河川におけるレイノルズ応力の分布について

Abstract

Observations have been made of u' and w', the longitudinal and vertical componentsof turbulent velocity, in the Uji river. The measuring instrument was an ultrasonic fiowmeterbased on the method of sing-around, and was possible to measure two components of velocitysimultaneously. The mean velocity u was about lm/sec, and the r. in. a. values of u' were ofthe order of 10% of u, while those of w' were about 6% of u. The shearing stress seemsto be increased approximately linearly from surface to bottom. Near the center of the depth, the values of the stress were about 60 dyn/cmt, the corresponding coefficient of correlationbetween u' and w' averaging -0.65. The values of the Reynolds stress were nearly equalto those of the variance of w'-fluctuation. The integral time scales of u' were about three timesas large as w'. Auto- and cross-spectral analyses computed from these records show thatthere exists a region satisfying the law of -5/3 power in the spectrum of u' and w' aspredicted by the Kolinogorov theory, while the cospectruin between u' and w' nearly satisfiesthe law of -7/3 power.