Thrust and Hydrodynamic Efficiency of the Bundled Flagella

Area of Science:

• Biomimetic Micropropulsion
• Fluid Dynamics
• Robotics

Background:

• Prokaryotic flagellar motility inspires untethered microswimmers for medical applications.
• Measuring thrust and efficiency in multi-flagellar microswimmers is challenging due to complex fluid-structure interactions.

Purpose of the Study:

• To develop a methodology for measuring propulsive performance parameters of microswimmers.
• To compare different micropropulsion designs, particularly multi-flagellar configurations.

Main Methods:

• A novel methodology based on volumetric velocity field acquisition using digital particle image velocimetry (PIV) was developed.
• Experiments were conducted on scaled-up prototypes with computational fluid dynamics (CFD) validation.
• The method was validated against a single-flagellum model and direct thrust measurements across various Reynolds numbers (Re).

Main Results:

• The PIV-based methodology accurately measured propulsive parameters for microswimmer prototypes.
• Experiments covered low and higher Reynolds numbers (up to Re=0.01), extending previous literature.
• Multi-flagellar configurations showed maximal thrust generation at 0° helical phase-shift but with ~50% lower hydrodynamic efficiency compared to a single flagellum.

Conclusions:

• The developed measurement protocol and static thrust test-bench are suitable for evaluating bio-inspired microscale propulsion.
• Understanding flagellar bundling configurations is crucial for optimizing microswimmer design for thrust and efficiency.