Purcell's Swimmer Revisited

Purcell's swimmer was proposed by E. M. Purcell to explain bacterial swimming motions. It has been proved experimentally that a swimmer of this kind is possible under inertial-less and high viscous environment. But we could not investigate all the aspects of this mechanism through experiments due to practical difficulties. The computational fluid dynamics (CFD) provides complementary methods to experimental fluid dynamics. In particular, these methods offer the means of testing theoretical advances for conditions unavailable experimentally. Using such methodology, we have investigated the fluid dynamics of force production associated with the Purcell's swimmer. By employing dynamic mesh and user-defined functions, we have computed the transient flow around the swimmer for various stroke angles. Our simulations capture the bidirectional swimming property successfully and are in agreement with existing theoretical and experimental results. To our knowledge, this is the first CFD study which shows the fact that swimming direction depends on stroke angle. We also prove that for small flapping frequencies, swimming direction can also be altered by changing frequency-showing breakdown of Stokes law with inertia.