Abstract
The wake of an elliptical cylinder at low incident angles is investigated for different aspect ratio cylinders using stability analysis and direct simulations. In particular, two and threedimensional transitions are mapped for cylinders of aspect ratios between 1 and 4 using Floquet stability analysis. The transition scenario for nearunity aspect ratio cylinders resembles that for a circular cylinder wake as Reynolds number is increased to ; first, with the transition from steady twodimensional flow to unsteady twodimensional flow, followed by the onset of threedimensional flow via a longwavelength instability (mode A), then, a shortwavelength instability (mode B) and, finally, an intermediary wavelength instability which is quasiperiodic in nature (mode QP). The effect of the incident angle on this transition scenario for the lowaspectratio cylinders is minimal. As the aspect ratio is increased towards 2, two synchronous modes, modes and , become unstable; these modes have spatiotemporal symmetries similar to their circular cylinder wake counterparts, modes A and mode B, respectively. While mode persists for all incident angles investigated here, mode is found only to be unstable for incident angles up to . Surprisingly, for , the mode A instability observed at zero incident angle emerges as a quasiperiodic mode as the incident angle is increased even slightly. At higher incident angles, this quasiperiodic mode once again transforms to a real mode on increasing the Reynolds number. The parameter space maps for the various aspect ratios are presented in the Reynolds numberincident angle plane, and the threedimensional modes are discussed in terms of similarities to and differences from existing modes. A key aim of the work is to map the different modes and various transition sequences as a simple body geometry is systematically changed and as the flow symmetry is systematically broken; thus, insight is provided on the overall path towards fully turbulent flow.
Original language  English 

Pages (fromto)  245283 
Number of pages  39 
Journal  Journal of Fluid Mechanics 
Volume  825 
DOIs  
Publication status  Published  25 Aug 2017 
Keywords
 parametric instability
 vortex shedding
 wakes
Equipment

eResearch Centre
Paul Bonnington (Manager)
Office of the ViceProvost (Research and Research Infrastructure)Facility/equipment: Facility