Wake behind a discontinuous cylinder: unveiling the role of the large scales in wake growth and entrainment

The turbulent flow in the wake of a discontinuous cylinder (DC) was investigated. DC geometry consisted segments $5D$ long (with $D$ being diameter cylinder) separated by gaps width $2.5D$ . Particle image velocimetry and hot-wire anemometry were used to analyse at two Reynolds numbers, $Re = 4000$ $10\,000$ , for $x/D \le 180$ Large eddy simulations both infinite continuous (CC) wakes also carried out 10\,000$ configuration devised trigger shedding horseshoe vortices (HSV) very-near-wake region with intent illustrating role that these three-dimensional HSVs, previously identified far-wake CC, play entrainment process wakes. produced HSVs interaction between high momentum through main spanwise vortex shed behind each segment, while CC they evolve from near-wake instabilities straddled hairpin detach vorticity Kármán vortices. found grow spread transverse direction much faster rate than wake, up until approximately \approx 50$ Prior this location, enhanced growth caused shear-aligned HSV led 3 times maximum mean velocity deficit half.