Turbulent boundary layer flow over two side-by-side wall-mounted cylinders: Wake characteristics and aerodynamic loads

The distinctive wake characteristics and aerodynamic loads of two side-by-side wall-mounted cylinders were experimentally studied under turbulent boundary layer flows with various gaps. Time-resolved particle image velocimetry was used to analyze the mean and unsteady wake features, whereas a high-resolution load cell was applied to measure the characteristics of lift and drag forces. The results show that the decrease in gap between two cylinders can effectively delay the wake recovery and suppress both the downwash and upwash flows near the top and bottom ends. Overall, with smaller gaps, the turbulence intensity near the top end becomes higher due to the stronger local velocity shear. The distribution of integral time scales indicates that the velocity fluctuations in the near wake region along the middle cylinder span are highly influenced by the local recirculation flows, whereas those near the top end are dominated by the mixing of boundary layer flows. By accounting the equivalent incoming velocity along the cylinder span, both lift and drag coefficient present a similar trend compared to the "infinite length" cylinder cases from previous works. Interestingly, different from cylinders with "infinite length," no clear intermittency of aerodynamic loads was observed in the current work. This can be attributed to the suppression of two-dimensional vortex shedding due to the three-dimensional flow effects and strong background turbulence. The joint distribution of the lift and drag forces reveals that the lift fluctuations increase significantly with the growth of cylinder gaps, whereas that of drag force remains nearly constant.