摘要
A new type of propeller that is optimized for low Reynolds numbers is required to propel a small object in a medium where the flow is dominated by viscous rather than inertial forces. A propeller in the shape of a bacterial flagellum seems an appro- priate choice for driving a small object. Accordingly, in this study, we visualized the velocity field induced by a spring-like propeller inspired by the Escherichia coli flagellum, using a macroscopic model and applying stereoscopic particle image velocimetry. We also experimentally evaluated the effect of pitch and rotational speed on the performance of this flagellar propeller. Silicone oil, which has a kinematic viscosity 100,000 times that of water, was used as the working fluid to generate a low Reynolds number for the macroscopic model. Thrust, torque, and velocity were measured as functions of pitch and rota- tional speed, and the efficiency of the propeller was calculated from the measured results. We found that the flagellar propeller reached a max!mum efficiency when the pitch angle was approximately 53°. Compared to pitch, rotational speed had a relatively small effect on the efficiency, and the pitch altered the flow pattern behind the rotating propeller.
A new type of propeller that is optimized for low Reynolds numbers is required to propel a small object in a medium where the flow is dominated by viscous rather than inertial forces. A propeller in the shape of a bacterial flagellum seems an appro- priate choice for driving a small object. Accordingly, in this study, we visualized the velocity field induced by a spring-like propeller inspired by the Escherichia coli flagellum, using a macroscopic model and applying stereoscopic particle image velocimetry. We also experimentally evaluated the effect of pitch and rotational speed on the performance of this flagellar propeller. Silicone oil, which has a kinematic viscosity 100,000 times that of water, was used as the working fluid to generate a low Reynolds number for the macroscopic model. Thrust, torque, and velocity were measured as functions of pitch and rota- tional speed, and the efficiency of the propeller was calculated from the measured results. We found that the flagellar propeller reached a max!mum efficiency when the pitch angle was approximately 53°. Compared to pitch, rotational speed had a relatively small effect on the efficiency, and the pitch altered the flow pattern behind the rotating propeller.
