Supercritical flow in 45°-junction manhole

ATV Project in collaboration with University of Naples

• Dr. G. Del Giudice,
• Prof. Dr. W.H. Hager

Junction manholes in sewer systems are not yet designed according to a standard, such that their geometries may be subject to local variations. The present project involved a so-called simple junction manhole with a straight-through branch to which a 45° lateral branch was connected, with the sewer diameters D identical for the upstream, the lateral and the downstream branches. The radius of curvature of the lateral branch was equal to 3D.

For supercritical upstream flow, various flow regimes may occur:

1. Supercritical flow in all three branches,
2. Lateral branch flow subcritical because of dominant upstream flow, and
3. both lateral and upstream branch flows subcritical because downstream branch limits flow.

A significant question thus relates to the governing flow pattern for a given manhole configuration (Fig.1). Hydraulic model observations were thus conducted to answer this question in addition to the internal flow characteristics of these complex free surface flows.