A physical experimental setup of a circular, gated closed conduit was built at the Utah Water Research Laboratory (UWRL). Setup configurations were modified and data were measured to aid in the study of physical variables on air demand. It was determined that gate opening, gate and water surface roughness, and conduit length all were significant variables on the air demand measured through the conduit air vent. It was also determined that no noticeable air velocity profile existed above the air-water interface. A linear relationship was found between the air flow rate to water flow rate ratio (air-demand ratio) and head-to-gate height ratio when identical conduit geometry was used. Data obtained from this study illustrated that the use of the Froude number is an incomplete way to quantify air demand due to the effects of changing conduit geometry.

Aeration issued through a ventilation shaft is an important measure to prevent cavitation and large gauge pressure in flood discharge tunnels. In order to dimension the ventilation shaft appropriately, itis necessary to have a good understanding of the air-water flow in the tunnel. In this study, the multiphase flow through a discharge tunnel was simulated in the computational fluid dynamics (CFD) software ANSYS Fluent. Since the flow was separated, the simulation setup used the volume of fluid (VOF) multiphase model, that could track the water surface. Furthermore, the so called RNG k-epsilon turbulence model was used. The CFD model was validated with measured data provided from two open channel experiments carried out on a scaled model at Sichuan University. To ensure mesh independence, grid convergence index (GCI)studies were performed for the two validating cases. After the validation, a top wall and a ventilation shaft was added to the CFD model. The flow was then simulated for four different shaft designs and four different water inlet velocities. The air demand and air supply for the various scenarios could thereby be calculated. The results of this study were also compared with previous research on multiphase flow through tunnels with similar design. It was concluded that the air flow downstream in the tunnel converged for the two larger designs. It was also concluded that the air demand in the tunnel was satisfied for the larger ventilation shafts. A smaller study on cavitation was made and the risk was considered non-existent for all the simulated cases.