Pumping, mixing, and swimming with oscillating arms*

At microscopic scales, it is not trivial to generate and manipulate flow due to the dominant effects of viscosity. Here we demonstrate in table-top experiments how a simple oscillatory motion of rigid arms with phase delay can produce complex flow patterns at low Reynolds number.  The experiments are in good agreement with simulations performed using the regularized Stokeslets method. The resultant flow enables mixing of the surrounding fluid, manipulation of large objects at a distance, and locomotion of mobile bodies. This could inspire new designs for pumps, mixers, and robotic swimmers at the microscopic scale.