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BP: Fachverband Biologische Physik
BP 7: Active Fluids and Microswimmers (joint session DY/BP/CPP)
BP 7.3: Talk
Monday, March 18, 2024, 15:45–16:00, BH-N 243
Active turbulent mixing — •Till Welker1, Malcolm Hillebrand2, Ricard Alert2, and Holger Stark1 — 1Institute of Theoretical Physics, TU Berlin, Germany — 2MPI for the Physics of Complex Systems, Dresden, Germany
Mixing on the mesoscale is crucial for both microfluidic devices and living cells. Experiments backed by simulations show a significant increase in mixing efficiency caused by active turbulence.
Our goal is to enhance the theoretical understanding of active turbulent mixing by transferring theories and concepts originally developed for inertial turbulent mixing. We therefore study a defect-free active nematic model known to show universal scaling of the energy spectrum with a passive chemical diffusing and advecting in the flow.
The efficiency of mixing χ rises with both activity of the nematic A and diffusion coefficient of the chemical D. Intriguingly, as D approaches zero, mixing efficiency converges to a non-zero value χ0(A) because smaller D are compensated by larger concentration gradients. This presents an attractive mechanism to mix poorly diffusive substances, and is also observed in inertial turbulent mixing.
The scaling of the concentration spectrum Ec(q) is of great interest and has been extensively studied in the context of inertial turbulence. We demonstrate that Batchelor-Howells-Townsend theory and Batchelor theory for strongly and poorly diffusive substances can be transferred to active turbulence. As a consequence of the universal energy scaling of our active nematic, we predict universal scaling regimes for Ec(q) which we validate in simulations.
Keywords: Active Turbulence; Mixing; Scaling