Hydrodynamic coefficients of two fixed circular cylinders fitted with helical strakes at various staggered and tandem arrangements

Experimental results are presented in the paper of two identical stationary cylinders fitted with triple-starting helical strakes subjected to steady uniform cross flows in a flume. The two cylinders were placed at various staggered and tandem positions. In total, 32 relative positions were tested with the streamwise spacing varied 2 to 15 diameters and the transverse spacing from 0 to 7.5 diameters. The hydrodynamic loading was measured in both the in-line and the cross-flow directions for each cylinder. The nominal Reynolds number, based on the cylinder diameter, ranged from 1.40 × 104 to 4.21 × 104. It is found that, as expected, the straked cylinder has a higher drag coefficient in comparison with its smooth counterpart. Qualitatively, the interaction between the two straked cylinders is similar to that between two smooth cylinders in terms of the mean hydrodynamic coefficients. It is further found that whilst the strakes reduce the fluctuating forces on the upstream cylinder, the reduction is significantly smaller for the down-stream straked cylinder.