Hydropower and dam structures worldwide are facing evolving requirements due to changes in climate, better methods for flood estimates, combined with the needs of surrounding interests. Improved understanding of the hydraulic behavior of spillways, and the approach flow leading up to them, is important for evaluation of existing spillways and considering potential redesigns. There is limited research on the distribution of flow across a multiple outlet spillway, therefore a purpose built experimental setup is utilized to examine the impact of various geometrical changes on the flow distribution across a spillway with three outlets. The maximum difference measured between the different outlets were as much as 10%. While small changes to abutment and pier corners were found to reduce total discharge capacity up to 8%, with increased discharge and overflow height causing greater reduction in the capacity of the spillway. To further investigate the flow behavior leading up to the spillway outlets, ADV measurements were conducted to capture flow velocities. The measured flow cross sections indicate a stable flow field leading away from the inlet, stagnation zones and recirculation zones leading up to the spillway, with minor variations occurring for increasing inlet flow rates.

Measurements of mass flow through a three-outlet spillway modeled after a scaled-down spillway were conducted. The inlet and channel leading up to the outlets were placed to lead the water toward the outlet at an angle. With this, measurements of the water level at three locations were recorded by magnetostrictive sensors. The volumetric flow rates for each individual outlet were recorded separately to study the differences between them. Additionally, Acoustic Doppler Velocimetry was used to measure water velocities close to the outlets. The conditions changed were the inlet volume flow rate and the flow distribution was measured at 90, 100, 110, and 200 L per second. Differences between the outlets were mostly within the error margin of the instruments used in the experiments with larger differences shown for the 200 L test. The results produced together with a CAD model of the setup can be used for verification of CFD methods. A simulation with the k-epsilon turbulence model is included and compared to earlier experiments and the new experimental results. Larger differences are seen in the new experiments. Differing inlet conditions are assumed as the principal cause for the differences seen.

Experiments and computational simulations have been performed as part of a larger project to instil trust in computational methods for design of hydraulics flows in spillways. Presented in this licenciate is one manuscript and two conference papers. The first conference paper details experiments done at Älvkarleby of a multiple outlet spillway model with an inlet channel specifically designed to contain interesting hydraulic features. The results indicate that simulations agree well with experiments. In the second conference paper acoustic doppler velocimetry measurements (ADV) were done and compared to simulations of a racetrack flume with a fish passageway at Älvkarleby. The results showed agreement but due to inlet conditions of the experiment some discrepancies were noticed. The manuscript presents experiments of a wider range of flow in the experimental flume of the first conference paper, with additional ADV measurements. Preliminary conclusions are that discrepancies can be due to inlet conditions. A short summary of further work is included.

This paper presents the results from a physical model study of a fixed crest ogee spillway with lateral inflow creating a contraction loss at the inlet reducing the effective spillway width. The model represents a scenario faced by some spillway structures in low head run-of-river hydropower schemes. The contraction caused at the corner of the spillway inlet is quantified for varying discharges and its influence on the spillway capacity is evaluated. To improve the capacity of the spillway, firstly the approach angle is altered. The spillway capacity is measured for multiple headwall angles, finding a relative increase of 6.2 % in discharge capacity for a 55° approach. Secondly, guide walls of varying designs in the direction of the lateral flow are introduced. The design of the modified guide wall seeks to smoothen the approach and reduces the ensuing flow separation, thus increasing the capacity of the spillway. The greatest improvement is found for an elliptic guide wall which increased the discharge capacity by 6.7 %. Ultimately, small structural changes can make significant improvements to spillway capacity.

Mathematical modelling of single spillways is well documented in literature. For parallel spillways however, there is a lack of documented, verified, and validated cases. Here, in this article, ANSYS-CFX is used to simulate the flow over three parallel ogee-crested spillways. For mesh size verification, a grid convergence study is performed by Richardson extrapolation. The turbulence model chosen for this simulation is the k-ε model and the volume of fluid method is used to simulate the water-air interface. This article details the models ability to accurately predict flow distribution at the spillways, and the water levels. The mesh is kept relatively coarse at the channel inlet with increased mesh density at the spillways. The results are validated against experimental data from Vattenfall AB, R&Ds laboratories. The geometry and boundary conditions of the experiment are tailored for CFD. The flow rate of each spillway is measured separately with high accuracy, and for several different inlet volumetric flows. The simulation results lie within the error estimates of the measuring tools used in the experiments, within ±1%. The volume flow rate differences between the three outlets is very small, within ±1%.