Berlin 2018 – scientific programme

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DY: Fachverband Dynamik und Statistische Physik

DY 68: Poster: Complex Fluids, Glasses, Granular

DY 68.14: Poster

Thursday, March 15, 2018, 15:30–18:00, Poster A

Elastic turbulence at low Reynolds numbers and its control — •Reinier van Buel, Christian Schaaf, Leander Rolef, and Holger Stark — Institut für Theoretische Physik, Technische Universität Berlin, Hardenbergstr. 36, 10623 Berlin, Germany

Viscoelastic polymer solutions have remarkable qualities compared to their Newtonian counterparts. Especially at very small scales, such as employed in microfluidic devices, they enhance mixing and heat transfer. This is due to elastic turbulence [1], which bears the same qualities as inertial turbulence. The relevant dimensionless number for viscoelastic fluids is the Weissenberg number, which is the ratio of nonlinear stress to dissipation via linear stress relaxation. Plane Couette flows of viscoelastic fluids have been shown to exhibit an elastic subcritical instability at low Reynolds numbers whereas flows with curved stream lines are linearly unstable. The critical Weissenberg number is related to the curvature of the flow stream lines.

We report here on the onset of elastic turbulence in a two-dimensional Taylor-Couette geometry using numerical solutions of the Oldroyd B model as our constitutive equation. We observe a critical Weissenberg number that demarcates the transition from a stable to an elastic turbulent flow. We characterize the turbulent flow by observing a strong enhancement of flow resistance and a power-law decay of velocity power spectra, which show that the flow is activated on a broad range of temporal scales. Finally, we present first results on controlling the instability by using time-delayed feedback.

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