Adaptation of stilling basins to higher discharges than those considered for their design implies deep knowledge of the flow developed in these structures. To this end, the hydraulic jump occurring in a typified United States Bureau of Reclamation Type II (USBR II) stilling basin was analyzed using a numerical and experimental modeling approach. A reduced-scale physical model to conduct an experimental campaign was built and a numerical computational fluid dynamics (CFD) model was prepared to carry out the corresponding simulations. Both models were able to successfully reproduce the case study in terms of hydraulic jump shape, velocity profiles, and pressure distributions. The analysis revealed not only similarities to the flow in classical hydraulic jumps but also the influence of the energy dissipation devices existing in the stilling basin, all in good agreement with bibliographical information, despite some slight differences. Furthermore, the void fraction distribution was analyzed, showing satisfactory performance of the physical model, although the numerical approach presented some limitations to adequately represent the flow aeration mechanisms, which are discussed herein. Overall, the presented modeling approach can be considered as a useful tool to address the analysis of free surface flows occurring in stilling basins.

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The study of the hydraulic jump developed in stilling basins is complex to a high degree due to the intense velocity and pressure fluctuations and the significant air entrainment. It is this complexity, bound to the practical interest in stilling basins for energy dissipation purposes, which brings the importance of physical modeling into the spotlight. However, despite the importance of stilling basins in engineering, bibliographic studies have traditionally focused on the classical hydraulic jump. Therefore, the objective of this research was to study the characteristics of the hydraulic jump in a typified USBR II stilling basin, through a physical model. The free surface profile and the velocity distribution of the hydraulic jump developed within this structure were analyzed in the model. To this end, an experimental campaign was carried out, assessing the performance of both, innovative techniques such as the time-of-flight camera and traditional instrumentation like the Pitot tube. The results showed a satisfactory representation of the free surface profile and the velocity distribution, despite some discussed limitations. Furthermore, the instrumentation employed revealed the important influence of the energy dissipation devices on the flow properties. In particular, relevant differences were found for the hydraulic jump shape and the maximum velocity positions within the measured vertical profiles, when compared to classical hydraulic jumps.

A classical hydraulic jump of Fr1=6 and Re1= 210,000 was characterized using the Computational Flu id Dynamics (CFD) codes OpenFOAM and FLOW-3D, whose performance was assessed. The results were compared to experimental data from a physical model designed for the purpose. The most relevant hydraulic jump characteristics were investigated, including hydraulic jump efficiency, roller lengt h , free surface profile, distributions of velocity and pressure and fluctuating variables. The model outcome was also compared to previous results from the literature. It was found that both CFD cod es rep resent wit h high accuracy the hydraulic jump surface profile, roller length, efficiency and sequent depths ratio, consistently with previous research. Some significant differences were found between b ot h CFD co d es regarding velocity distributions and pressure fluctuations , although in general results are in good agreement with experimental and bibliographical observations. This makes models of these characteristics suitable for engineering applications involving design and optimization of energy dissipation devices.

The adaptation of existing dams is of paramount importance to face the challenge posed by climate change and new legal frameworks. Thus, it is crucial to optimise the design of stilling basins so that a reduction in the hydraulic jump dimensions is achieved without jeopardising the energy dissipation in the structure. A numerical model was developed to simulate a United States Bureau of Reclamation Type-II basin. The model was validated with a specifically-designed physical model and then was used to simulate and test the performance of the basin after adding a second chute blocks row. The results showed a reduction in the hydraulic jump dimensions in terms of the sequent depths ratio and the roller length, which were respectively 2.5% and 1.4% lower in the modified design. These results would allow an estimated increase of the discharge in the basin close to the 10%. Furthermore, this new design showed a higher efficiency, with a 1.2% increase in this parameter. Consequently, the modifications proposed for the basin design suggest an improved performance of the structure. The issue of the hydraulic jump length estimation is also discussed, introducing and comparing different approaches. These methods follow a structured and systematic procedure and show consistent results for the developed models.