Chapter 7 - Air entrainment in hydraulic jumps

Abstract

This chapter provides an overview of air entrainment in hydraulic jumps. In open channels, the hydraulic jump is defined as the transition form a rapid to fluvial flow. It is characterized by the development of large-scale turbulence, surface waves and spray, energy dissipation, and air entrainment. The large-scale turbulence region is usually called the “roller”. Several researchers have presented clear pictures of the recirculation mechanisms and of large-scale turbulent eddies in the roller. Air bubbles and air packets are entrained at the jump toe into a free shear layer, characterized by intensive turbulence production, predominantly in vortices with horizontal axes perpendicular to the flow direction. Engineering applications of hydraulic jumps include energy dissipation, air entraining device, and mixing device. The comparative presentation of air concentration distribution along hydraulic jumps shows a marked difference in air bubble diffusion among partially-developed inflow, fully-developed inflow conditions, and pre-entrainment flow conditions. The equation applies to both horizontal hydraulic jump and vertical supported jet suggesting that the gravity effects have little affects on the diffusion process. The chapter concludes that the air bubble diffusion in fully-developed hydraulic jumps and pre-entrained hydraulic jumps exhibits different features..