Instabilities in the flow behind rotating bluff bodies

Abstract eng:
The wake and its instabilities behind rotating sphere and a simplified model of propeller were investigated for moderate Reynolds numbers, in a low- velocity water channel. We observed different vortex structures with LIF method and the velocity field was measured with PIV. The influence of rotation speed on vortex shape and size was analysed. The explored range of Reynolds number was from 0 to 400 and the swirl or rotation parameter Q was not higher than 4 for the sphere and 2 for the rotor. For non-rotating bodies, is very well know the existence of various flow regimes with axisymmetric base flow, pairs of stationary counter-rotating vortices, and unsteady vortex shedding with hairpins. We described the occurrence of new regimes in presence of rotation with lower and higher helical modes. In this talk new results about the non- linear evolution of the instability modes are presented.

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