Author(s): Rob Uittenbogaard; John Cornelisse; Scott Socolofsky; Yann Friocourt
Linked Author(s): Scott A. Socolofsky
Keywords: Bubble plume; Density stratification; Current; Salt intrusion; Energy efficiency
Abstract: This paper reports on a part of our research on the application of bubble plumes for reducing the intrusion of seawater in a 15m deep salt-stratified tidal channel (the Rotterdam Waterway in The Netherlands) .We set the relevant prototype conditions at 15m depth, 1. 5 m/s maximum current and 1 psu/m maximum salt-stratification. The prime objective of this part of our research is to determine the efficiency of converting (air-compressor) energy into increasing the potential energy of a salt-stratified current under prototype conditions, e. g. ,reducing the stratification by mixing. In stagnant density-stratified water, the vertical transport of water by bubble plumes has been explored, although mostly at small laboratory scales. Estimates for the energy efficiency of the bubble plume for upward transport and mixing of denser water in stagnant density-stratified water are presented in (Zic et al. ,1990; Lemckert& Imberger, 1992; Asaeda& Imberger, 1993; Socolofsky& Adams 2003) . For the first time we explored the essential properties of a bubble plume in a salt-stratified current by the equivalent case of a bubble plume towed through stagnant water salt-stratified at 10 psu/m. We ran laboratory experiments at 0. 7m water depth in a canal at Texas A& M and at 2. 5m water depth in Deltares’50m long water-soil tank; the bubble plume was towed up to 0. 4 m/s. From the change in density profile per tow run we derive the vertical salt-mass transport of the bubble plume as well as the efficiency of converting the energy provided by expanding bubbles into potential energy of density-stratified water. In addition, by using 4 different camera viewing directions, by dye injection in front of the plume at several different depth levels, as well as, by velocity recordings we observed the plume angle, the plume’s non-circular cross section when towed, and the flow pattern around the plume.
Year: 2015