Time-resolved vortex wake of a common swift flying over a range of flight speeds

P. Henningsson*, F.T. Muijres, A. Hedenström

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

41 Citations (Scopus)


The wake of a freely flying common swift (Apus apus L.) is examined in a wind tunnel at three different flight speeds, 5.7, 7.7 and 9.9 m s-1. The wake of the bird is visualized using high-speed stereo digital particle image velocimetry (DPIV). Wake images are recorded in the transverse plane, perpendicular to the airflow. The wake of a swift has been studied previously using DPIV and recording wake images in the longitudinal plane, parallel to the airflow. The high-speed DPIV system allows for time-resolved wake sampling and the result shows features that were not discovered in the previous study, but there was approximately a 40 per cent vertical force deficit. As the earlier study also revealed, a pair of wing-tip vortices are trailing behind the wingtips, but in addition, a pair of tail vortices and a pair of 'wing root vortices' are found that appear to originate from the wing/body junction. The existence of wing root vortices suggests that the two wings are not acting as a single wing, but are to some extent aerodynamically detached from each other. It is proposed that this is due to the body disrupting the lift distribution over the wing by generating less lift than the wings.

Original languageEnglish
Pages (from-to)807-816
JournalJournal of the Royal Society Interface
Issue number59
Publication statusPublished - 17 Nov 2010
Externally publishedYes


  • Aerodynamics
  • Apus apus
  • Common swift
  • Particle image velocimetry (DPIV)
  • Wake
  • Wind tunnel

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