Determination of effective flow behaviors on discharge performance of trapezoidal labyrinth weirs using numerical and physical models

Labyrinth weirs are often preferred to linear weirs in practice because they offer a higher discharge capacity for the same headwater. However, with increasing relative crest length, the discharge performance approaches that of linear weirs due to nappe interference and local submergence downstream of the labyrinth weirs, particularly at high heads. It is important to analyze the hydrodynamics of the weir flow in detail to better understand this paradox in the performance of labyrinth weirs, which have a complex flow pattern. Therefore, in this study, a three-dimensional numerical model study was carried out together with the physical model to reveal the hydrodynamic behavior on the discharge performance of trapezoidal labyrinth weirs under free overflow condition. Physical model measurements were used to validate and calibrate the numerical models. The numerical model results show that the flow conditions in the downstream cycles (i.e. nappe interference, submergence) as well as the flow characteristics in the upstream cycles (i.e. effective lateral flows) have significant effects on the hydraulic efficiency of the labyrinth weirs. The study also presents two new highly correlated equations obtained by multiple regression to calculate the discharge coefficients of the sharp-crested trapezoidal labyrinth weirs. The results were compared with some studies in the literature and thus the model performances were discussed.