Labyrinth Weirs with Angled Approach Flow

Current design methods and research have primarily investigated the hydraulic characteristics of labyrinth weirs when the approach flow is perpendicular to the weir axis, a condition consistent with most in-channel and in-reservoir applications where the approach velocity is negligible. In some cases, a perpendicular approach flow and weir axis alignment may not be possible. The head-discharge characteristics of a four-cycle, 15 degrees labyrinth weir with a channelized approach flow were evaluated with three different approach flow angles (0 degrees, 15 degrees, and 45 degrees) using laboratory-scale physical models. Although the data presented are specific to the geometry of the weir and channels tested, they provide a general indication of variations in discharge efficiency as a function of approach flow angle. The experimental data were also compared with the head-discharge characteristics of a prototype labyrinth weir model study that featured significant approach flow angles. For approach flow angles under 15 degrees, no measurable loss in discharge efficiency occurred, relative to an approach flow angle of 0 degrees. The discharge efficiency reduced by as much as 11% for the 45 degrees approach flow angle case. Flow instability was observed downstream of the weir, producing unique flow patterns in the labyrinth cycles and on the spillway apron. (C) 2018 American Society of Civil Engineers.