Transitions in the wake of a flapping foil

transitions_wakeTransitions in the wake of a flapping foil
R. Godoy-Diana; J. L. Aider & J. E. Wesfreid.
Physical Review E, 77 : 016308 (2008).

Abstract: We study experimentally the vortex streets produced by a flapping foil in a hydrodynamic tunnel, using two-dimensional particle image velocimetry. An analysis in terms of a flapping frequency-amplitude phase space allows the identification of (i) the transition from the well-known Bénard-von Kármán (BvK) wake to the reverse BvK vortex street that characterizes propulsive wakes, and (ii) the symmetry breaking of this reverse BvK pattern giving rise to an asymmetric wake. We also show that the transition from a BvK wake to a reverse BvK wake precedes the actual drag-thrust transition and we discuss the significance of the present results in the analysis of flapping systems in nature. Exploring the frequency-amplitude parameter space allows for the observation of a wide variety of vortex geometries in the wake of the flapping foil (see figure below).

Vortices in the wake of a flapping foil


  author = {{G}odoy-{D}iana, {R}. and {A}ider, {J}. {L}. and {W}esfreid, {J}. {E}.},
  title = {Transitions in the wake of a flapping foil},
  journal = {Physical Review E},
  year = {2008},
  volume = {77},
  pages = {016308}