlinear perturbations, unlike linear ones, initiate this turbulent state, involving streamwise vortices and hairpin structures.
Area of Science:
- Fluid Dynamics
- Nonlinear Dynamics
- Turbulence
Background:
- Recent studies suggest purely nonlinear mechanisms can trigger transition in fluid flows.
- Understanding the transition from laminar to turbulent flow is crucial in fluid dynamics.
Purpose of the Study:
- To verify the hypothesis that localized nonlinear perturbations can induce a chaotic state in boundary-layer flow.
- To investigate the nonlinear route to turbulence.
Main Methods:
- Computed nonlinear optimal localized perturbations using energy optimization.
- Included nonlinear terms of the Navier-Stokes equations in the optimization process.
Main Results:
- Identified nonlinear optimal perturbations on the turbulent side of the laminar-turbulent boundary.
- Demonstrated that these perturbations lead to a chaotic state, unlike linear counterparts of equal initial energy.
- Observed the evolution of perturbations involving streamwise-inclined vortices and hairpin structures preceding breakdown.
Conclusions:
- Localized nonlinear perturbations are capable of triggering transition to a chaotic turbulent state in boundary-layer flows.
- The nonlinear route to turbulence involves specific vortical structures at different time scales.
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