Shahrood University of TechnologyJournal of Hydraulic and Water Engineering2980-986X1220240101Numerical Simulation of Flow Over the Arced Trapezoidal Piano Key Weir105136300110.22044/jhwe.2023.13037.1013ENAdel EdalatiPh.D. Student of Water and Hydraulic Structure, Civil Engineering Collage, Shahrood University of Technology, Shahrood, Iran.Ramin AminiAssociate Professor, Department of Water and Environmental Engineering, Civil Engineering Collage, Shahrood University of Technology, Shahrood, Iran.Journal Article20230430Weir is one of the most common man-made hydraulic structures that are used to measure the flow in canals, store water, and control floods. The piano key weir (PKW) is a type of non-linear weir and is considered one of the best hydraulic-economical options for use in improvement projects to increase the discharge capacity during floods and increase the reservoir volume (with increasing the length of the water passage in a fixed width of the construction) in new dam construction projects. 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 weir angle on the discharge coefficient by trying to keep the total length of weir crest and other geometric parameters constant for all models. After the investigations, it was found that increasing the weir angle of the PKWs in a fixed length, for all models, increases the flow coefficient while increasing the number of cycles in a fixed length, for all models, leads to the reason for the reduction of the area of the inlet keys, increased contraction of streamlines and the subsequent intensification of the local submergence in the outlet keys, the discharge coefficient will decrease significantly. In the end to predict the changes of the discharge coefficient variable, the conditions of using the multiple regression model, two groups of dimensionless parameters depending on the geometry and flow through the weir were examined and new relationships were presented to calculate the discharge coefficient.https://jhwe.shahroodut.ac.ir/article_3001_84f05ff87c82736ee40565f4ddaf48df.pdf