Free surface aeration and development dependence in chute flows

Abstract

The microscopic description of the mixture behaviour of air–water flow remains a challenge. It is not clear how to represent a complex two-phase interaction with the turbulent air–water structure development process. In this study, based on the air–water mixing fluctuation properties in self-aerated chute flows, a prediction model of air concentration distribution related to a theoretical transition depth is developed. The air–water turbulent mixing analysis reveals that the mixture flow depth, at which the local air concentration is 0.5, represents the interior transition boundary. The agreement of the calculated results with the test data confirms that local water and air turbulent mixing through the free surface area should be equally considered. On the basis of the interior transition depth, the development of self-aeration mainly manifests as the air turbulent mixing process in the low aerated region, while the water turbulent mixing in the high aerated region remains mostly unchanged. A series of relationships concerning the development of self-aerated flows is proposed to enable quantitative estimations in practical applications of water engineering.

Linking turbulent waves and bubble diffusion in self-aerated open-channel flows: two-state air concentration

“…The transition point between the two regions, defined by the depth with corresponding air concentration , was determined based on the maximum gradient by Straub & Anderson (1958). In contrast, Wei & Deng (2022) argued that the flow depth , i.e. the depth where , can be used as interior transition depth, and Wei et al.…”

Turbulent free-surface in self-aerated flows: superposition of entrapped and entrained air

“…Figure 6( a ) compares equilibrium air concentrations from Straub & Anderson (1958) with the present reanalysis, showing that Killen's (1968) measurements were taken in the GVF region. Following Wei & Deng (2022), Killen's (1968) mean air concentrations are normalised with their equilibrium value, approximated as (Hager 1991), and plotted against the dimensionless streamwise coordinate (figure 6 b , c ). This normalisation shows a good collapse of the four different measurement series, thereby demonstrating how the two-state superposition model can be used to finely differentiate between different physical processes in the streamwise decomposition of .…”

“…As such, the characterisation and the modelling of air concentration distributions has been subject to sustained research interest over the last decades. Different groups of researchers have conceptualised the air concentration using single-layer (Rao & Gangadharaiah 1971; Wood 1991; Chanson & Toombes 2001; Valero & Bung 2016; Zhang & Chanson 2017) or double-layer approaches (Straub & Anderson 1958; Killen 1968; Wei & Deng 2022; Wei et al. 2022).…”

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

“…The gas concentration when the gas dissolution in water reaches the phase equilibrium state is called the equilibrium concentration, and when the dissolved gas concentration in water is higher than the equilibrium concentration, the TDG supersaturation will occur (Du, 2017). The process of generation and release for TDG supersaturation can be summarized in three stages: (a) aeration stage (Colt & Westers, 1982; Wei & Deng, 2022), (b) generation stage (P. C. Li et al., 2022; Zhang et al., 2020), and (c) release stage (Kamal et al., 2019; Lin et al., 2021) as shown in Figure 2.…”