Experiments and CFD modeling of high-velocity two-phase flows in a large chute aerator facility

• Main Authors: James Yang, Penghua Teng, Hongwei Zhang
• Format: Article
• Language: English
• Published: Taylor & Francis Group 2019-01-01
• Series: Engineering Applications of Computational Fluid Mechanics
• Subjects: aerator; two-phase flow; two-fluid model; drag force; wall lubrication force; air cavity
• Online Access: http://dx.doi.org/10.1080/19942060.2018.1552201
• ISSN: 1994-2060; 1997-003X

Mathematical formulations of two-phase flows at an aerator remain a challenging issue for spillway design. Due to their complexities in terms of water–air interactions subjected to high flow velocities, experiments play an essential role in evaluations of numerical models. The paper focuses on the underlying influence of the air–water momentum exchange in the two-phase Two-Fluid Model. It is modified to better represent the drag force acting on a group of air bubbles and the wall lubrication force accounting for near-wall phase interactions. Based on data from a large aerator rig with an approach velocity of 14.3 m/s, the models are evaluated for calculations of entrained air characteristics of a flow mixture. The air bubble diameter used in the modeling ranges from 0.5 to 4 mm as suggested by the experiments. In terms of air cavity configurations and aerator air demand, smaller air bubbles lead to better agreement with the test results. As far as air concentrations are concerned, the modified model gains by comparison. In the air cavity zone, smaller bubble sizes also provide better matches with the experiments. However, the near-base air concentration remains overestimated downstream from the impact area. The fact that the program user must pre-define a single air bubble size in simulations presumably limits the correct reproduction of near-base air concentrations and of their decay.