Flow and passive scalar transfer characteristics around a row of interacting tandem cylinders

Transfer and transport of a passive scalar as well as flow structures of unbounded flow over a row of 2, 3, 4 and 5 equispaced identical cylinders at Re = 90 and pitch ratios 1.05 D ≤ S ≤ 7 D are investigated. Studies are performed through high fidelity simulations using a novel sharp-interface immersed boundary method. Five flow regimes are identified based on the nature of flow in the gap between the first two cylinders: dormant in the gap where fluid in the gap is motionless; symmetric in the gap where fluid in the gap behaves like a cavity flow; alternating in the gap where fluid in the gap is trapped but flaps up and down; wake in the gap where periodic vortices are shed in the gap; and bi-stable flow regime where vortices are shed in the gap for some time and then quasi-periodic twin vortices prevail for other times. A jump in values of hydrodynamic forces, pressure coefficient, Strouhal number, and Sherwood number is observed as pitch ratio increases due to change in flow structure. At high pitch ratio, a convectively unstable two-row vortical train is formed by the second cylinder. Member cylinders immersed in the two-row vortical structures have no effect on flow structure downstream or upstream and portray poor scalar transfer characteristics. The effect of configuration size on flow structures is found not to be as prominent as that of pitch ratio.