CFD Modeling of Air Pocket Transport in Conjunction with Spillway Conduits
2011 (English)In: 11th International Conferenceon Fluid Control, Measutements and Visualization, Keeling, Taiwan, December 2-9 2011, 2011Conference paper (Refereed)
This paper focuses on simulations of enclosed air pocket movements in conjunction with bottom outlet operations. The critical velocity of water for air pocket transport in pipe is the minimal flow velocity for the air pocket start to move downstream. A numerical model is developed to simulate the critical velocity of air pocket transport in pipe flow and to discuss the impacts of tunnel slope, size of the air pocket and wall roughness. The computations are performed in FLUENT using Volume of Fraction (VOF) model combined with k-epsilon model. Parallel computing is adopted for high computational performance.
The modeled critical velocity is compared with experimental results and they increase with increasing slopes. However, as the roughness height defined in the model is not big enough to represent the reality and no wall shear stress is applied in the upper wall where air pocket and wall contact, the modeled critical velocity is smaller than the experimental ones. Therefore, wall roughness contributes to keep the air pocket from moving downstream which is important in modeling critical velocity. However, by assuming a constant wall shear stress for the air phase the same as the water phase will overestimate the shear stress on the air pocket.
Two air pocket volumes are simulated at the slope 0.8 degrees which shows the bigger the air pocket is the higher the critical velocity is. Modeling results also show that the critical velocity is non-zero in horizontal pipe and there is a limit for the carrying capacity at all slopes. The simulations of air pockets with different volumes in the bottom tunnel of Letten dam in North of Sweden is shown in this paper as well.
Place, publisher, year, edition, pages
IdentifiersURN: urn:nbn:se:kth:diva-52306OAI: oai:DiVA.org:kth-52306DiVA: diva2:465886
QC 201112152011-12-152011-12-152012-01-10Bibliographically approved