Three Dimensional Hydrodynamics of Arced Piano Key Spillways

In this paper 3D free surface flow over the arced Piano Key spillway (APK) was numerically simulated and its hydraulic performance curves determined for various geometrical and hydraulic conditions. Three dimensional flow pattern around various types of APK were also determined and the differences between their performance with rectangular and trapezoidal piano key spillways discussed. The arced Piano Key spillways necessarily have trapezoidal keys and they should have advantages of trapezoidal weirs due to the increased inlet key area. Furthermore، the arced plan، bulged into the reservoir، eliminates the approaching flow channel mode and flow approaches perpendicularly to the spillway crest، from all directions. These phenomena lead to substantially increase of the discharge coefficient of the Piano Key spillways. By increasing the arced spillway angle، the discharge capacity increases. This is mainly due to the decrease of the local submergence over the outlet keys and increase of the inlet key area and modification of the overflow pattern.