Hydraulic jumps and breaking bores: modelling and analysis

Abstract

In open channel flows, the transition from a rapid to fluvial flow motion is called a hydraulic jump. A related flow motion is a compression wave in a channel, such as a tidal bore or surge. A key feature of hydraulic jumps and breaking bores is the rapid spatial and temporal deformations of the free surface of the roller region, in response to the interactions between entrained air bubbles and turbulent structures. The flow structure in the roller remains a great research challenge due to large quantities of entrained air, bubble–turbulence interactions and the coupling between turbulent properties and free-surface deformations. Breaking bores and hydraulic jumps with a marked roller present a number of similar features that are discussed herein. Recent results have shown that the roller is a highly unsteady turbulent region, with both the roller toe and free surface constantly fluctuating with time and space, although the roller shape is quasi-two-dimensional on average. Downstream of the roller toe, air bubbles and vorticity are diffused in the shear zone at different rates. The double diffusive convection process leads to a complex interplay between instantaneous free-surface deformations, velocity fluctuations and interfacial processes including breakup and coalescence.