Regensburg 2022 – wissenschaftliches Programm

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DY: Fachverband Dynamik und Statistische Physik

DY 34: Fluid Physics: Turbulence and Convection

DY 34.5: Vortrag

Mittwoch, 7. September 2022, 16:45–17:00, H19

Towards an effective description of turbulent superstructures in simple shear flows — •Fabián Álvarez-Garrido and Michael Wilczek — Theoretical Physics I, University of Bayreuth, Bayreuth

Turbulent flows driven by large-scale forces such as convection, shear, or rotation may display large-scale coherent flows, namely turbulent superstructures, coexisting with fully developed turbulence on the small scales. A complete description of these flows involves innumerable degrees of freedom, yet turbulent superstructures seem to evolve according to a comparably lower-dimensional set of equations. In addition, despite the ubiquity of turbulent superstructures, their interplay with the smaller scales is not yet fully understood. We study a simple shear-driven flow, the three-dimensional Kolmogorov flow. The large scales in this flow feature the formation of large-scale vortex pairs. Moreover, the system exhibits permanent dynamics between states having a different number of vortex pairs. Employing amplitude equations, we characterize the dynamics of the large scales close to the onset of the vortex pairs. We show that the dynamics close to the onset correspond to the one of a two-dimensional flow. Furthermore, we show that far from the onset, the derived model captures the structure of the large-scale vortices. Based on data from direct numerical simulations, we introduce new stochastic terms to these amplitude equations to model the contribution of the small scales to the dynamics of the large ones. These modified amplitude equations can qualitatively reproduce the dynamics of these large-scale vortex pairs and shed light on the role of small-scale turbulence in the formation of turbulent superstructures.