Particle image velocimetry technique measurements of the near wake behind a cylinder-pair of unequal diameters

The wake structure behind a circular cylinder-pair of unequal diameters as a function of incident flow angle alpha (0 degrees <= alpha <= 180 degrees) has been investigated using the particle image velocimetry technique. The Reynolds number Re, center-to-center spacing ratio (P/D) and diameter ratio (d/D) are kept constant at 1200, 1.2 and 2/3, respectively. Instantaneous vorticity contours, mean flow fields and Reynolds shear stress contours are presented to elucidate the flow characteristics. The flow patterns behind the cylinder-pair change from that of a single bluff body to two vortex streets with increasing incident angle over the range of 0 degrees <= alpha <= 90 degrees, while the inverse phenomenon is observed when 90 degrees < alpha <= 180 degrees.