Near-wake flow characteristics of two side-by-side circular cylinders close to a wall

Flow characteristics in the near wake of two identical side-by-side circular cylinders located close to a fully developed turbulent boundary layer are investigated experimentally using the particle image velocimetry (PIV) and the pressure sensor. The Reynolds number based on the cylinder diameter (D) is 1,696, the boundary layer thickness is 6.6 D, the cylinder center-to-center spacing (T) is varied from T/D = 1 to 1.906, and the gap spacing between the lower cylinder and the wall (G) is varied from G/D = 0 to 1.811. To study the effects of changing the gap ratios of T/D and G/D on the wake flow, various wake characteristics such as averaged streamlines, Reynolds stress and vorticity contours as well as other key flow features including the length scales and the Strouhal number are investigated for different ratios of T/D and G/D. According to these wake characteristics, five basic flow patterns have been identified.