Numerical investigation of flow around an inline square cylinder array with different spacing ratios

Flow around an inline cylinder array consisting of six square cylinders at a Reynolds number of 100 is investigated numerically by using a second-order characteristic-based split finite element algorithm in this paper. The numerical method and the code for the solution of incompressible Navier-Stokes equations are validated for the flow past a single and two tandem square cylinders, and the numerical results show a good agreement with the available literatures. The study then focuses on the effect of spacing ratio (ratio of center-to-center distance s to cylinder width d, widely ranging in s/d = 1.5-15.0) on flow characteristics by identifying flow patterns and extracting pressure distributions, force statistics as well as wake oscillation frequencies. Numerical results showed six different flow patterns, which appeared successively with the increase of gap spacing, namely, steady wake, non-fully developed vortex street in single row and double-row, fully developed vortex street in double-row, fully developed vortex street in partially recovered single-row and fully developed multiple vortex streets. A shielding effect of the first cylinder and reducing Bernoulli effect on the rear cylinder rows work in the pressure distribution even at very large gap spacing. In the vortex shedding regime, beyond the critical spacing of wake mode transition, force statistics show a periodic variation characteristic for the last four cylinders; moreover, multiple frequency components involve in the vortex shedding oscillation behind these cylinders and the dominant frequency jumps down with the increase of the spacing. Finally, the flow fields around the critical spacing range are comprehensively analyzed to reveal the crucial mechanism behind the observed aerodynamic characteristics. (C) 2011 Elsevier Ltd. All rights reserved.