Dispersion of swimming algae in laminar and turbulent channel flows: consequences for photobioreactors

Abstract

Shear flow significantly affects the transport of swimming algae in suspension. For example, viscous and gravitational torques bias bottom-heavy cells to swim towards regions of downwelling fluid (gyrotaxis). It is necessary to understand how such biases affect algal dispersion in natural and industrial flows, especially in view of growing interest in algal photobioreactors. Motivated by this, we here study the dispersion of gyrotactic algae in laminar and turbulent channel flows using direct numerical simulation (DNS) and the analytical swimming dispersion theory of Bees and Croze (2010). Time-resolved dispersion measures are evaluated as functions of the Peclet and Reynolds numbers in upwelling and downwelling flows. For laminar flows, DNS results are compared with theory using competing descriptions of biased swimming cells in shear flow. Excellent agreement is found for predictions that employ generalized-Taylor-dispersion. The results highlight peculiarities of gyrotactic swimmer dispersion relative to passive tracers. In laminar downwelling flow the cell distribution drifts in excess of the mean flow, increasing in magnitude with Peclet number. The cell effective axial diffusivity increases and decreases with Peclet number (for tracers it merely increases). In turbulent flows, gyrotactic effects are weaker, but discernable and manifested as non-zero drift. These results should significantly impact photobioreactor design.

31 pages, 15 figures (includes supplementary materials)

References in corpus (3)

• Biased swimming cells do not disperse in pipes as tracers: a population model based on microscale behaviour
• Dispersion of biased swimming microorganisms in a fluid flowing through a tube
• Sheared bioconvection in a horizontal tube

Cited by in corpus (16)

• Turbulent fluid acceleration generates clusters of gyrotactic microorganisms
• Accumulation of motile elongated micro-organisms in turbulence
• Gyrotactic swimmer dispersion in pipe flow: testing the theory
• Gyrotactic swimmers in turbulence: shape effects and role of the large-scale flow
• Transient dispersion process of active particles
• Gyrotactic phytoplankton in laminar and turbulent flows: a dynamical systems approach
• A local approximation model for macroscale transport of biased active Brownian particles in a flowing suspension
• Swimming strategy of settling elongated microswimmers by reinforcement learning
• Resonant alignment of microswimmer trajectories in oscillatory shear flows
• Bifurcation and stability of downflowing gyrotactic micro-organism suspensions in a vertical pipe
• A Lagrangian model of copepod dynamics: Clustering by escape jumps in turbulence
• Active Particle Diffusion in Convection Roll Arrays
• A sequence of transcritical bifurcations in a suspension of gyrotactic microswimmers in vertical pipe
• Taylor$\unicode{x2013}$Aris dispersion of active particles in oscillatory channel flow
• Fine-tuning the dispersion of active suspensions with oscillatory flows
• Orientation Dynamics of Gyrotactic Microswimmers in Turbulent Flows