What Waterfalls and Kitchen Sinks have in Common: A Comparison between Vertical and Horizontal Supported Jets

In plunging jets and at hydraulic jumps, large amounts of air bubbles are entrained at the impingement of the liquid jet and receiving body (BIN, 1993; ERVINE, 1998; CHANSON, 2009a). Air is entrapped and advected into a turbulent shear layer with strong interactions between the air bubble advection process and momentum shear flow (GOLDRING et al. 1980, SENE et al. 1994, CHANSON 2008, 2009b). New air‐water flow measurements were repeated with identical inflow conditions in a vertical supported jet and horizontal hydraulic jump. Experiments were carried out at relatively large‐scale facilities with identical inflow water depths and inflow velocities at Froude numbers between 6.5 and 13.5. Basic flow observations yielded substantial differences between the two setups. Investigations of the impingement perimeter showed remarkably larger maximum amplitudes of the impingement perimeter fluctuations in the hydraulic jump. The fluctuation frequencies of the impingement perimeter showed an increasing trend with decreasing inflow velocity in the plunging jet, whereas the fluctuation frequencies were constant in the hydraulic jump for all inflow velocities. Detailed air‐water flow measurements were carried out with intrusive phase‐detection probes. They showed similarities in terms of void fraction distributions, as in both cases they followed a Gaussian profile with a pseudo‐exponential decay in maximum air content. Air‐water interfacial velocity profiles showed self‐similar distributions, albeit there were substantial differences between horizontal hydraulic jump flow and vertical plunging jet shear layer. The transfer of momentum between impinging jet and receiving water body, as well as the buoyancy force, were affected by the flow geometry. The momentum transfer in the plunging jet seemed to be little affected by the advective diffusion process, whereas in the hydraulic jump, there seemed be some interplay between momentum transfer and air‐bubble diffusion. Bubble chord size data showed similar trends for both setups, with positively skewed distributions in both plunging jet and hydraulic jump. Their stream wise evolution was characterised by a shift towards smaller bubbles.