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DY: Fachverband Dynamik und Statistische Physik

DY 4: Fluid Physics and Turbulence

DY 4.4: Vortrag

Montag, 18. März 2024, 10:30–10:45, BH-N 128

Low-dimensional description of turbulent superstructures in three-dimensional Kolmogorov flow — •Fabián Álvarez-Garrido and Michael Wilczek — Theoretische Physik I, Universität Bayreuth, Bayreuth, Germany

Certain flows display the coexistence of small-scale turbulence and large-scale turbulent superstructures. Despite the ubiquity of these structures, their interplay with the smaller scales is not yet fully understood. We investigate the three-dimensional Kolmogorov flow as a model flow displaying turbulent superstructures, namely, it features large-scale quasi-two-dimensional vortex pairs. Moreover, we observe non-periodic transitions between states with one and two pairs of these large-scale vortices. We identify these different large-scale states as remnants of two solutions that emerge when a laminar solution looses stability at low Reynolds number where no turbulent fluctuations are present. This allows us to characterize the dynamics of the large scales by keeping track of two complex amplitudes. Through conducting direct numerical simulations, we gathered statistics on these two complex amplitudes and constructed a set of stochastic amplitude equations. The statistical properties of this low-dimensional system can reproduce, up to a fair agreement, the ones observed in the fully three-dimensional Kolmogorov flow. Based on these results, we discuss how the transfer of energy from the large to the smaller scales can stabilize the large-scale vortices, and how the fast-evolving fluctuations can enable the switching between large-scale states, mimicking the mechanism behind noise-induced transitions.

Keywords: Turbulence; Self-organization; Noise-induced transitions