STABILITY OF FLOW PAST TWO SIDE-BY-SIDE CIRCULAR CYLINDERS

The global stability of flow past two side-by-side circular cylinders is investigated by a linear global stability analysis method based on a spectral/element Navier-Stokes solver. The special attention is paid to the parameter regime of 1 < T/D < 3, where T is the spacing between two cylinder centers and D the cylinder diameter. A remarkable feature we found is that there exist two critical Reynolds numbers associated with twice bifurcations, first a pitchfork and second a Hopf one, for about 1.55 < T/D < 1.65. A new flow pattern namely biased steady pattern is identified. In addition, the transition from in-phase lock-in to anti-phase lock-in pattern for larger separation distance T/D > 1.65 is proved to be related to the switch between two leading eigenmodes.