Three-dimensional wake transition for a circular cylinder near a moving wall

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 and Reynolds number 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 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 , where the wake transition sequence is 'two-dimensional (2D) ordered Mode A mode swapping (without dislocations) Mode B'. Relatively strong three-dimensionality is found at as the wake is dominated by large-scale structure of ordered Mode A, and also at Re ≤285, where Mode B becomes increasingly disordered. A local reduction in three-dimensionality is observed at , 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.