Numerical Simulation of Autorotation

概要

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Autorotation of an elliptic cylinder around its spanwise axis fixed perpendicularly in a uniform flow was numerically simulated by using discrete vortex-blob method and compared with experimental results using wind tunnel and water channel. The flow fields around the cylinder driven externally with constant angular velocity were investigated, and the effects of the moment of inertia and of the thickness ratio of the cylinder on the starting condition of autorotation were analyzed, which clarified the mechanism of autorotation. That is, the driving force is due to shedding of the vortex clinging behind the retreating edge. The cylinders with sufficiently large moments of inertia rotate with constant angular velocity, whereas those with smaller one induce periodic variation of angular velocity. The cylinders with smaller moment of inertia than a critical value cannot sustain autorotation. It was also found that the autorotation frequency increases as the thickness ratio of the elliptic cylinder decreases, and eventually reaches the maximum values which is larger than the one of a flat plate.
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