Free-surface and Seepage Bubbly Flow on a Gabion Stepped Spillway Weir: Experimental Observations

Hubert Chanson, Gangfu Zhang

Thursday 2 july 2015

15:05 - 15:20h at Africa (level 0)

Themes: (T) Special session, (ST) Acoustic monitoring of flow, turbulence and river discharge

Parallel session: 12F. Special session: Acoustic monitoring of flow, turbulence and river discharge

On a gabion stepped weir, the steps contribute to some dissipation of the turbulent kinetic energy, while some seepage takes place in the gabions. Herein a new experimental investigation was conducted in a large size stepped weir to quantify both the free-surface aeration and bubbly seepage motion, as well as the bubbly flow interactions at the step surfaces. Using a phase-detection probe in the free-surface flow and a high-speed camera in the gabion material, the experimental observations highlighted a complex air-water bubby flow motion. The interactions between seepage and free-surface flow were intense, leading to a modified cavity recirculation flow motion, compared to impervious stepped spillways. The quantitative measurements highlighted the strong aeration of the free-surface flow with void fractions ranging from non-zero values close to the gabion to unity above the free-surface. The cavity flow was in contrast drastically less aerated, but the bubbly flow measurements showed relatively large bubble velocities in the gabions, particularly next to the step edges. Large velocity fluctuations were also observed throughout the gabion materials. Altogether the findings demonstrated the turbulent aerated nature of the seepage flow and provided new insights into the complicated interactions between seepage and cavity recirculation motions.