Three dimensional numerical modelling of free surface flows over hydraulic structures

With increasing water demand and higher occurrence of extreme flooding events, the design and upgrade of hydraulic infrastructure like weirs and spillways is critical for human safety and development. The current industry practice of hydraulic modelling for the design of this type of hydraulic structures is physical scale hydraulic modelling. Because hydraulic models are not capable of satisfying the ratios of all forces between prototype and model simultaneously, scale effects inevitable. Advances in computer processing power allowed the development of numerous numerical approaches to model free surface flows. The information provided by Computational Fluid Dynamics (CFD) models provides richer understanding of the problem as well as the ability to simulate the full scale prototype flow conditions. 3D CFD models have a strong potential to provide accurate and flexible solutions with high prospects of time and cost savings in the design process. However, these models have been validated only in a limited number of cases and flow conditions to model free surface flows over full scale complex hydraulic structures like weirs and spillways. Further evidence of accurate numerical modelling this type of problems is needed to demonstrate the reliability of such numerical approaches for specific applications. One of the most well-known CFD models to simulate hydraulic free surface flows is the Eulerian grid-based Volume of Fluid (VOF) model. In the present work the capabilities of the VOF method to reproduce a real hydraulic structure are evaluated and utilised to provide insight into scale effects. In order to validate the numerical model, the physical model of a hydraulic structure is first simulated. Subsequently, modelling of the full scale prototype is undertaken. Results to-date show the full scale flows are expected to be faster and shallower than those predicted by the physical scale model. In addition, the scaled and the full scale wave configurations present substantial differences in length and shape. Therefore this study highlights the merits of performing CFD simulations for the design of hydraulic infrastructure.