Numerical simulations of steady flow past two cylinders in staggered arrangements

This paper presents a numerical study on steady flow around two identical circularcylinders of various arrangements at a low subcritical Reynolds number (Re =10³).The ratio of centre-to-centre pitch distance (P) to the diameter of the cylinder (D)ranges from 1.5 to 4, and the alignment angle (a) between the two cylinders andthe direction of the cross-flow varies from 0 to 90. The detailed flow informationobtained from direct numerical simulation allows a comprehensive interpretation ofthe underlying physics responsible for some interesting flow features observed aroundtwo staggered cylinders. Four distinct vortex shedding regimes are identified and itis demonstrated that accurate classification of vortex shedding regimes around twostaggered cylinders should consider the combination of the flow visualization with theanalyses of lift forces and velocity signal in the wake. It is revealed that the change inpressure distribution, as a result of different vortex shedding mechanisms, leads to avariety of characteristics of hydrodynamic forces on both cylinders, including negativedrag force, attractive and repulsive lift forces. Two distinct vortex shedding frequenciesare identified and are attributed to the space differences based on the flow structuresobserved in the wake of the cylinders. It is also found that the three-dimensionality offlow in the gap and the shared wake region is significantly weakened in almost two ofthe classified flow regimes; however, compared with the flow around a single cylinder,active wake interaction at large a does not clearly increase the three-dimensionality.