Flow Visualization in Bubbly Two-Phase Hydraulic Jump

European Journal of Mechanics - B/Fluids

2007

In an open channel, a hydraulic jump is the rapid transition from super-to sub-critical flow associated with strong turbulence and air bubble entrainment in the mixing layer. New experiments were performed at relatively large Reynolds numbers using phase-detection probes. Some new signal analysis provided characteristic air-water time and length scales of the vortical structures advecting the air bubbles in the developing shear flow. An analysis of the longitudinal air-water flow structure suggested little bubble clustering in the mixing layer, although an interparticle arrival time analysis showed some preferential bubble clustering for small bubbles with chord times below 3 ms. Correlation analyses yielded longitudinal air-water time scales T xx V 1 /d 1 of about 0.8 in average. The transverse integral length scale Z/d 1 of the eddies advecting entrained bubbles was typically between 0.25 and 0.4, irrespective of the inflow conditions within the range of the investigations. Overall the findings highlighted the complicated nature of the air-water flow.

“…1. This advective diffusion air layer was documented experimentally in past and present studies [4,6,7]. An example is shown in Fig.…”

Section: Basic Air-water Flow Propertiesmentioning

confidence: 91%

Bubbly flow structure in hydraulic jump

European Journal of Mechanics - B/Fluids

2007

“…In Fig. 6 the experimental data are compared with those available in the literature [5,12]. The jump toe pulsations are believed to be caused by the growth, advection and pairing of large scale vortices in the developing shear layer of the jump [12,13].…”

Section: Basic Patterns Of Air-water Flow Properties In the Hydraulicmentioning

confidence: 99%

“…More recently, Chanson [4] studied the air-water properties in partially developed hydraulic jumps, showing a similarity with plunging-jet entrainment. Mossa and Tolve [5] recorded instantaneous properties of bubbly flow structures using an imaging technique. Chanson and Brattberg [6] documented vertical distributions of void fractions, bubble count-rates and air-water velocities in the hydraulic jump with inflow Froude numbers Fr 1 of 6.33 and 8.48.…”

Section: Forewordmentioning

confidence: 99%

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

Gualtieri

2007

Environ Fluid Mech

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.

“…Relatively Fewer studies investigated hydraulic jumps with lower Froude numbers (Murzyn et al 2005, Chachereau andChanson 2011). Other research works also used flow visualization techniques (Mossa andTolve 1998, Leandro et al 2012). All experimental investigations in breaking jumps showed some intense air entrainment, with singular air entrapment at the roller toe and interfacial aeration across the roller free-surface .…”

Section: Hydraulic Jumpsmentioning

confidence: 99%

Are breaking waves, bores, surges and jumps the same flow?

Lubin

2016

Environ Fluid Mech

The flow structure in the aerated region of the roller generated by breaking waves remains a great challenge to study, with large quantities of entrained air and turbulence interactions making it very difficult to investigate in details. A number of analogies were proposed between breaking waves in deep or shallow water, tidal bores and hydraulic jumps. Many numerical models used to simulate waves in the surf zone do not implicitly simulate the breaking process of the waves, but are required to parameterise the wave-breaking effects, thus relying on experimental data. Analogies are also assumed to quantify the roller dynamics and the energy dissipation. The scope of this paper is to review the different analogies proposed in the literature and to discuss current practices. A thorough survey is offered and a discussion is developed an aimed at improving the use of possible breaking proxies. The most recent data are revisited and scrutinised for the use of most advanced numerical models to educe the surf zone hydrodynamics. In particular, the roller dynamics and geometrical characteristics are discussed. An open discussion is proposed to explore the actual practices and propose perspectives based on the most appropriate analogy, namely the tidal bore.