Title: Energy flux enhancement, intermittency and turbulence via Fourier triad phase dynamics in 1D Burgers equation
Speakers: Dr. Miguel Bustamante (UCD)
Date: Monday 17th September 2018
Location: Room 1.25, Science Centre North
We present a theoretical and numerical study of Fourier space triad phase dynamics in one-dimensional stochastically forced Burgers equation at Reynolds number Re ≈ 2.7×10^4. We demonstrate that Fourier triad phases over the inertial range display a collective behaviour characterised by intermittent periods of synchronisation and alignment, reminiscent of Kuramoto model (Kuramoto 1984) and directly related to collisions of shocks in physical space. These periods of synchronisation favour efficient energy fluxes across the inertial range towards small scales, resulting in strong bursts of dissipation and enhanced coherence of Fourier energy spectrum. The fast time scale of the onset of synchronisation relegates energy dynamics to a passive role: this is further examined using a reduced system with the Fourier amplitudes fixed in time -- a phase-only model. We show that intermittent triad phase dynamics persists without amplitude evolution and we broadly recover many of the characteristics of the full Burgers system. In addition, for both full Burgers and phase-only systems the physical space velocity statistics reveals that triad phase alignment is directly related to the non-Gaussian statistics typically associated with structure-function intermittency in turbulent systems.
This work was done in collaboration with Dr. Brendan P. Murray. It is published in Journal of Fluid Mechanics 850, 624-645 (2018). You can find an arXiv preprint here: https://arxiv.org/abs/1705.08960.