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A laser-Doppler velocimetry study of ensemble-averaged characteristics of the turbulent near wake of a square cylinder

Published online by Cambridge University Press:  26 April 2006

D. A. Lyn ,
S. Einav ,
W. Rodi  and
J.-H. Park
D. A. Lyn
Affiliation:
School of Civil Engineering, Purdue University, W. Lafayette, IN 47907, USA
S. Einav
Affiliation:
Faculty of Engineering, Tel Aviv University, Tel Aviv 69978, Israel
W. Rodi
Affiliation:
Institute for Hydromechanics, Universität. Karlsruhe, D-7500 Karlsruhe, Germany
J.-H. Park
Affiliation:
Chungnam National University, Taejon, Korea
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Abstract

Ensemble-averaged statistics at constant phase of the turbulent near-wake flow (Reynolds number ≈ 21400 around a square cylinder have been obtained from two-component laser-Doppler measurements. Phase was defined with reference to a signal taken from a pressure sensor located at the midpoint of a cylinder sidewall. The distinction is drawn between the near wake where the shed vortices are ‘mature’ and distinct and a base region where the vortices grow to maturity and are then shed. Differences in length and velocity scales and vortex celerities between the flow around a square cylinder and the more frequently studied flow around a circular cylinder are discussed. Scaling arguments based on the circulation discharged into the near wake are proposed to explain the differences. The relationship between flow topology and turbulence is also considered with vorticity saddles and streamline saddles being distinguished. While general agreement with previous studies of flow around a circular cylinder is found with regard to essential flow features in the near wake, some previously overlooked details are highlighted, e.g. the possibility of high Reynolds shear stresses in regions of peak vorticity, or asymmetries near the streamline saddle. The base region is examined in more detail than in previous studies, and vorticity saddles, zero-vorticity points, and streamline saddles are observed to differ in importance at different stages of the shedding process.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 304 , 10 December 1995 , pp. 285 - 319
Copyright
© 1995 Cambridge University Press

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