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A combined direct numerical simulation–particle image velocimetry study of the turbulent near wake

Published online by Cambridge University Press:  15 November 2006

S. DONG
Affiliation:
Division of Applied Mathematics, Brown University, Providence, RI 02912, USA Present address: Center for Computational and Applied Mathematics, Department of Mathematics, Purdue University, West Lafayette, IN47907, USA.
G. E. KARNIADAKIS
Affiliation:
Division of Applied Mathematics, Brown University, Providence, RI 02912, USA
A. EKMEKCI
Affiliation:
Department of Mechanical Engineering, Lehigh University, Bethlehem, PA 18015, USA
D. ROCKWELL
Affiliation:
Department of Mechanical Engineering, Lehigh University, Bethlehem, PA 18015, USA

Abstract

We investigate the near wake of a cylinder at values of Reynolds number corresponding to the onset and development of shear-layer instabilities. By combining quantitative experimental imaging (particle image velocimetry, PIV) and direct numerical simulations at $Re \,{=}\, 3900/4000$ and 10000, we show that the flow structure is notably altered. At higher Reynolds number, the lengths of both the wake bubble and the separating shear layer decrease substantially. Corresponding patterns of velocity fluctuations and Reynolds stress contract towards the base of the cylinder. The elevated values of Reynolds stress at upstream locations in the separated layer indicate earlier onset of shear-layer transition. These features are intimately associated with the details of the shear-layer instability, which leads to small-scale vortices. The simulated signatures of the shear-layer vortices are characterized by a broadband peak at $Re \,{=}\, 3900$ and a broadband high spectral-density ‘plateau’ at $Re \,{=}\, 10\,000$ in the power spectra. The shear-layer frequencies from the present direct numerical simulations study agree well with previous experimentally measured values, and follow the power law suggested by other workers.

Type
Papers
Copyright
© 2006 Cambridge University Press

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