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Advances in Civil Engineering
Volume 2012 (2012), Article ID 523839, 8 pages
http://dx.doi.org/10.1155/2012/523839
Research Article

Unsteady RANS and LES Simulation of an Ideal Rankine Vortex Decay

1Civil Engineering Department, Khulna University of Engineering and Technology, Khulna 9203, Bangladesh
2Department of Urban Management, Kyoto University, Kyoto 615-8540, Japan
3Faculty and Graduate School of Engineering, Hokkaido University, Sapporo 060-8623, Japan

Received 27 July 2011; Revised 7 December 2011; Accepted 3 February 2012

Academic Editor: Ghassan Chehab

Copyright © 2012 Md. Shahjahan Ali et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

The 3D numerical simulation was carried out for an idealized Rankine vortex using nonlinear k-ε model (one kind of RANS model) and large eddy simulation (LES) techniques. In this 3D simulation, the vortex flow field was given to rotate with the vertical axis in a free surface rectangular domain. In order to investigate the predictability of standard (linear) and non-linear k-ε models, the decay of a trailing vortex was simulated and compared with previous DNS data. The governing equations for mean velocities and turbulent flows were discretized with the finite volume method based on a staggered grid system. It was observed that in the growth phase as well as in stabilized phase of turbulence, the decay rate of tangential velocity by RANS model was well comparable with LES simulation as well as previous DNS data. However, in the decay phase of turbulence, RANS model showed slightly faster decay of tangential velocity due to its slower decay of turbulence compared to LES or DNS. The patterns as well as magnitudes of secondary currents predicted by RANS and LES models were well comparable to each other.