Laboratory Experiments on Convective Entrainment Using a Saline Water Tank
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Entrainment fluxes in a shear-free convective boundary layer have been measured with a saline water tank set-up. The experiments were targeted towards measuring the entrainment behaviour for medium to high Richardson numbers and use a two-layer design, i.e. two stacked non-stratified (neutral) layers with different densities. With laser induced fluorescence (LIF), the entrainment flux of a fluorescent dye is measured for bulk Richardson numbers in the range 30–260. It is proposed that a carefully chosen combination of top-down and bottom-up processes improves the accuracy of LIF-based entrainment observations. The observed entrainment fluxes are about an order of magnitude lower than reported for thermal water tanks: the derived buoyancy entrainment ratio, \(A\), is found to be \(A \approx 0.02\), which is to be compared with \(A\approx 0.25\) for a thermal convection tank (Deardorff et al., J Fluid Mech 100:41–64, 1980). An extensive discussion is devoted to the influence of the Reynolds and Prandtl numbers in laboratory experiments on entrainment.
KeywordsConvective boundary layer Entrainment Laboratory experiments
The authors thank Jos Verdoold, Thijs Heus, Esther Hagen, Jeroen Lebouille, Daniel Abrahams, Erwin de Beus and Rob Rodink for their efforts towards improving the set-up. One of us (MAJ) acknowledges research project CGL2006-12474 from the Spanish Government. Han van Dop, Peter Sullivan, Evgeni Fedorovich and Jeff Weil are gratefully acknowledged for contributing useful insights.
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