Supercritical flow in bend manhole

Supercritical flow in a bend manhole for combined sewer systems is consider ed for a typical relative curvature and deflection angles of 45 degrees and 90 degrees. The typical features of bend flow in a U-shaped channel are de termined, including the surface profiles along the inner and the outer bend walls, impact flow at the manhole outlet into the downstream sewer pipe, a ir entrainment characteristics, and wave development in the downstream sewe r. Also, typical velocity distributions along the manhole are presented, an d the capacity of the conventional bend structure is determined. To increas e the discharge capacity across a bend manhole, the so-called bend cover is introduced. This cover element finished in steer can be removed for mainte nance and inspection purposes. It limits the wave height close to the bend outlet to 90% of the sewer diameter and allows air entrainment into the dow nstream sewer. The performance and capacity of bend flow may significantly be increased, and the novel element may easily be added to existing manhole s.