The dynamic nature of our world has led to an increase in the magnitude of flood estimates used in reservoir hydraulic design. As a result, many existing spillways are now undersized and unable to meet current flood discharge requirements. A viable solution to replace a linear weir, which is constrained by a fixed footprint, is to upgrade the weir with a nonlinear weir, such as a labyrinth weir. The plan view of arced labyrinth weirs can enhance hydraulic efficiency, in certain reservoirs, due to better orientation of individual cycles of the weir to the approaching flow from the reservoir.
The hydraulic characteristics of spillway control structures (e.g., weirs) should be verified using applicable published data or hydraulic modeling (physical and/or numerical) in the absence of published data specific to the spillway design of interest. The questions posed in this study are: Do computational fluid dynamics (CFD) model results differ among the various software packages, namely Flow-3D and StarCCM+? How do user-defined settings affect the results? And how do these results compare with experimental data from a scaled physical model? As a basis for comparing these two CFD alternatives, the hydraulic performance of an arced labyrinth weir was evaluated using each software package, relying on software provided default settings, along with variations in user-defined options (e.g., turbulence model, grid cell size, etc.). Five head-discharge data points resulting from the software were compared with experimental data.
Both numerical models accurately depicted the behavior of the water as it passes over the crest (nappe), when compared with the physical model. Flow-3D provided better user experience and the most accurate results. StarCCM+ provided more user-defined options and a steeper learning curve, while still producing accurate results. More refining could have been completed in StarCCM+ to potentially provide results that more closely matched the physical model. The results of the study indicate that default settings are not always suitable for developing a rating curve. CFD modeling can prove to be a valuable tool for implementing site-specific conditions for arced labyrinth weirs; however, it is important to calibrate CFD models using reliable laboratory or field data. The data from this study may be utilized, with sound engineering judgment, to assist in the design of arced labyrinth weirs.
