This article has been retracted by the Editor of the Journal of Fluid Mechanics and Cambridge University Press. Following publication, the Editor carried out an assessment of the article’s references. That assessment established that a substantial number of the sources cited in the article and listed in its reference list do not correspond to identifiable published works: several cited journal articles could not be located in the journals, volumes, or pages given, or in the publication records of the authors to whom they are attributed, and further entries assign genuine works to incorrect journals, volumes, or pages. Because these references cannot be verified as existing publications, the Editors have concluded that the evidentiary basis for the article’s analysis and conclusions is unreliable, and that the integrity of the scholarly record requires retraction rather than correction.

This retraction has been issued in accordance with the guidelines of the Committee on Publication Ethics (COPE). The authors agree with the retraction. The online version of the article has been retained and watermarked ‘Retracted.’