Characterization of azimuthal and radial velocity fields induced by rotors in flows with a low Reynolds number

摘要

We theoretically and experimentally investigate the flow field that emergesfrom a rod-like microrotor rotating about its center in a non-axisymmetricmanner. A simple theoretical model is proposed that uses a superposition of tworotlets as a fundamental solution to the Stokes equation. The predictions ofthis model are compared to measurements of the azimuthal and radialmicrofluidic velocity field components that are induced by a rotor composed offused microscopic spheres. The rotor is driven magnetically and the fluid flowis measured with the help of a probe particle fixed by an optical tweezer. Wefind considerable deviations of the mere azimuthal flow pattern induced by asingle rotating sphere as it has been reported by Di Leonardo \textit{et al.}[Phys. Rev. Lett. 96, 134502 (2006)]. Notably, the presence of a radialvelocity component that manifests itself by an oscillation of the probeparticle with twice the rotor frequency is observed. These findings open up away to discuss possible radial transport in microfluidic devices.