水制の水理機能に関する研究(1) ―不透過水制の抵抗特性について―

Abstract

In this paper, the characteristics of the surface resistance of groynes of non-through type, which are placed in an open channel flow, are investigated experimentally by the relation betweenthe groyne clearance and the flow depth, because the description by usual methods such as a resso-tance coefficient, an empirical coefficient and an equivalent sand roughness can not always be applied.The results obtained through experiments are as follows; In the case of the flow depth exceedsthe groyne height, the normalized clearance-depth curve is characterized by two kinds of peaks offlow depth, one of which may be resulted from the effect of the vortex shedding and the other theshear stress at the surface of the separation region around groynes. Furthermore, the normalizedclearance-depth curve is affected by the groyne length and the height, but the effect of a change ingroyne width and phase difference between groynes placed along both sides of levees may be negli-gible. An increase of a Reynolds number brings an increase of the normalized groyne clearancecorresponding with the peak of flow depth resulted from the effect of shear stress, and brings adecrease of the normalized flow depth.On the other hand, in the case of the groyne height exceeds the flow depth, the meanderingeffect has a predominant role except for a comparablly small groyne length, which is examinedusing a flow visualization technique. The normalized clearance-depth curve is considerably affectedby the phase difference, in contrasted with the case of an exceeding flow depth, and the groyneclearances corresponding with two kinds of peaks of flow depth depend mainly on the channel width.