Numerical investigation of flow behavior over arced trapezoidal piano key weirs

Weir is one of the most common artificial hydraulic structures that are used to measure flow in canals, divert flow, store water, change the flow regime in canals and control floods during rainfall. Free weirs are divided into two categories: linear and non-linear. One of the most important advantages of piano key weirs compared to linear weirs is the improvement of flow transfer capacity by increasing the length of the crest and as a result, increasing the length of the water passage in a fixed width of the construction without increasing the upstream water load.The purpose of this research is to numerically model the flow and investigate the effect of simultaneous changes in the number of cycles and the angle of the weir on the flow coefficient by trying to keep the total length of the weir crest and other geometric parameters constant for all models. After the investigations, it was found that increasing the weir angle of the piano key at a fixed length for all models increases the flow coefficient, while increasing the number of cycles at a fixed length for all models due to the reduction of the inlet key water tank area, increasing the contraction of the current stream lines and then intensifying the local submergence in the outlet key, the current permeability coefficient will decrease significantly