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Non intrusive density measurements in gravity currents interacting with an obstacle

Adduce Claudia, Maggi Maria Rita, De Falco Maria Chiara

Acta Geophysica

2022

Vol. 70, no 5

2499--2510

Gravity currents are flows produced by a density difference between two fluids. Non-intrusive density measurements, based on image analysis, are employed to measure the instantaneous width averaged density fields of lock-release gravity currents. The developed technique uses dye concentration as a tracer. For each pixel of the acquired images, a calibration procedure is applied to relate the concentration of dye, uniformly distributed in the experimental tank, and the greyscale. Two calibration techniques with nine-image and two-image calibration curves, respectively, are employed to evaluate the instantaneous density fields of a gravity current with and without a bottom obstacle. The two different calibration curves affect the measurement results, i.e. instantaneous density fields, front propagation, current area and mixing. The image analysis using a nine-image calibration curve is found to give better results compared to the technique with a two-image calibration curve. The analysis performed shows how the image analysis based on a nine-image calibration curve is a more suitable technique for the study of the gravity currents dynamics and the associated mixing, which are strongly affected by the presence of a bottom obstacle.

On the possibility of convective overturning in the Słupsk Furrow overflow of the Baltic Sea

Zhurbas V., Elken J., Paka V., Piechura J., Chubarenko I., Väli G., Golenko N., Shchuka S.

Oceanologia

2011

No. 53 (3)

771-791

Closely spaced CTD transects across the Słupsk Furrow displayed a "downward-bending" of salinity contours below the salinity interface on the southern flank due to a transverse circulation in the saline water overflow. Numerical simulation of a gravity current in an idealized channel with geometry, dimensions and initial density stratification all much the same as in the Słupsk Furrow was applied to verify whether the downward-bending could be transformed into an inverted density stratification. Some arguments in favour of the possibility of convective overturning due to the differential transverse advection beneath the gravity current, brought on by the numerical simulations, are discussed.