A Time-Series Analysis of the Free-Surface Motion of Rotational Flow

抄録

We study the free-surface dynamics of rotational flow by time series analysis. In a flow driven by a rotating disk in a cylinder, the free surface irregularly switches between an axisymmetric shape and a nonaxisymmetric shape. This surface switching occurs in combination with significant elevation and elongation of the central part whose height has a strong correlation with the turbulent intensity. Although the number of degrees of freedom for the entire system is considerably large, the surface-shape dynamics indicates that the dimension needed to describe the major motion is much smaller compared with the whole system and the remaining part constitutes noise added to the major part. We have evaluated this conjecture by applying a diagnostic method and have clarified that the time series of the surface height is different from the white noise and the surrogate data of the original time series, both of which have no determinism.