Numerical simulation on upstream dual rods' effect on aerodynamic characteristics of cylinder

Numerical simulation was constructed to investigate the upstream dual rods' effect on the characteristics of the cylinder at Reynolds number 200. The unsteady laminar model was solved by SIMPLE method with CFD (computational fluid dynamics) commercial software package FLUENT 6.0. When the dual rods have small vertical interval (H/d = 1.1, 1.33), there is only one Karman vortex street formed behind the rods. This case is much more similar to that of a single rod, but the critical spacing ratio for the flow pattern transition is larger than that of the single one. That means there are two different flow patterns with the spacing ratio increase, the cavity flow mode and the wake impinging mode. In the cavity flow mode, the maximum drag and RMS (root mean square) value of lift were reduced by 94% and 79%, respectively. The system drag (including the rod and the cylinder drag) was reduced by 33%. If there are two vortex streets behind the rods with large vertical interval (H/d =3.33, 5.0), the upwind surface of the cylinder is also impinged by the gap flow between the rods, which results in the drag and RMS value of lift reduction is limited.