DNS of squirmers (spherical microswimmers) with rotlet*

The squirmer model introduced by Lighthill and later extended by Blake allows the description of microorganisms such as algae and bacteria. It consists in a spherical particle with a prescribed tangential surface velocity, neglecting the radial component, responsible for the self-propulsion. If the microorganism repels fluid along its axis and repels it to the sides it is called pusher (like the bacterium Escherichia Coli); in the opposite case it is called puller (like the alga Chlamydomonas Reinardtii). In this study the squirmer model is incorporated into the Smoothed Profile Method, an efficient DNS scheme to simulate solid objects into a fluid taking fully into account the hydrodynamics, which has already been successfully used in the past to study collective motion and interactions of squirmers. Now the traditional squirmers (pusher and puller) are modified by introducing a rotlet term, an azimuthal component of surface velocity to give a more realistic description of the motion of microorganisms like bacteria whose flagellar and body rotate in the opposite direction.