Response of a savonius rotor to unsteady flow

A Savonius rotor used as a speed measuring device was subjected to a unidirectional unsteady flow having a mean value U0. A comparison between the rotor rotation rate in this unsteady flow and its rotation rate in a steady flow U0 yielded systematic errors in velocities as inferred from steady-state calibrations. Further dependence of the errors on dimensional quantities suggests that pr esent attempts to model the Savonius rotor\u27s dynamics will have to be expanded

Separation of suspended particles in microfluidic systems by directional-locking in periodic fields

We investigate the transport and separation of overdamped particles under the action of a uniform external force in a two-dimensional periodic energy landscape. Exact results are obtained for the deterministic transport in a square lattice of parabolic, repulsive centers that correspond to a piecewise-continuous linear-force model. The trajectories are periodic and commensurate with the obstacle lattice and exhibit phase-locking behavior in that the particle moves at the same average migration angle for a range of orientation of the external force. The migration angle as a function of the orientation of the external force has a Devil's staircase structure. The first transition in the migration angle was analyzed in terms of a Poincare map, showing that it corresponds to a tangent bifurcation. Numerical results show that the limiting behavior for impenetrable obstacles is equivalent to the high Peclet number limit in the case of transport of particles in a periodic pattern of solid obstacles. Finally, we show how separation occurs in these systems depending on the properties of the particles