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[1] Microstructure measurements of a triple-diffusive staircase with a stability ratio of 1.1 are presented. Data were recorded at Lake Banyoles, a small lake in Catalonia, Spain, with a warm, salty, and turbid underground inflow. Turbulent scales are well resolved in the two observed convective layers and allow determination of the dissipation rates of the turbulent kinetic energy, e, and of the turbulent temperature fluctuations, c, which are found to be 3.3 Â 10 À7 C 2 /s and 2.7 Â 10 À9 W/kg for one of the layers and 5.9 Â 10 À7 C 2 /s and 3.8 Â 10 À9 W/kg for the other. Thermal spectra for the convective layers look universal in viscous-diffusive and viscous-convective subranges. Characteristic vertical displacements within convective layers could also be obtained on the basis of Thorpe scales and were found to be 0.3 times the layer thickness. Vertical convective fluctuations were estimated and found to be of the order of 10 À4 m/s. When turbulent fluxes were determined within the convective layers on the basis of microstructure data and compared to those at the diffusive interfaces, they showed a stationary state with a mean thermal flux of 3.5 Â 10 À6 C m/s. A comparison of experimental heat fluxes to different models favors the scaling model of Grossman and Lohse (2000) for RayleighBénard convection and the double-diffusive convection model of Fernando (1979aFernando ( , 1979b for low stability. If the 4/3 power law is assumed, then the parameterization proposed by Taylor (1988) for diffusive interfaces at low values of the density ratio is also in accordance with our data.Citation: Sánchez, X., and E. Roget (2007), Microstructure measurements and heat flux calculations of a triple-diffusive process in a lake within the diffusive layer convection regime,

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The theoretical models of Batchelor and Kraichnan, which account for the smallest scales of a scalar field passively advected by a turbulent fluid (Prandtl . 1), have been validated using shear and temperature profiles measured with a microstructure profiler in a lake. The value of the rate of dissipation of turbulent kinetic energy « has been computed by fitting the shear spectra to the Panchev and Kesich theoretical model and the one-dimensional spectra of the temperature gradient, once « is known, to the Batchelor and Kraichnan models and from it determining the value of the turbulent parameter q. The goodness of the fit between the spectra corresponding to these models and the measured data shows a very clear dependence on the degree of isotropy, which is estimated by the Cox number. The Kraichnan model adjusts better to the measured data than the Batchelor model, and the values of the turbulent parameter that better fit the experimental data are q B 5 4.4 6 0.8 and q K 5 7.9 6 2.5 for Batchelor and Kraichnan, respectively, when Cox $ 50. Once the turbulent parameter is fixed, a comparison of the value of « determined from fitting the thermal gradient spectra to the value obtained after fitting the shear spectra shows that the Kraichnan model gives a very good estimate of the dissipation, which the Batchelor model underestimates.

The flow induced in a long cylinder by an axially discharging round turbulent jet was investigated experimentally with applications to crude oil storage in the U.S. strategic petroleum reserves (SPR). It was found that the flow does not reach a true steady state, but vacillates periodically. Digital video recordings and particle image velocimetry were used to map the flow structures and velocity/vorticity fields, from which the frequency of jet switching, jet stopping distance, mean flow, turbulence characteristics, and the influence of end-wall boundary conditions were inferred. The results were parameterized using the characteristic length D and velocity J 1/2 /D scales based on the jet kinematic momentum flux J and cylinder width D. The scaling laws so developed could be used to extrapolate laboratory observations to SPR flows.