Unsteady propulsion and wake structure of a finite aspect ratio piching plate

James Buchholz, Alexander J. Smits

Research output: Chapter in Book/Report/Conference proceedingConference contribution


Thrust performance and wake structure were investigated for a rigid rectangular panel pitching about its leading edge in a free stream. Thrust coefficient was found to depend primarily on Strouhal number St and the aspect ratio of the panel S/C. Propulsive efficiency was sensitive to aspect ratio only for S/C less than 0.83; however, the magnitude of the peak efficiency of a given panel with variation in Strouhal number varied inversely with the amplitude to span ratio A/S, while the Strouhal number of optimum efficiency increased with increasing A/S. Peak efficiencies between 9% and 21% were measured. Wake structures corresponding to a subset of the thrust measurements were investigated using dye visualization and Digital Particle Image Velocimetry. In general, the wakes divided into two oblique jets; however, when operating at or near peak efficiency, the near wake in many cases represented a von Kármán vortex street with the signs of the vortices reversed. The three-dimensional structure of the wakes were investigated in detail for S/C = 0.54, A/S -0.31, ReC = 640. Three distinct wake structures were observed with variation in Strouhal number. For approximately 0.20 < St < 0.25, the main constituent of the wake was a horseshoe vortex shed by the tips and trailing edge of the panel. Streamwise variation in the circulation of the streamwise horseshoe legs was consistent with a spanwise shear layer bridging them. For St > 0.25, a reorganization of some of the spanwise vorticity yielded a bifurcating wake formed by trains of vortex rings connected to the tips of the horseshoes. For St > 0.5 an additional structure formed from a perturbation of the streamwise leg which caused a spanwise expansion. The wake model paradigm established here is consistent with structures observed for a wide variety of unsteady flows.

Original languageEnglish (US)
Title of host publicationCollection of Technical Papers - 45th AIAA Aerospace Sciences Meeting
Number of pages14
StatePublished - 2007
Event45th AIAA Aerospace Sciences Meeting 2007 - Reno, NV, United States
Duration: Jan 8 2007Jan 11 2007

Publication series

NameCollection of Technical Papers - 45th AIAA Aerospace Sciences Meeting


Other45th AIAA Aerospace Sciences Meeting 2007
Country/TerritoryUnited States
CityReno, NV

All Science Journal Classification (ASJC) codes

  • Space and Planetary Science
  • Aerospace Engineering


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