Basic Characteristics of Autorotating Flat Plate in Flow

摘要

In the present study, the authors conduct subsonic wind-tunnel experiments, in order to investigate the effect of a depth-to-width ratio 2 upon the tumbling of a simple two-dimensional rectangular-cross-section prism. The authors carry out both flow visualisation and velocity measurement using a hot-wire anemometer, together with the synchronised measurement of a prism's attack angle a, which are analised using a phase-averaging technique. As a result, there are two modes for λ < 0.6 and λ≥ 0.6. For λ< 0.6, large-scale two vortices are emitted during one prism's rotation, although the dominant velocity fluctuation has the period corresponding to one prism's rotation, namely, is in 360 cycle of a. For λ ≥0.6, large-scale four vortices are emitted during one prism's rotation, although the dominant velocity fluctuation has the period corresponding to a half prism's rotation, namely, is in 180° cycle of a. Especially, for λ = 0.5, we can see transition-process features between the two modes. For λ < 0.6, momentum deficit AC increases with increasing λ. For λ > 0.6,M_d decreases with increasing λ. Then, we can see the maximum value of M_d for λ= 0.6.