Experimental analysis of Froude number effect on air entrainment in the hydraulic jump

Abstract

A hydraulic jump is characterized by strong energy dissipation and mixing, large-scale turbulence, air entrainment, waves, and spray. Despite recent pertinent studies, the interaction between air bubbles diffusion and momentum transfer is not completely understood. The objective of this paper is to present experimental results from new measurements performed in a rectangular horizontal flume with partially developed inflow conditions. The vertical distributions of the void fraction and the air bubbles count rate were recorded for inflow Froude number Fr 1 in the range from 5.2 to 14.3. Rapid detrainment process was observed near the jump toe, whereas the structure of the air diffusion layer was clearly observed over longer distances. These new data were compared with previous data generally collected at lower Froude numbers. The comparison demonstrated that, at a fixed distance from the jump toe, the maximum void fraction C max increases with the increasing Fr 1 . The vertical locations of the maximum void fraction and bubble count rate were consistent with previous studies. Finally, an empirical correlation between the upper boundary of the air diffusion layer and the distance from the impingement point was derived.

An Experimental Study of Hydraulic Jump in a Gradually Expanding Rectangular Stilling Basin with Roughened Bed

“…Bubbly two-phase flow in a hydraulic jump using a flow visualization technigue were studied by Mossa and Tolve [12]. The air-water flow properties in a hydraulic jump were extensively studied Gualtieri and Chanson [13], Chanson and Gualtieri [14], Gualtieri and Chanson [15] and Gualtieri and Chanson [16].…”

Effect of Froude number on bubble clustering in a hydraulic jump

“…In plunging jet and hydraulic jumps, such large-scale vortices are generated in the developing shear layers. As the vortical, coherent structures are advected downstream, they grow up in size by vortex pairing and contribute to further clustering (Gualtieri and Chanson 2007a). (Table 1).…”

“…The vertical probe position was adjusted by 0.1 mm increments. The experiments yielded the void fraction C and the bubble count rate F over the depth at various distances from the jump toe on the channel centreline (Gualtieri and Chanson 2007a). The air concentration or void fraction C is the proportion of time during which the probe tip is in air, whereas the bubble count rate F ¼ number of bubbles impacting the probe tip per second.…”

Boundary between air entrainment and air transport downstream of a hydraulic jump in circular conduits

“…The air entry will depend on different variables, as the upstream Froude number of the jet (Kalinske & Robertson, 1943), jet velocity (Kenn & Zanker, 1967), the recirculating vortex (Goldring et al, 1980), the surface roughness of the jet (Ervine et al, 1980). Chanson (1995) , Chanson & Gualtieri (2008), and Gualtieri & Chanson (2007) noted that viscous and surface tension effects are important for air entrainment of hydraulic jumps. Pothof & Clemens (2010), Pothof & Clemens (2011) found that the air transport for various flow regimes depends on the water flow number, pipe slope, and surface tension.…”