Two- and three-dimensional instabilities in the wake of a circular cylinder near a moving wall. (5th January 2017)

• Record Type: Journal Article
• Authors: Jiang, Hongyi; Cheng, Liang; Draper, Scott; An, Hongwei
• Is Part Of: Journal of fluid mechanics. Volume 812(2017)
• Page Start: 435
• Page End: 462
• Publication Date: 2017-01-05
• Subjects: vortex instability, -- vortex shedding, -- wakes; Fluid mechanics -- Periodicals; 532.005
• DOI: 10.1017/jfm.2016.810
• Languages: English
• ISSNs: 0022-1120

Abstract

Abstract : Two-dimensional (2D) and three-dimensional (3D) instabilities in the wake of a circular cylinder placed near to a moving wall are investigated using direct numerical simulation (DNS). The study covers a parameter space spanning a non-dimensional gap ratio ( $G^{\ast }$ ) between 0.1 to 19.5 and Reynolds number ( $Re$ ) up to 300. Variations in the flow characteristics with $Re$ and $G^{\ast }$ are studied, and their correlations with the hydrodynamic forces on the cylinder are investigated. It is also found that the monotonic increase of the critical $Re$ for 2D instability ( $Re_{cr2D}$ ) with decreasing $G^{\ast }$ is influenced by variations in the mean flow rate around the cylinder, the confinement of the near-wake flow by the plane wall and the characteristics of the shear layer formed above the moving wall directly below the cylinder. The first factor destabilizes the wake flow at a moderate $G^{\ast }$ while the latter two factors stabilize the wake flow with decreasing $G^{\ast }$ . In terms of 3D instability, the flow transition sequence of '2D steady $\rightarrow$ 3D steady $\rightarrow$ 3D unsteady' for small gap ratios is analysed at $G^{\ast }=0.2$ . It is found that the 3D steady and 3D unsteady flows are triggered by Mode C instability due to wall proximity. However, the Mode C structure is not sustained indefinitely, since interference with the shear layer leads to other 3D steady and unsteady flow structures.