Roll Instability in Neutral Boundary Layers Induced by Free-stream Turbulence
Abstract
Adopting the perspective of statistical state dynamics (SSD) has led to a number of recent advances in understanding atmospheric turbulence at both boundary layer and planetary scale. Traditionally, realizations have been used to study turbulence and if a statistical quantity was needed it was obtained by averaging. However, a great advantage of the SSD approach is that it reveals directly the essential cooperative mechanisms of interaction among spatial and temporal scales that underly many phenomena in turbulence. A closure at second order is used in this work to analyze a novel instability emergent from the statistical interaction between coherent perturbations of roll form and incoherent turbulence in a boundary layer. By perturbing the nonlinear SSD dynamics a new manifold of stable modes with roll structure is shown to exist in the presence of small amplitude turbulence. With increase in a parameter controlling the turbulence energy, a member of this set of stable manifold is destabilized at a bifurcation and the associated roll eigenmode is found to equilibrate at finite amplitude. This bifurcation structure predicted by SSD is verified using fully nonlinear simulations.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFMNG24A..08F
- Keywords:
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- 3325 Monte Carlo technique;
- ATMOSPHERIC PROCESSESDE: 3265 Stochastic processes;
- MATHEMATICAL GEOPHYSICSDE: 3275 Uncertainty quantification;
- MATHEMATICAL GEOPHYSICSDE: 4468 Probability distributions;
- heavy and fat-tailed;
- NONLINEAR GEOPHYSICS