Intrinsic characteristics of three-dimensional flow around a wall-mounted conical cylinder

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To investigate the flow characteristics around a wall-mounted conical cylinder, three-dimensional direct numerical simulations are carried out for a conical cylinder with an end diameter ratio ranging from 0.5 to 1.5 at three low Reynolds numbers (Re = 100, 150, 200). The flow features are examined in terms of time-mean streamlines, singularity points location, topological structure, time-mean streamwise vortices, and instantaneous spanwise vortices denoted with different vortex identification methods. The downwash effect also happens even without a free end. The upwash streamlines clash with the downwash streamlines and then coalesce to the saddle (impingement) point P2. The occurrence of the symmetry plane belongs to a new topology, where the saddle point on the bottom wall is an attachment point (NA), instead of the separation point (SS). The singular point verifies the topological existence of the attachment–attachment combination of the horseshoe vortex system. The “Quadrupole Type,” “Sextupole Type,” and “Octupole Type” are identified. The “Octupole Type” is reported first, consisting of a pair of “time-mean streamwise tip vortices,” two pairs of “time-mean streamwise base vortices” and a pair of “time-mean streamwise bottom vortices.” Moreover, the vorticity magnitude cannot represent the occurrence of vortices. The instantaneous iso-surfaces of Q = 0.2 and λ2 = –0.2 in the wake are similar to the threshold of Ω = 0.52. In contrast, the Liutex/Rortex method is easier to identify the streamwise bottom vortices than the former two methods.