Anomalous hydrodynamic drafting of interacting flapping flags

Leif Ristroph, Jun Zhang

Research output: Contribution to journalArticlepeer-review


In aggregates of objects moving through a fluid, bodies downstream of a leader generally experience reduced drag force. This conventional drafting holds for objects of fixed shape, but interactions of deformable bodies in a flow are poorly understood, as in schools of fish. In our experiments on "schooling" flapping flags, we find that it is the leader of a group who enjoys a significant drag reduction (of up to 50%), while the downstream flag suffers a drag increase. This counterintuitive inverted drag relationship is rationalized by dissecting the mutual influence of shape and flow in determining drag. Inverted drafting has never been observed with rigid bodies, apparently due to the inability to deform in response to the altered flow field of neighbors.

Original languageEnglish (US)
Article number194502
JournalPhysical Review Letters
Issue number19
StatePublished - Nov 3 2008

ASJC Scopus subject areas

  • General Physics and Astronomy


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