Measuring Oscillatory Velocity Fields Due to Swimming Algae

TL;DR

This study presents the first time-resolved measurements of oscillatory velocity fields caused by swimming algae, revealing complex flow structures and quantifying the mechanical power and energy dissipation involved.

Contribution

It introduces a novel experimental approach to measure and analyze the oscillatory velocity fields generated by swimming unicellular microorganisms.

Findings

Velocity fields are complex and time-dependent.

Flow scales inversely with distance from the algae.

Mechanical power peaks at 15 femtowatts, with dissipation over four times higher than steady swimming.

Abstract

In this fluid dynamics video, we present the first time-resolved measurements of the oscillatory velocity field induced by swimming unicellular microorganisms. Confinement of the green alga C. reinhardtii in stabilized thin liquid films allows simultaneous tracking of cells and tracer particles. The measured velocity field reveals complex time-dependent flow structures, and scales inversely with distance. The instantaneous mechanical power generated by the cells is measured from the velocity fields and peaks at 15 fW. The dissipation per cycle is more than four times what steady swimming would require.