Experimental investigation of flow characteristics around tandem arrangement of triangular and square cylinders

The paper presents an experimental investigation of the flow around two bluff bodies in a tandem arrangement. Two different configurations were investigated. The first one concerns two square cylinders (SS case) whereas in the second setup, a triangular cylinder was used as an upstream object (TS case). Particular attention was devoted to examining the effect of the gap space $G$ between cylinders (from 1 to 6) on the flow structure and dynamics of vortices. The study also includes measurements conducted for single square and single triangular cylinders to show how the second object modifies the flow field. It was found that the wake behind each object is always wider for the SS case regardless of $G$. When $G$ is less than or equal to 3 for the TS case, the slender body regime is seen in the flow field which for the SS case is normally present for $G<1.5$. Consequently, distinctive vortex shedding frequencies cannot be distinguished in the gap for the TS case when $G\le 3$. When $G\ge 4$, twice as high values of the Strouhal number $St$ are reported in the gap for the TS case compared to the SS case. Downstream the second object, $St$ gradually decreases from $\sim$0.245 to $\sim$1.14 with increasing $G$ from 1 to 4 for the TS case, whereas for $5\le G\le 6$ distinctive vortex shedding frequencies are no longer observed.