Decay of Turbulence in a Closed Vessel : (2nd Report, Time-Scales of Turbulence)

This paper presents an experimental study concerning the variation of the microscopic characteristics of a decaying turbulence generated in a closed vessel. The decaying process was analyzed on the assumption that the turbulence was able to be treated as steady during a short time interval along the decaying curve. That is to say, for such time interval, the relation between the fluctuating components as well as their time scales and the mean flow components was investigated. The time scales (mean-time-scale, micro-time-scale and energy-mean-frequency) were derived from the Eulerian correlation function and the spectrum function of the measured fluctuating velocities. The results are : (a) the difference between characteristic of turbulence in the pre-relaxation stage and the one in the relaxed stage (defined in the first report) was made clearer, and (b) the behavior of variation in characteristic values (fluctuating components and time scales of turbulence) was made known.