Effect of perforation on flow past a conic cylinder at $${\varvec{Re}}~=~100$$ Re = 100 : wavy vortex and sign laws

Mechanism of wavy vortex and sign laws in flow past a bluff body: vortex-induced vortex

“…In the wake of a bluff body without any geometric disturbance, such as a circular-or square-section cylinder, the shedding vortex with the spanwise vorticity ω z is two-dimensional (2-D) and laminar at Re = 40−150 [2], known as Kármán vortex streets. Experiments and numerical simulations confirm that when a geometric disturbance is introduced on a bluff body, the spanwise vortex is wavily distorted across the span, associated to the appearance of additional components of vorticity, ω x and ω y , in the wake [3,4]. This leads to the redistribution of the vorticity field and the formation of different vortex-shedding patterns, such as the Ω-type vortex, and even the complete suppression of Kármán vortices.…”

“…Correspondingly, as shown in Fig. 1b, the vertical interaction between a vertical vortex pair and a spanwise vortex was studied by Lin et al [4] through numerical calculations in the wake of the peak-perforated conic shroud at Re = 100. Similarly, this interaction also results in the spanwise vortices twisted forward and backward in the streamwise direction (i.e.…”

“…Here ω x and ω y can be explained as a result of three-dimensional geometric disturbance or instability, and then are transported into the shear layers and near wake. These additional components of vorticity, ω x and ω y , therefore play an important role in the main vortex-shedding pattern, like the hairpin-like vortex in the wake of a wavy square-section cylinder [13] or thetype vortex in the wake of a straight square-section cylinder [4], in which the head line, "-", denotes the spanwise vortex, while two legs, "| |", denote streamwise and/or vertical vortex pairs shed with this spanwise vortex and elongated by the upstream spanwise vortex of opposite sign.…”

“…On the other hand, through the analysis of three components of vorticity distributed in the near wake of peakperforated conic shroud at Re = 100, an interesting physical phenomenon has been discovered [4]. As shown in Fig.…”

“…b Vertical interaction between a vertical vortex pair and a spanwise vortex flow; this is one of the fundamental and important subjects in vorticity and vortex dynamics [5]. With regard to wavy vortices appearing in the wake of bluff bodies with geometric disturbances, two basic interactions between different vortices have recently been identified and reported [4]. As shown in Fig.…”