Regensburg 2022 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 36: Complex Fluids and Soft Matter 2 (joint session DY/CPP)

CPP 36.3: Talk

Thursday, September 8, 2022, 10:30–10:45, H18

Elastic Turbulence in von Kármán geometry — •Reinier van Buel and Holger Stark — Institut für Theoretische Physik, Technische Universität Berlin, Hardenbergstr. 36, 10623 Berlin, Germany

Elastic turbulence, occurring in viscoelastic fluid flow at vanishing Reynolds numbers, is an interesting flow state [1-4] and has been experimentally studied in the von Kármán geometry [1]. Elastic turbulence is especially appealing for the mixing of fluids on the micron scale, which is extremely challenging in Newtonian fluids where transport relies on diffusion. Here, we present a fully three-dimensional numerical investigation of the von Kármán flow using the Oldroy-B model [4]. We observe a non-axisymmetric mode with four-fold symmetry that drives the flow instability towards elastic turbulence and compare it to results obtained from a linear stability analysis. By analyzing the velocity fluctuations and defining an order parameter, we identify a bistable flow state above a sub-critical transition, which switches between a weakly chaotic flow state and elastic turbulence and exhibits hysteretic behavior. Furthermore, we reveal a sharp increase in the flow resistance at the transition to elastic turbulence, which we attribute to the elastic contribution of the work performed at the open side surface of the flow. Finally, an analysis of the spatial and temporal velocity power spectra confirms the turbulent nature of the flow.

[1] A. Groisman and V. Steinberg, Nature 405, 53 (2000).

[2] R. Buel, C. Schaaf, H. Stark, Europhys. Lett. 124, 14001 (2018).

[3] R. Buel and H. Stark, Sci. Rep. 10, 1-9 (2020).

[4] R. Buel and H. Stark, Phys. Fluids 34, 4 (2022).