Three-dimensional structure of longitudinal vortices shedding from cruciform two-cylinder systems with different geometries

Abstract

Abstract: In previous research the present authors have shown that cross flow vibrations can be induced on a cylinder by setting another cylindrical body downstream in cruciform arrangement with a certain gap s between them. These vibrations are excited by two longitudinal vortices (LVs), i.e. the trailing vortex (TV) and the necklace vortex (NV), shedding periodically near the cross of the system. In this study, LVs shedding from three cruciform systems, i.e. circular-cylinder/circular-cylinder (CC/CC), circular-cylinder/strip-plate (CC/SP) and square-cylinder/strip-plate (SC/SP) system, are observed from three directions using water tunnel and surface-die-streak technique to clarify their three-dimensional structure. The gap-to-diameter ratio s/d is set at 0.08 or 0.28 as the representative values of TV and NV, respectively. Formation of TV or NV depends on the system geometry s/d and Reynolds number Re. In the case of CC/CC, TV is formed at s/d = 0.08 and NV at s/d = 0.28 steadily when 1400 ≤ Re ≤ 2000, and they shed periodically when 3300 ≤ Re ≤ 5700. In the case of CC/SP, steady shedding of TV is observed at the both values of s/d in the lower Re range and periodic shedding is observed only for TV at s/d = 0.08 in the higher Re range, but with poorer periodicity. In the case of SC/SP, NV is formed at the both values of s/d and periodic shedding is not observed up to the highest value of Re = 5000 in this experiment.