Aeration and air–water mass transfer on stepped chutes with embankment dam slopes

Abstract

Stepped spillway flows are characterised by significant free-surface aeration downstream of the inception point of air entrainment. The stepped design is advantageous for applications which require large energy dissipation and strong flow aeration. While the energy dissipation rate for embankment stepped spillways was studied previously, the optimum design for aeration and air-water mass transfer is not known. Herein new air-water flow experiments were conducted on several stepped spillways with embankment dam slopes using with phasedetection intrusive probes. The present data were compared with previous studies in terms of energy dissipation, flow aeration and air-water mass transfer. The air-water mass transfer was calculated based upon air-water flow measurements in terms of dissolved oxygen. The re-oxygenation rates were compared with previous studies comprising both conductivity and direct dissolved oxygen measurements. The comparison highlighted a monotonic increase of aeration efficiency with energy dissipation rate. All data were in good agreement independent of channel slopes, stepped configuration and sensor size. The data confirmed the effects of strong air-water interactions within the bulk of the flow for both energy dissipation and re-oxygenation performances.

Flow Resistance and Energy Dissipation in Supercritical Air‐Water Flows Down Vegetated Chutes

“…The range of C mean for the vegetated chutes (0.14 ≤ C mean ≤ 0.41 with an average value of C mean ≈ 0.25) compared well with observations of aerated flows on rock chutes of 0.20 ≤ C mean ≤ 0.37 for 14.8° ≤ θ ≤ 20.8° (Pagliara et al, ) and stepped chutes of 0.15 ≤ C mean ≤ 0.46 for 3.4° ≤ θ ≤ 26.6° (Felder & Chanson, ). The close agreement with previous studies on fully aerated spillway flows confirmed the significance of flow aeration in supercritical flows down vegetated slopes.…”

Air–Water Properties in Rectangular Free-Falling Jets

“…Near the weir crest (L/h < 15-20), the relationship between the bubble frequency and the void fraction seemed to have a good fit with the parabolic behavior reported by Toombes [35] and Brattberg et al [36] in other kinds of air-water flows. The maximum values of F/F max were obtained around C = 0.40 and 0.60 in the majority of the crosssections analyzed.…”

Converging stepped spillway flow

“…Intense turbulence, which occurs in supercritical flows, causes strong interactions between the water and the atmosphere that results in air entrainment (Pfister & Hager, 2011;Takahashi & Ohtsu, 2012). Similar to Chanson and Toombes (2004), Felder and Chanson (2015) and Toombes (2002), the flow-field measurement in the air-water mixture was conducted using a multi-tip conductivity (EC) probe. The EC probe used in this research was similar to the one used by González (2005) and Toombes (2002) with the tip diameter of 0.3 mm and had two side probes instead of one.…”