Three-dimensional wake transition for a circular cylinder near a moving wall. (5th April 2017)

• Record Type: Journal Article
• Authors: Jiang, Hongyi; Cheng, Liang; Draper, Scott; An, Hongwei
• Is Part Of: Journal of fluid mechanics. Volume 818(2017)
• Page Start: 260
• Page End: 287
• Publication Date: 2017-04-05
• Subjects: vortex instability, -- vortex streets, -- wakes; Fluid mechanics -- Periodicals; 532.005
• DOI: 10.1017/jfm.2017.146
• Languages: English
• ISSNs: 0022-1120

Abstract

Abstract : Three-dimensional (3D) wake transition for a circular cylinder placed near to a moving wall is investigated using direct numerical simulation (DNS). The study covers a parameter space spanning a gap ratio $(G/D)\geqslant 0.3$ and Reynolds number ( $Re$ ) up to 325. The wake transition regimes in the parameter space are mapped out. It is found that vortex dislocation associated with Mode A is completely suppressed at $G/D$ smaller than approximately 1.0. The suppression of vortex dislocation is believed to be due to the confinement of the Mode A streamwise vortices by the plane wall, which suppresses the excess growth and local dislocation of any Mode A vortex loop. Detailed wake transition is examined at $G/D=0.4$, where the wake transition sequence is 'two-dimensional (2D) $\rightarrow$ ordered Mode A $\rightarrow$ mode swapping (without dislocations) $\rightarrow$ Mode B'. Relatively strong three-dimensionality is found at $Re=160{-}220$ as the wake is dominated by large-scale structure of ordered Mode A, and also at $Re\geqslant 285$, where Mode B becomes increasingly disordered. A local reduction in three-dimensionality is observed at $Re=225{-}275$, where the wake is dominated by finer-scale structure of a mixture of ordered Modes A and B. Corresponding variations in the vortex shedding frequency and hydrodynamic forces are also investigated.