Stability of wakes behind elongated bluff bodies at incidence

Flow past elongated bluff bodies for Reynolds numbers Re ≼ 500 is investigated here for incident angles I ≼ 20°. Two-dimensional simulations are performed using a spectral element solver for elliptical shaped cylinders for aspect ratios AR ≼ 2.5 to first obtain the base flows, following which linear stability analysis is performed on the unsteady base flows to investigate the onset of three-dimensional modes. For low aspect ratio cylinders, the transition sequence from steady two-dimensional flow to unsteady three-dimensional flow (steady → unsteady → mode A → mode B → mode QP) closely resembles that of a circular cylinder for all incident angles. As the aspect ratio is increased, the onset of the these transitions is delayed to higher Reynolds numbers for a given incidence angle, while the onset of the three-dimensional modes occurs at lower Reynolds numbers on increasing the incidence angles. The behaviour of the various three-dimensional modes is investigated in this parameter space.