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|標題:||Experimental study of vortex shedding and subharmonic lock-on for a rotationally oscillating Aat plate|
|期刊/報告no：:||Journal of Wind Engineering and Industrial Aerodynamics, Volume 84, Issue 2, Page(s) 163-180.|
|摘要:||This work investigates the subharmonic lock-on in 1/2 and 1/3 harmonic bands of vortex shedding induced by rotational oscillations of a flat plate normal to a uniform stream in its neutral position. The lock-on boundary, surface pressure and vortical structure of the near wake are also described. In addition, the onset of lock-on, which depends on the combination of the frequency and amplitude of the forcing, is examined by applying spectral analysis of the wake velocity. The forcing frequency is set at a fixed value, in the range 15-120% of the natural shedding frequency of the stationary normal flat plate. Meanwhile, the angular forcing amplitude is varied to determine the lock-on regime. During the subharmonic lock-on, more than one vortex is shed in an oscillation cycle of the plate; each individual vortex influences the base pressure distribution as well. As the lock-on of 1/3 harmonic band is approached at the lower frequency limit, the mean base pressure appears to be uniform along the plate with a level exceeding the unforced plate. For the lock-on of 1/2 harmonic band, the base pressure level reaches a value significantly higher than the unforced plate, i.e. appreciable reduction in drag. Flow visualization suggests that these differences are largely owing to the formation of shed vortex. (C) 2000 Elsevier Science Ltd. All rights reserved.|
|Appears in Collections:||機械工程學系所|
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