Dynamical systems theory provides a wealth of mathematical tools and geometrical concepts for explaining complex real-world phenomena. We utilize these in the investigation of fundamental fluid flow phenomena in laboratory experiments. In the past, we have demonstrated that low-dimensional models can explain the behavior of highly complex flows of a liquid crystal. More recently, the latest concepts regarding Lagrangian Coherent Structures have provided insight into the structure of turbulent fluid flow, the nature of unsteady flow separation and helped uncover internal wave attractors.
Funding for our research on Flow Transport is provided by the MIT Ferry Fund, the ONR and the NSF.
This image reveals the divergence of a nominally two-dimensional, turbulent flow field, from which we have uncovered the underlying Lagrangian skeleton of turbulence.
News
Publications
- Anisotropic particles focusing effect in complex flows
Séverine Atis, Matthieu Leclair, Themistoklis P. Sapsis, and Thomas Peacock
Phys. Rev. Fluids, 7, 084503 (2022)
Finite-size effects can lead neutrally buoyant particles to exhibit different dynamics than tracer particles, and can alter their transport properties in fluid flows. Here we investigate the effect of the particle’s shape on their dispersion in two-dimensional complex flows. Combining numerical simulations with laboratory experiments, we show that particles with isotropic and anisotropic shapes exhibit different Lagrangian coherent structures, resulting in distinct dispersion phenomena within a given flow field. Experiments with rod-shaped particles show a focusing effect in the vicinity of vortex cores. We present a simple model that describes the dynamics of neutrally buoyant ellipsoidal particles in two-dimensional flow and show that particle aspect ratio and orientation-dependent forces can generate clustering phenomena in vortices.
- Experimental generation of axisymmetric internal wave super-harmonics
Boury, S., Odier, P. & Peacock, T.
Physical Review Fluids, 6, 064801 (2021)
In this paper, we present an experimental study of weakly nonlinear interaction of axisymmetric internal gravity waves in a resonant cavity, supported by theoretical considerations. Contrary to plane waves in Cartesian coordinates, for which self-interacting terms are null in a linear stratification, the nonlinear self-interaction of an internal wave mode in axisymmetric geometry is found to be efficient at producing super-harmonics, i.e., waves whose frequencies are integer multiples of the excitation frequency. Due to the range of frequencies tested in our experiments, the first harmonic frequency is below the cutoff imposed by the stratification so the lowest harmonic created can always propagate. The study shows that the super-harmonic wave field is a sum of standing waves satisfying both the dispersion relation for internal waves and the boundary conditions imposed by the cavity walls, while conserving the axisymmetry.