STUDIES ON FLOW WITH VERY MILD HYDRAULIC GRADIENT (1st Report) -EXPERIMENTAL STUDY ON DAMED-UP FLOW IN SMOOTH OPEN CHANNEL-

This paper describes the experimental results and the several discussions on thehydraulic behaviour of a dained-up flow in a smooth open channel, as 1st step of studieson the flow with very mild hydraulic gradient in a open channel.The experiments were carried out for the flow of 1.35-16.66 1/sec in discharge inthe steel chsnnel of 0.3 in width and 21 in length.It is disclosed as a result that the value of resistance coefficient defined by fre/pu, , , ', in which ~, is the shearing stress on boundary, p the density of water and Cmthe average velocity of flow, for such the flow shows the tendency to be larger thanthat for a uniform flow with same Reynolds number.This seems to be caused by the followings;I) the resistance coefficient Cj=ro/puo', in which u, is the maximum velocity in thecross-section, varies with the value of dh/dx, ii) there exists the condition restricting the growth of boundary layer, iii) the effect of side walls on the flow is considerable large, and so on.However, the analytical investigation on this problem remains in future.This paper describes the experimental results and the several discussions on thehydraulic behaviour of a dained-up flow in a smooth open channel, as 1st step of studieson the flow with very mild hydraulic gradient in a open channel.The experiments were carried out for the flow of 1.35-16.66 1/sec in discharge inthe steel chsnnel of 0.3 in width and 21 in length.It is disclosed as a result that the value of resistance coefficient defined by fre/pu,,,', in which ~, is the shearing stress on boundary, p the density of water and Cmthe average velocity of flow, for such the flow shows the tendency to be larger thanthat for a uniform flow with same Reynolds number.This seems to be caused by the followings;I) the resistance coefficient Cj=ro/puo', in which u, is the maximum velocity in thecross-section, varies with the value of dh/dx,ii) there exists the condition restricting the growth of boundary layer,iii) the effect of side walls on the flow is considerable large, and so on.However, the analytical investigation on this problem remains in future