Transition of Flow Past Five Square Obstacles in Tandem Arrangement at Distinct Gap Spacing

Abstract

A two-dimensional (2-D) numerical simulation was performed for the flow past five square obstacles of similar size ‘D’ aligned inline at  fixed Reynolds number Re = 150 to investigate the transition in flow behavior. The gap spacing (gc = s/D) between the obstacles was varied from gc = 0.25 to 5. The results were obtained in terms of vorticity contour visualization, time-history analysis of drag (Cd) and lift (Cl) forces, and physical parameters. Four different flow modes were identified under the effect of gap spacing (gc = s/d). These are: i) Shear layer flow mode ii) Half-developed irregular vortex shedding flow mode iii) Fully-developed two-row vortex shedding flow mode iv) Two-row single bluff body flow mode for obstacles C1-C5. The values of Cdmean, Cdrms, Clrms, and St were calculated for physical parameters. Cdmean exhibited a mixed trend with increasing gap spacing for obstacles C3, C4, and C5. The highest value of Cdmean was observed at gc = 5 for obstacle C1, which was 1.4594, while the smallest value was attained for obstacle C3 at gc = 0.25. There were also some negative values of Cdmean for obstacle C2 at gc = 0.25 - 2.25 and for obstacle C3 at gc = 0.25 - 1.25 due to the effect of pressure, known as thrust. Furthermore, the Strouhal number showed an increasing trend for both small and large gap spacings, i.e., gc = 0.25 - 0.75 and gc = 1.5 – 5. The highest value of the Strouhal number was observed at gc = 5 for obstacle C5, which was 0.1521.