CFD-modeling of labyrinth weir flood discharge with ice cover

Sammanfattning: A labyrinth weir is a hydraulic structure built with a purpose to increase the discharge capacity compared to linear weirs, while maintaining the same water level upstream. Construction of labyrinth weirs is vital in a future with more unpredictable flows. Labyrinth weirs in cold weather climates will result in ice formation during winter, in some cases the ice will form a cover above the water surface level. This ice cover can form upstream of the weir, or form in between the weir walls, obstructing the flow and act as a raised channel bed.A rectangular labyrinth weir was created from dimensions of a reference project, and a computational domain and mesh was created to analyse flow patterns at the weir, both with and without the ice cover. Four different cases were evaluated: no ice cover (NI), partial ice cover (PI), upstream ice cover (UI) and whole ice cover (WI). These cases were tested for five different upstream heads above the weir crest, to evaluate the differences between small flows and large flows. Water surface level, unit discharge, volume fraction with velocity vectors and velocity plots with direction vectors were allused to analyse differences between the different cases of ice to determine its impact on the flow.The ice cover has the greatest impact on the flow when it forms between the walls of the labyrinth weir. For smaller flows, discharge is reduced with 50%, and flow pattern is drastically changed. When ice forms only upstream of the weir, the impact is minor as deep flows still discharge through the inlets of the weir. In conclusion, ice cover formation needs to be a factor for designing labyrinth weirs in cold weather climates, as it will alter the function of the weir.