Energy extraction from a pitching airfoil

Physics of Fluids, Journal Year: 2025, Volume and Issue: 37(4)

Published: April 1, 2025

This paper experimentally investigates the effects of various oscillation parameters on energy extraction efficiency a National Advisory Committee for Aeronautics 0015 airfoil in forced pitching motion about its quarter-chord at Reynolds number 80 000. The reduced frequency, k, amplitude, A, and mean angle attack, αmean, are systematically varied, pressure distribution around center-span is recorded. Flow visualization used to reveal vortex dynamics. highest cycle-averaged achieved 0.24%, k=0.480, A=10°, αmean=18°; this case, two large vortices formed, with primary detaching from leading edge as attack maximum, such that resulting low near trailing coincides downstroke. All cases experience negative most upstroke, which associated flow reattachment along airfoil's upper surface. A framework understand impact dynamics proposed, divides surface into quadrants based time position relative axis. Increasing k both cause delay formation detachment vortex. αmean results significant changes flow, no being formed angles (below static stall angle) higher (above angle).

Language: Английский

Low-speed aeroelastic interactions in tandem flags under streamlined and bluff-body wake flows

Physics of Fluids, Journal Year: 2025, Volume and Issue: 37(4)

Published: April 1, 2025

This study examines the aeroelastic interactions of triangular steel flags in tandem configuration for flow speed (U) up to 9.0 m/s, with inter-flag gap (Gf) ranging from 0.1 5 times leading flag's characteristic length (L). The flag is subjected both streamlined and vortex-induced flows (VIFs). Wind tunnel experiments reveal a subcritical bifurcation route limit cycle oscillations (LCOs) under flow, while VIF alters supercritical route. First, identical natural frequency 3.59 Hz (first bending mode) flutter near 7.4 m/s are tested flow. dynamics remains largely unchanged compared its standalone dynamics, trailing response highly sensitive position wake flag. Phase including locking bounded phase differences, emerges at different regimes depicting synergistic destructive coherence. For closely spaced (Gf = 0.1L), LCO amplitudes suppressed by 50%, larger gaps, increase 1.5 times. non-identical much higher (5.48 Hz) onset (U> m/s), advanced matches that oscillates close across wide range gaps speeds but exhibits small-amplitude LCOs driven very low speeds. Finally, placed downstream cylindrical bluff body examine impact conditions. Small-amplitude aperiodic observed below critical speed, which, turn, induce sufficiently strong trigger transitions periodic speeds, strongly oscillations, one locked comprehensive nonlinear analysis presented can be utilized enhancing multi-flag energy harvesting, fluid mixing, heat transfer.

Language: Английский