TY - GEN
T1 - Unsteady propulsion and wake structure of a finite aspect ratio piching plate
AU - Buchholz, James
AU - Smits, Alexander J.
PY - 2007
Y1 - 2007
N2 - 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.
AB - 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.
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M3 - Conference contribution
AN - SCOPUS:34250807264
SN - 1563478900
SN - 9781563478901
T3 - Collection of Technical Papers - 45th AIAA Aerospace Sciences Meeting
SP - 1457
EP - 1470
BT - Collection of Technical Papers - 45th AIAA Aerospace Sciences Meeting
T2 - 45th AIAA Aerospace Sciences Meeting 2007
Y2 - 8 January 2007 through 11 January 2007
ER -