Effect of Bubble Transport on Turbulent Dissipation in Aerated Flow of an Expanded-Drop Stilling Basin

Abstract Friction and shear between the jet flow and the hydraulic jump in a sudden-expansion stilling basin enhance air entrainment. A population balance model was employed to simulate the transport characteristics of entrained bubbles and their influence on turbulent energy dissipation. The results indicate that near the basin floor, the number density of bubbles with d a ≤ 0.5 mm reaches 29.58 bubbles/cm ³ , significantly exceeding the value of 2.10 bubbles/cm ³ observed in conventional stilling basins. The drag-buoyancy ratio ( R ( d + G )/ b ), which characterizes the vertical transport of bubbles of different sizes, reveals that bubbles with d a = 0.5 mm exhibit a ratio of 9.30 (indicating accumulation near the floor), whereas those with d a ≥ 4.0 mm have ratios below 1.00 (promoting escape to the surface). Under the combined effects of roller re-entrainment in the hydraulic jump and jet-induced variations in bubble drag ratio, the vertical turbulent dissipation rate exhibits a distinct "dual-peak" profile. Notably, in the floor impingement zone, the turbulent dissipation rate reaches 23.21 J·kg ⁻ ¹ ·s ⁻ ¹ —seven times higher than the 2.90 J·kg ⁻ ¹ ·s ⁻ ¹ observed in conventional stilling basins. These findings demonstrate that bubble transport characteristics in aerated flows, particularly the clustering effect of micro-bubbles, constitute the fundamental mechanism for enhanced energy dissipation in expanded plunging pools.