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Final PhD Seminar

Coherent bundle-wall coupling in two-dimensional turbulence

Mr Mahdi Davoodianidalik
Australian National University

Two-dimensional (2D) turbulence arises from the confinement of fluid turbulence to two spatial dimensions. Many aspects of 2D turbulence (e.g. inverse energy cascade and spectral condensation) are relevant for physical systems. Faraday wave-driven turbulence (FWDT) is one of the most recent experimental setups used to study 2D turbulence. Recent studies on FWDT resulted in the discovery of the coherent bundle structure underlying turbulence flows. Here we present the experimental findings of the flow-wall coupling between these coherent bundles and finite-size elements.

We uncover a fluctuation-induced force between two beams floating in 2D turbulence. Fluctuation-induced forces are observed in numerous physical systems spanning from quantum to macroscopic scale. However, there is as yet no experimental report of their existence in hydrodynamic turbulence. Here we present evidence of an attraction force mediated via turbulent fluctuations by using two walls locally confining 2D turbulence. This long-range interaction is a function of the wall separation and the energy injection rate in the turbulent flow. The force generation mechanism is rooted in a nontrivial fluid-wall coupling where the cavity walls guide coherent flow structures. This discovery provides a valuable experimental framework that can be used to study and understand force generation in the out-of-equilibrium systems.

Interaction between a rotating disk and 2D turbulence is investigated as a curved wall coupling with bundles. Our study shows that the rotational dynamics of the disk are strongly connected to the coherent structure of the flow. Rotational fluctuation of the disk is maximum when the diameter of the disk is close to the width of the bundles in the flow. Using these findings, we have successfully developed a method to shape bacterial cellulose into spheres with different diameters.

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