平面クエット流の乱流縞における生成・崩壊サイクルの実験観測

抄録

In this study, visualization experiments of plane Couette flow were conducted to investigate the spatio-temporal variation of turbulent stripes, the spanwise wavelength, and the process of their generation and breakdown. The experiments were performed with three different film half-widths (δ = 2.90 mm, 3.39 mm, and 4.30 mm). Two cycles of generation and breakdown of turbulent stripe were successfully captured. We defined long-life and short-life cycles based on the order in their appearance, respectively. For each film half-width, the survival time of turbulent stripes, that appeared in the long-life cycle, was t* = 1620, 1960, and 556, respectively, and the number of turbulent stripes was confirmed as 2, 1, and 1. The elapsed time t* since the observation started was non-dimensionalized by the film velocity and half-width. Similarly, the survival time of turbulent stripes, that appeared in short-life cycle, was t* = 970, 1240, and 0, respectively, and the number of bands was 5, 1, and 0. In the case of a film half-width of 2.90 mm, five turbulent stripes were visualized, the largest number in this study. Based on the results, it was found that the number of turbulent stripes decreases and the spanwise wavelength increases as the film half-width increases. This tendency is not considered to be organized on an outer scale, given the standard deviations of the film half-widths. Considering the distribution ratio of the pressure-strain correlation term or friction velocity in turbulent stripes of numerical simulations in previous studies, the tendency for differences in the number of turbulent stripes and spanwise wavelengths at each film half-width to be organized on a viscous scale is considered reasonable.