Journal of Fluid Mechanics



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On low-frequency modulations and three-dimensionality in vortex shedding behind a normal plate


S. J. WU a1, J. J. MIAU a1c1, C. C. HU a1 and J. H. CHOU a2
a1 Department of Aeronautics and Astronautics, National Cheng-Kung University, Tainan, Taiwan 70101
a2 Department of Engineering Science, National Cheng-Kung University, Tainan, Taiwan 70101

Article author query
wu sj   [Google Scholar] 
miau jj   [Google Scholar] 
hu cc   [Google Scholar] 
chou jh   [Google Scholar] 
 

Abstract

In this study spanwise correlation measurements and smoke flow visualization were performed on vortex shedding behind a normal plate. For Reynolds numbers in a range between 1800 and 27000, the hot-wire signals measured were analysed by a wavelet transformation, from which the instantaneous properties of vortex shedding were obtained and examined. Results show that the phase difference of vortex shedding detected at two spanwise locations, separated by twice the characteristic length, can be as high as 35$^\circ$. A correlation analysis further shows that large spanwise phase differences occur when small fluctuating amplitudes in the vortex shedding signals are measured. Smoke-wire visualization performed at Reynolds number 1800 indicates that the formation of shedding vortex can be divided into two distinct situations, namely, one featuring a long formation region, called Mode L; and the other featuring a short formation region, called Mode S. In Mode S, the three-dimensionality of vortex formation appears to be very pronounced, and the secondary vortices are clearly present in the separated shear layer. The events of Mode S occupy less than 5% of the total time measured, and are called the burst events in this study.

(Received December 10 2003)
(Revised October 1 2004)


Correspondence:
c1 Author to whom correspondence should be addressed: jjmiau@mail.ncku.edu.tw


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