開水路における桟型人工粗度の実験的研究

Abstract

One of the most difficult works on the open-channel model experiments is toproduce the roughness required to fit the similitude. This paper presents someresults of an experimental investigation of artificial strip roughnesses for thepurpose of application to hydraulic open-channel models.The flow over surfaces with strip roughness may be divided into three typesin accordance with the strip spacing ; the first type of flow is perfect wake-inter-ference flow, the second type imperfect wake-interference flow and another typeisolated roughness flow. The equivalent sand grain roughness of Nikuradse isavailable for the frat type of flow. However, in the cases of the other types offlow it should be considered that the flow condition is not 4niform in the directionof flow, since a wake from one roughness element diffuses considerably before itreaches the next element. Based on this concept of flow, the datum level ofroughened surface is defined from the measurement of the drag force of the striproughness element, and the experimental constants contained in the logarithmicresistance law are determined for relative roughness spacings.