Fine-tuning the dispersion of active suspensions with oscillatory flows

Area of Science:

• Fluid dynamics
• Biophysics
• Active matter physics

Background:

• Taylor dispersion describes solute transport influenced by flow and diffusion.
• Active suspensions, like gyrotactic swimmers, display complex dispersion due to self-propulsion and external torques.
• Optimizing dispersion is crucial for applications such as bioreactors, enhancing mixing and particle separation.

Purpose of the Study:

• Investigate the dispersion of active suspensions in a vertical channel under oscillatory pressure gradients (Womersley flow).
• Explore the influence of gyrotactic swimmers and their response to viscous torques on dispersion.
• Determine the effectiveness of oscillatory flows in controlling particle dynamics and enabling species separation.

Main Methods:

• Utilized Lagrangian simulations to model the behavior of active suspensions.
• Analyzed the impact of oscillatory flow parameters on drift and dispersion.
• Examined the limitations of traditional averaging techniques (Generalized Taylor Dispersion) for oscillatory flows.

Main Results:

• Oscillatory Womersley flows induce significant drift and enhance lateral and downstream dispersion.
• Periodic mixing between channel sides was observed, influenced by flow oscillations.
• Demonstrated the potential for species separation based on differing motile behaviors.
• Identified limitations of Generalized Taylor Dispersion when oscillatory timescales match cell dynamics.

Conclusions:

• Oscillatory flows offer a tunable mechanism to manipulate active suspension dispersion.
• Gyrotactic swimmers' behavior in Womersley flow deviates from predictions based on standard averaging methods.
• This research provides insights for designing advanced mixing and separation systems in microfluidics and bioreactors.