Bend losses in drop inlet spillways

Abstract

The drop inlet spillway consists of a vertical riser open at the top and connected to a horizontal conduit or tunnel at the bottom. A 90° change in direction is required at the connection between the riser and the conduit. In the interests of simplicity a square bend, sometimes called a miter bend, is often used for small unimportant structures. This type of bend produces separation zones and large eddy losses (bend loss). At the other extreme is the fully curved bend, commonly used for large shaft spillways. A properly designed curved bend will eliminate separation and minimize head loss. However, layout and forming for construction of a curved bend for a tunnel is complicated and expensive because the elbow surface is of double curvature.In this paper the results of hydraulic tests on five bend designs are presented. It was found that a simplified design with only an inside curve performed almost as well as the fully curved bend. It is suggested that the proposed design will meet the requirement for many low head drop inlets where use of the fully curved bend is not warranted but the square bend is not satisfactory.