河川の乱流構造に関する一考察

Abstract

It is spectrally distinct that the structure of large-eddy motion in a river flow isdescribed by a definite structure. The structure of the large-eddy presented by theauthors is "∩-shaped vortex tube" identical with the horseshoe vortex introduced byTheodorsen. The river flow may be considered in three parts, a mean flow, a set of the∩-shaped vortex tube and an ordinary turbulent motion made up of a wide and continu-ous range of eddy sizes. The ∩-shaped vortex tube slanting in a downstream directionand producing a jet-like motion away from a rive bed, gives a negative contribution tothe Reynolds stress and derives an energy directly from the mean flow to pass it on tothe smaller eddies. The smaller eddies may be defined as a multiple arrangement ofsmaller vortex filaments which cover the surface of the ∩-shaped vortex tube. Formationof a so-called "boil" at the surface of river is well interpreted by the existence of the∩-shaped vortex tube.