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ID 119366
Author
Sakai, Hiroshi The University of Tokushima
Oohara, Takeshi The University of Tokushima
Keywords
Mixing layer
Transition
Turbulence
Jet
Shear flow
Oscillating plate
Periodic disturbance
Content Type
Journal Article
Description
The laminar-turbulent transition of a mixing layer excited by oscillating flat plates at an exit of a two-dimensional nozzle was experimentally investigated. The mixing layer was formed between the jet issued from the nozzle and the surrounding quiescent fluid. The plates oscillated vertically in relation to the mean flow. Upper and lower flat plates oscillated anti-symmetrically. The oscillation frequency, 5 Hz, was two orders of magnitude smaller than the fundamental frequency of the velocity fluctuation in the natural transition process. Mean and fluctuating velocity components in the streamwise and normal directions were measured by hot-wire anemometers. The results were compared with the previous case in which the plates oscillated symmetrically. Anti-symmetrical oscillation promoted the expansion of the mixing layer and promoted the disappearance of the potential core more than symmetrical oscillation. The periodic motion of the flow promotes the fluctuation from the time-averaged velocity. The fluctuations from time and phase averages in the anti-symmetrical oscillation were larger than those in the symmetrical oscillation. The contribution of periodic fluctuation disappeared downstream in the symmetrical oscillation but persisted longer in the anti-symmetrical oscillation. In the linear region of the transition, the irregular fluctuation grew exponentially. There were not any differences in the spatial growth rate between the streamwise and normal directions and among three oscillating states. In the nonlinear region, factors other than the temporal fluctuation energy convection and production rates may contribute to the increase in velocity temporal fluctuation in the streamwise component. On the other hand, the convection and production rates may contribute to the increase in velocity fluctuation in the normal component there.
Journal Title
Journal of Fluid Science and Technology
ISSN
18805558
Publisher
日本機械学会
Volume
9
Issue
3
Start Page
JFST0038
Published Date
2014
EDB ID
DOI (Published Version)
URL ( Publisher's Version )
FullText File
language
eng
TextVersion
Author
departments
Science and Technology