Journal of Fluid Mechanics



Quantitative measurements of three-dim ensional structures in the wake of a circular cylinder


Hussein Mansy a1, Pan-Mei Yang a1 and David R. Williams a1
a1 Mechanical and Aerospace Engineering Department, Illinois Institute of Technology, Chicago, IL 60616, USA

Article author query
mansy h   [Google Scholar] 
yang pm   [Google Scholar] 
williams dr   [Google Scholar] 
 

Abstract

The fine scale three-dimensional structures usually associated with streamwise vortices in the near wake of a circular cylinder have been studied at Reynolds numbers ranging from 170 to 2200. Spatially continuous velocity measurements along lines parallel to the cylinder axis were obtained with a scanning laser anemometer. To detect the streamwise vortices in the amplitude modulated velocity field, it was necessary to develop a spatial decomposition technique to split the total flow into a primary flow component and a secondary flow component. The primary flow is comprised of the mean flow and Strouhal vortices, while the secondary flow is the result of the three-dimensional streamwise vortices that are the essence of transition to turbulence. The three-dimensional flow amplitude increases in the primary vortex formation region, then saturates shortly after the maximum amplitude in the primary flow is reached. In the near-wake region the wavelength decreases approximately like Re−0.5, but increases with downstream distance. A discontinuous increase in wavelength occurs below Re = 300 suggesting a fundamental change in the character of the three-dimensional flow. At downstream distances (x/D = 10-20), the spanwise wavelength decreases from 1.42D to 1.03D as the Reynolds number increases from 300 to 1200.

(Published Online April 26 2006)
(Received July 29 1993)
(Revised January 7 1994)



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