Experiments and Modeling of Bubbly Surface Jets

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This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5). Carrica0853286This research project will evaluate the effect of the presence of bubbles on the turbulence structure, velocity distribution and ultimately the water entrainment caused by surface jets, as well as the resulting gas phase distribution. There is ample experimental evidence that a surface jet issued horizontally, parallel to a free surface containing bubbles entrains more surrounding water than that of a single-phase. Besides furthering basic knowledge on two-phase surface jets, the project is designed to test the hypothesis that the presence of bubbles will increase the water entrained by the surface jet, and to provide a complete data set to evaluate two-phase flow models dealing with two-phase surface jets. The experiments will replicate those of Walker et al. (1995), but will add a Venturi-type bubble injector with gas volume fractions ranging from 0 to 30%. Velocities and Reynolds stresses will be measured with hot film probes using conditional averaging techniques. Gas volume fraction, bubble velocity and size distribution will be measured with a multiple tip glass optical phase detection probe. From the averaged velocity measurements mass and momentum balance calculations will be performed to infer the degree of water entrainment. The simulations are intended to test the ability of the available two-phase flow models to capture the experimental observations, and to identify the areas that need modeling improvements. This work will be the first study of the effects of bubbles on surface jets. This project has been developed for a doctoral thesis and so is a focused confluence of research and education. If successful, the project will advance the basic knowledge of jet/free surface interaction and the effects of bubbles on turbulence characterization and water entrainment. This project will help understand and improve modeling of flows downstream of spillways, where the presence of highly ventilated surface jets causes most numerical models to grossly under predict entrainment and thus the flow pattern. Better modeling capabilities can devise mitigation measures to reduce the bubble entrainment and transport to high depths that ultimately causes large total dissolved gas concentrations and bubble fish disease, which is of great environmental concern. Bubbly surface jets also appear in many engineering applications, notably on transom stern ships and in waterjet powered ships, of importance to national security.