Two‐phase flow simulation of supersaturated total dissolved gas in the plunge pool of a high dam

Abstract

Total dissolved gas (TDG) supersaturation can cause potentially fatal Gas Bubble Disease (GBD) in fish and is recognized for its severe environmental impact for high‐dam operation conditions. The generation of supersaturated TDG in high‐head hydropower project is substantially different from middle‐ or low‐head projects that have been previously studied. Although the mechanics of TDG generation in a plunge pool are clearly three‐dimensional (3D), there are great challenges and difficulties of the 3D simulation for high‐dam projects. Toward this end, a two‐dimensional (2D) model of two‐phase flow in high‐dam plunge pool is developed with established computational fluid dynamics (CFD) software. New simulation modules are developed to account for a normal distribution of bubble sizes, which allows the TDG mass transfer from bubbles and across the free surface to include bubble size nonlinearities that were previously neglected. The model is calibrated based on observations from a high‐dam hydropower project with a ski‐jump spillway and deep plunge pool. Characteristics of simulated hydrodynamics, air‐bubble distribution, and TDG distribution downstream of the high dam were analyzed. Results showed that the model achieved satisfactory calibrated simulation of dissolved gas behavior and the assumption of a bubble normal distribution could properly reflect the bubble transfer process. Residence time in the plunge pool appeared to be a key factor determining maximum modeled TDG supersaturation levels. © 2016 American Institute of Chemical Engineers Environ Prog, 35: 1139–1148, 2016

Generation and Release Mechanism and Abatement Measures for Gas Supersaturation Downstream of Hydropower Dams: A Review

“…In addition, Ma et al. (2016b) used the established computational fluid dynamics software to develop a 2D model of two‐phase flow in the plunge pool downstream of a high dam and developed a new simulation module to explain the normal distribution of bubble size. However, a 2D simulation may not always accurately depict the actual flow conditions due to the intricacy of the dam's downstream flow.…”

Interaction of total dissolved gas supersaturation and suspended sediment on swimming performance of bighead carp (Hypopthalmichthys nobilis)

“…Total dissolved gas (TDG) supersaturation occurs downstream of high dams, especially when discharging abnormally high amounts of water (Qu et al, 2011). Previous studies found that various fish species suffered from gas bubble disease (GBD) due to TDG supersaturation (Qian et al, 2016). Under the influence of GBD, the blood vessels can be clogged with gas bubbles or emboli, resulting in the death of fish (Bouck, 1980).…”

Energy dissipation efficiency as a new variable in the empirical correlation of total dissolved gas

“…However, owing to insufficient knowledge of these processes, certain parameters may be neglected in the TDG prediction, leading to an increase in the error of the TDG prediction and restriction of the application range of the model 10 – 18 . Moreover, considerable calculations must be performed when implementing numerical models, and limited understanding of the two-phase flow movement, bubble transfer process and bubble density distribution may reduce the generality of such models 19 – 23 . Recently, alternative methods such as neural networks and high-order response surface methods have been used to model the generation of TDG by spilling 24 , 25 .…”